Lange Review Ultrasonography Examination, 4th Edition
Chapter 7. Obstetrical and Gynecologic Sonography and Transvaginal Sonography
Charles S. Odwin, Cynthia A. Silkowski, and Arthur C. Fleischer
PATIENT CARE PREPARATION AND TECHNIQUES
Before starting an ultrasound examination, a thorough review of the patient’s history is needed.
You should introduce yourself to the patient and explain the scanning techniques utilized for the procedure. Patients have the right to refuse the ultrasound. Menstrual history, abnormal vaginal bleeding, pain, and previous surgery should be obtained in the history.
The patient’s referral diagnosis and clinical symptoms should be kept in mind as the history is reviewed. Often, the history will give clues as to the current abnormality. It is important to review the patient’s reproductive history as well. Gravida (G) refers to the pregnancies. Primigravida is a first time pregnancy; multigravida is many pregnancies. Nulligravida is a patient that has never been pregnant. Parity (P) is the condition of a woman with respect to her having borne viable offspring. Typically, parity is displayed as a four-digit series. The first number being the term births, the second number being preterm births, the third number being abortions (spontaneous, elective, missed or ectopic pregnancy) as well as complications of pregnancy <20 weeks resulting in abortion, and the fourth number being the number of living children.1 The duration of a pregnancy can be calculated from the first day of the last normal menstrual period and is referred to as menstrual age. The average duration of a pregnancy is approximately 280 days, 40 weeks, 9 calendar months, or 10 lunar months.1 The expected date of delivery can be estimated by Nagele’s rule, which is based on a 28-day menstrual cycle:
• Identify the date when the last menstrual period began
• Add 7 days
• Subtract 3 months
• Add 1 year
In addition to the medical history, laboratory tests should also be reviewed. For gynecologic sonograms, all blood work should be reviewed. An elevated white blood cell count could help diagnose an infectious mass, for example. Other tests might include pap smears, biopsies, and ovarian cancer screening tests (CA 125). For the obstetric patient, there are many laboratory tests that may be available at different stages in the pregnancy. Blood type should always be noted, as well as any antibody titers. In early pregnancy, serum hCG (human chorionic gonadotropin) titers may suggest failed pregnancy, ectopic pregnancy, or a normal intrauterine pregnancy depending on the levels.
Both gestational sac growth and hCG production relate to trophoblastic function. Any discrepancy between the two can suggest an abnormality in development. Markedly increased hCG may suggest twins or molar pregnancies. In the second trimester, all pregnant women may elect to have maternal serum alpha-fetoprotein (MSAF3) triple screen test, or alphafetoprotein 3 (AFP3). The number three refers to the markers tested, including AFP. These are unconjugated estriol and hCG. Assessment of MSAFP3 values is also related to such maternal factors as age, weight, diabetic status, multiple gestation, and race. Screening markers are used to calculate a woman’s risk of having a child with Down syndrome or neural tube defects.
Proper documentation is pertinent to any medical examination. The images should be labeled with patient identification and the anatomy shown on the image. If any abnormalities are identified, the images should also be labeled according to location so that others reviewing the images can locate the abnormality. All exams should be documented in some form of hard copy, such as x-ray film, optic disc, thermal paper, hard drive, or DVD. In addition, a written report of the exam should be included with the hard copy. The picture archiving and communications systems (PACS) is a digital image storage device that is currently replacing the previously mentioned hard copy. The device enables images such as ultrasound, x-ray, computed tomography (CT), and magnetic resonance imaging (MRI) to be digitally stored and viewed on a screen without fading or distortion. The final report may contain varied information but should include any measurements, reason for exam, ultrasound findings, and the doctor’s impression. For billing and coding purposes, all reports must contain a diagnosis derived from the exam or referral diagnosis that supports the billing code.
Hand washing should be done before and after every sonographic procedure in order to reduce hospital-acquired infection. Based on American Institute of Ultrasound in Medicine (AIUM) guidelines, on completion of the exam, all transabdominal probes should have excess gel wiped off with a clean towel and cleaned with a disinfectant cleaner. Commercially available moist towelettes work well and are easy to use.
Transvaginal probes are reusable intracavity instruments. Therefore, precautionary measures should be addressed. The microorganisms that cause sexually transmitted disease, including the human immunodeficiency virus (HIV), are sometimes present in the vaginal secretions. Although these microorganisms are usually transmitted through sexual contact with an infected partner, they can be transmitted by contaminated reusable instruments. The current methods used to prevent transmission of infection with transvaginal transducers are as follows:
1. Chemical disinfectants
2. Disposable probe cover (condoms, latex gloves, and sheaths)
Both are required to prevent cross-infection from the transducer because although the probe is covered, a microscopic tear in the cover will expose the transducer to the vaginal membrane and the external cervical os. The transducer should be disinfected before it is returned to the manufacturer or technical support staff for maintenance or repair.
The first steps in preparing the transducer for an examination is disinfecting the probe from disease-causing organism bacteria, viruses, and fungi. Several methods of disinfecting agents are available; most are cold chemical disinfectants, which are glutaraldehyde based (e.g., Cidex, MetriCide, Wavicide). The piezoelectric crystal of the transducer is heat sensitive. Therefore, steam autoclaves should not be used because excessive heat could destroy the transducer. The transducer manufacturers normally recommend the type of chemical that is safe for their transducers, specifications, and the time limit for transducer chemical immersion.
Transvaginal transducers are composed of metals, plastic, crystal, and bonding materials, and all are not constructed in the same way. Thus, a disinfectant chemical may be safe for some transducers but destructive to others. Sonographers should not attempt to disinfect a transducer until they have carefully reviewed the manufacturer’s instruction manual and consulted with the technical support staff regarding any changes that may have occurred since the manual was published. To avoid chemical spills and reduce chemical vapors to health care workers, a commercially available immersion station can be used but must comply with Occupational Safety and Health Administration (OSHA) and Joint Commission on Accreditation of Healthcare Organizations (JCAHO) regulatory requirements.
In addition to disinfectant requirements, a probe cover is employed. The probe covers are specially designed sheaths for covering the transducers; they are available in different sizes to fit all types of transducers. These covers are made of a variety of materials such as latex, polyethylene, and polyurethane and are approved by the U.S. Food and Drug Administration (FDA). Probe covers are also available in sterile or nonsterile packs. Patient and health care workers with latex hypersensitivity should use alternative covers and gloves. The used probe covers and gloves should be treated as potentially infectious waste and disposed of accordingly.
INTRODUCTION TO TRANSVAGINAL SONOGRAPHY
Transvaginal sonography (TVS) involves the insertion of a specifically designed transducer into the vagina for imaging pelvic structures. Numerous names have been applied to this type of scanning such as endovaginal, endocavity, endosonography, and transvaginal. The terms transvaginal and endovaginal are both descriptive of the technical approach to scanning and are not specific for imaging of the vagina. In fact, only a small area of the vagina is imaged; the images are predominantly of the uterus and its adnexa.
The concept of using high-frequency transducers within the vaginal cavity to image the uterus and adnexa derived from the basic concept of ultrasound physics. Placing the transducer in close proximity to the pelvic organs or structures allows the use of higher frequencies, which in turn provide better resolution, both axial and lateral. The close proximity of the transducer also results in reduced attenuation and better focusing. As a result, transvaginal sonography allows for earlier and more definitive diagnosis than is possible with conventional transabdominal techniques.
Transvaginal sonography (TVS) has many clinical obstetrical and gynecologic applications because of its ability to delineate the uterus and its adnexa. These include:
• Evaluation of the endometrium in women with postmenopausal bleeding or dysfunctional uterine bleeding (DUB)
• Evaluation of pelvic masses
• Diagnosis of ectopic pregnancy and other complicated early pregnancy
• Evaluation of the cervix
• Monitoring the follicles of an infertile patient who is undergoing ovulation induction
• Guiding the placement of the needle during follicular inspiration or aspiration of fluid from the cul-de-sac
• Evaluation of the fallopian tube
• Evaluation of blood flow to the gestational sac and uterine artery with Doppler imaging
• Achieving additional diagnostic information in conjunction with transabdominal sonography
• Detecting the presence of placenta previa
• Evaluation of the fetal intracranial anatomy and prolapse of the umbilical cord during the second and third trimesters
CONTRAINDICATIONS TO TRANSVAGINAL SONOGRAPHY
• Patients who decline the procedure
• Infants and children
• Elderly patients with narrow introitus or atrophic vaginitis who experience pain or discomfort during probe insertion
• Unconscious patient (without informed consent)
• Mentally insane (without a health care proxy or an administrative consent)
ADVANTAGES OF TRANSVAGINAL SONOGRAPHY
• Higher resolution
• Earlier and more definitive diagnosis
• Does not require a full urinary bladder
• Faster medical management
• Additional information
• Eliminates the discomfort during bladder filling
DISADVANTAGES OF TRANSVAGINAL SONOGRAPHY
• Limited field of view
• Large masses may not be seen because they are beyond the focal zone of the transducer
• Unable to see both ovaries on the same image
• Documentation of uterine size may be difficult because of magnification in the near field
• The confined space of the vagina limits the mobility of the transducer; therefore, complete sequential images obtained with transabdominal sonography cannot be achieved with transvaginal sonography
• Only the presenting parts of the fetus and cervix can be seen in the second and third trimester pregnancy with the transvaginal approach
The patient should void before the examination begins, and the procedure should be explained to the patient. If a male examiner is to perform the examination, a female chaperone should be present during the entire examination. The staff in the room should be introduced to the patient. The chaperone should be a permanent staff member of the faculty who is familiar with the procedure. Volunteers and family members are not appropriate chaperones. The name of the chaperone and time of the procedure should be documented.
Transducers for transvaginal scanning have a specific size, shape, and frequency. Their diameter ranges from 12 to 16 mm; this smaller-than-usual diameter allows easy penetration within the vaginal lumen without patient discomfort. In addition, these transducers are twice as long when compared to transabdominal transducers.
Because the normal length of the vaginal lumen is approximately 7.5–9.5 cm, the transvaginal transducer must be longer so that part of it can be inserted and the other part can serve as a handle for the operator. The normal range of frequency used in transvaginal sonography is 5–10 MHz, with a sector field of view of 90°-115°. The larger the sector fields of view, the larger the portion of the organ or structure that can be visualized.
COLOR DOPPLER SONOGRAPHY (CDS)
Transvaginal color Doppler is a combination of B-mode image, pulse-wave Doppler, and a color-flow display (triplex imaging). The direction of blood flow is indicated by assigning color to the Doppler-shifted echoes that are superimposed on the gray-scale image.
The direction of flow toward and away from the transducer is presented in different colors on the image. For example, red represents flow toward the transducer, whereas blue represents flow away from the transducer, and a mixture of colors represents turbulent flow. Color Doppler has several advantages. First, because a network of blood vessels occasionally can mimic follicles, color Doppler allows rapid differentiation between vascular structures and follicles. It also allows precise placement of the sample volume for Doppler waveform analysis.
POSITION OF THE PATIENT AND THE EXAMINATION TABLE
During the transvaginal examination, the patient is placed in the lithotomy position for insertion of the transducer and for scanning. The probe can be inserted by the patient, the physician, or the sonographer. When the patient does the insertion, the transducer cable should be held so that the patient cannot accidentally drop the transducer.
The ideal table is a gynecologic examination table that allows numerous degrees of pelvic tilt positions and has stirrups for the patient’s heels. The table is placed in a slight Fowler’s position (also called the reversed Trendelenburg position) (Fig. 7–1). Elevation of the thighs allows the transducer to be moved freely from side to side (horizontal plane). The gynecologic examination table allows free upward and downward movement of the transducer (vertical plane), and the slight Fowler’s position of the table allows pooling of the small amount of peritoneal fluid normally found in the region of the cul-de-sac, which allows better delineation of pelvic structures. The Trendelenburg position should not be used because it drains away this fluid. If a gynecologic examination table is unavailable, a flat examination table can be prepared by placing a cushion or inverted bedpan under the patient’s pelvis.
FIGURE 7–1. Examination table in a slight Fowler’s position with a 20° elevation. The patient is in the lithotomy position.
The commonly used transducer maneuvers for transvaginal sonography are:
a) In and out Fig. 7–2 (A)
b) Rotation Fig. 7–2 (B)
c) Anterior and posterior angulations Fig. 7–2 (C)
d) Right adnexal angulation Fig. 7–3 (D)
e) Left adnexal angulation Fig. 7–3 (E)
These maneuvers are limited by the size of the vaginal lumen. Fig. 7–2(A) illustrates the in-and-out motion of the transducer used to achieve variation in the depth of the imaging from the cervix to fundus. Imaging from cervix is optimized by gradual withdrawing the probe with up angulations. Fig. 7–2(B) illustrates the rotating motion of the transducer for obtaining various degrees of semiaxial to semicoronal planes. Fig. 7–2(C) illustrates the angling motion of the transducer within the vaginal canal to obtain images of the anterior and posterior cul-de-sac. The side-to-side movements used are to obtain images of the adnexa (Fig. 7–3 D and E).
FIGURE 7–2. Scanning techniques: (A) in and out; (B) rotating motion; (C) angling motion. (Reproduced with permission from Philips Healthcare.)
FIGURE 7–3. (D) Transducer in the right lateral fornix. (E) Transducer in the left lateral fornix. (Reproduced with permission from Philips Healthcare.)
The recently developed technique for evaluation of the endometrium using saline infusion into the endometrial lumen during transvaginal sonography, termed sonohysterography is becoming more frequently used in the gynecologist’s office or sonographic suites for the evaluation of suspected endometrial or certain myometrial disorders.2 The technique provides a means to detect polypoid endometrial lesions, submucosal fibroids, adhesions, and uterine malformations that affect the lumen and can cause bleeding or infertility. Because the CPT code that is used for billing is listed as “sonohysterography,” this is the preferred term.
Sonohysterography plays an important role in evaluation of the patient with unexplained postmenopausal bleeding and in those patients in whom the endometrium is thickened or indistinct on transvaginal sonography. Polyps are enigmatic tumors apparently caused by resistance to progesterone-induced apoptosis or exposure to excess endogenous or exogenous estrogen. They typically are associated with intermenstrual bleeding, cramping, or infertility. Carcinomas may also be polypoid or arise within polyps.3 Sonohysterography affords clear detection of the polyp and its pedicle. This is in contrast to a thickened endometrium as a result of endometrial hyperplasia or carcinoma.
Intraluminal fluid collections are frequently seen on transvaginal sonography. Although they may be associated with endometrial cancer in some patients, they are more frequently associated with such benign conditions as cervical stenosis.3 Sonohysterography can be used advantageously to outline endometrial surfaces. This review provides an overview to the clinical utility of sonohysterography, its limitations, as well as a discussion of the circumstances in which it should be ordered.
With the more extensive use of transvaginal sonography and small flexible catheters, the possibility of improved delineation of the endometrial lumen with intraluminal fluid instillation became possible.3 The technique uses sterile saline as a negative (anechoic) contrast media to outline the endometrial lumen under continuous transvaginal sonographic visualization.4
Sonohysterography is primarily used for evaluation of endometrial polyps, assessing the presence and extent of submucosal fibroids, detection of uterine synechiae, and in selected cases of uterine malformations that involve the endometrial lumen. The reader is referred to several excellent descriptions of the spectrum of sonographic findings with this technique.3, 5
Before saline instillation, the standard procedure for transvaginal sonography is followed, including covering the probe with a condom and placement of the transvaginal probe within the vaginal fornix and midvagina to optimally delineate the endometrial interfaces in both the long and short axes. The images should be recorded on hard-copy film, PACS, or DVD for later review.
Sonohysterography involves placement of a catheter into the uterine lumen through the endocervical canal. Catheter choices that can be used include insemination catheter, pediatric Foley, pediatric feeding tube, a plastic sonohysterography catheter, or a specially designed flexible catheter with an introducer (Akrad Co, Cranford, NJ). The Akrad catheter is preferred, because it can be introduced easily through the introducer into the cervix without much pain or discomfort (Fig. 7–4). The balloon catheter is recommended when trying to evaluate the uterine lumen for patency. Once the cervix is cleansed with a cleansing solution and stabilized with a speculum, the catheter can be advanced into the lumen, and 3–10 mL of sterile saline is injected during sonographic visualization. The slow instillation of saline, allowing reflux out of the cervix, also diminishes the possibility of pain during installation. The endometrium is imaged in both long and short axes, with specific attention to its regularity and thickness (Figs. 7–5, 7–6, and 7–7). Because of the dynamic nature of the examination, DVD recording of the procedure is recommended with a few representative frozen images recorded for interpretation.
FIGURE 7–4. Tampa catheter consists of an introducer and flexible catheter.
FIGURE 7–5. Diagram showing catheter in place. The catheter is advanced over the introducer and the tip is best positioned in the fundal position of the endometrial lumen.
FIGURE 7–6. Diagram showing transducer sweep in long axis.
FIGURE 7–7. Diagram showing transducer sweep in short axis.
The procedure is best performed in the early follicular phase. This avoids confusing images arising from mildly irregular interdigitating secretory endometrium or clot that may be encountered in the late secretory portion of the cycle and also decreases the possibility of dislodging an unsuspected early pregnancy. Because most endometrial polyps are echogenic, they can best be seen against the relatively hypoechoic proliferative phase endometrium.5Conversely, submucosal fibroids may best be imaged in the secretory phase because they are typically hypoechoic, and their relation to the displaced endometrium may be best delineated during this phase of the cycle.
Contraindications to sonohysterography include hematometra, extensive pelvic inflammatory disease, or significant cervical stenosis. Doxycycline (100 mg p.o. bid), can be given a few days before sonohysterography if pelvic inflammatory disease (PID) is suspected. Rarely an atrophic or stenotic vagina from aging or previous radiation therapy can produce significant discomfort, even with placement of the vaginal speculum.
Typically, the patient does not experience significant discomfort if the catheter is properly placed in the fundus, and only small amounts of fluid are gently infused and allowed to reflux out of the cervix. Prophylactic antibiotics are usually not needed, but preprocedural, nonsteroidal anti-inflammatory drugs (NSAIDs) are helpful to minimize uterine cramping.
TYPICAL SONOGRAPHIC FINDINGS
The intraluminal surface of the normal endometrium is usually delineated in its entirety after the introduction of intraluminal fluid. On short axis, the normal areas of endometrial invagination in both tubal ostia can be seen. In general, the endometrium measures up to 3 mm in thickness per single layer and should have a relatively regular and homogenous texture. The secretory phase endometrium is mildly irregular and may contain “endometrial wrinkles” a few millimeters in height, representing focal thickening in the interdigitated endometrial surface. The endometrium is typically similar in thickness and texture, but focal irregularities can be observed in some patients (Figs. 7–8 and 7–9).
FIGURE 7–8. Focal endometrial hyperplasia. The transvaginal sonogram shows focal thickening (between cursors) in the corpus.
FIGURE 7–9. Focal endometrial hyperplasia. After saline is instilled, there is focal thickening of the endometrium, which was found to represent hyperplasia.
Endometrial polyps are typically echogenic and project into the endometrial lumen (Fig. 7–10). In the nondistended endometrium, they typically displace the median echo, which may represent refluxed cervical mucus, and are best seen just before ovulation. As they enlarge, they can distend the cavity and may be apparent without iatrogenic distention of the endometrial lumen. Some are outlined by trapped intraluminal fluid, mucus, or blood. The vascularity of the pedicle can be demonstrated in some cases with transvaginal color Doppler sonography.
FIGURE 7–10. Echogenic polyp in the endometrial lumen.
Submucosal fibroids are typically hypoechoic and displace the basalis layer of the endometrium. Amount of extension into the myometrial layers is important to distinguish superficial submucosal fibroids from those that extend into the lumen may be treated with wire loop resections from the lumen, whereas submucosal or intramural fibroids require a transperitoneal approach. If a submucosal fibroid has a thin stalk, it may be removed by wire loop or alligator forceps, whereas those that extend beyond the endometrial-myometrial interface will not be amenable to wire loop resection.
Synechiae typically occur as the sequelae of intrauterine instrumentation. They may be either echogenic or hypoechoic, depending on their fibrous content. The hypoechoic synechiae are best delineated in the background of the typically echogenic secretory phase endometrium.6
Certain uterine malformations that affect the lumen, such as bicornuate or septated uteri, may be evaluated using 3D ultrasound and color doppler sonography (CDS). The presence or absence of a fundal cleft is important in distinguishing bicornuate uteri from septated uteri.
Color Doppler sonography may be helpful to identify the vascular pedicle of a polyp, as well as the vascular rim of certain leiomyomata. Sonohysterography is helpful in determining whether a polyp has a wide or narrow pedicle because those with a thin pedicle are more easily removed with a forceps in the office than those with a thick pedicle.
Sonohysterography is also particularly helpful in determining whether certain intraluminal cystic areas are within a polyp or the myometrium. Punctate cystic spaces are frequently seen within polyps as a result of glandular obstruction. They may also be seen within the myometrium in women who are on tamoxifen or a selective estrogen receptor modulator (SERM), possibly a result of reactivation of dormant adenomyosis.2
Sonohysterography affords detailed delineation of the endometrial surface. Polyps, submucosal fibroids, and synechiae are readily delineated using this technique.
This study guide provides a description of the major applications of TVS in obstetrics and gynecology. The reader is referred to the references listed at the end of this chapter for further information.
GYNECOLOGY (NORMAL PELVIC ANATOMY)
The female pelvic reproductive organs are divided into the external and internal genitalia.
The external genitalia is called vulva. The vulva or pudendum is a term for external genital organs that are visible on the skin. The internal genital organs are located in the true pelvis and are only visible during medical imaging or surgery.
The uterus is situated medially in the pelvis and posteriorly to the urinary bladder and anteriorly to the rectum. The uterus can be divided into four different regions: (1) cervix, (2) isthmus, (3) corpus, and (4) fundus (Fig. 7–11). The uterus has three primary functions: (1) menstruation, (2) pregnancy, and (3) labor. The cervix is the inferior portion of the uterus and invaginates into the vagina. The isthmus is superior to the cervix and begins at the internal os of the cervix. The corpus or body of the uterus is larger than the cervix. The fundus is the uppermost portion of the uterus and is located superiorly to where the fallopian tubes arise from the uterus.
FIGURE 7–11. Diagram of the normal female internal reproductive organs.
The uterus is composed of three layers of tissue:
1. Peritoneum (uterine covering)
2. Myometrium (uterine muscle)
3. Endometrium (uterine cavity)
The outer layer, or peritoneum, is the serosal layer. The muscular portion of the uterus is called the myometrium. The inner layer, where the two walls of the uterus meet, is called the endometrium. This layer varies in thickness and echogenicity with the menstrual cycle, and is described later in the chapter. The peritoneum is serous membrane that forms the lining of the abdominal and pelvic cavity. A fold of peritoneum forms three potential spaces in the female pelvic region, which are important to pelvic sonography. The peritoneum that covers the anterior surface of the uterus and the upper aspect of the bladder forms a cul-de-sac called anterior cul-de-sac or vesicouterine pouch. The peritoneum also covers the posterior surface of the uterus and the anterior surface of the rectum called the posterior cul-de-sac or pouch of Douglas. This is the most dependent position of the potential space, thus allowing any blood or free-fluid collections to accumulate in this space. A small amount of fluid is sometimes identified in the pouch of Douglas due to follicular fluid secondary to ovulation. The third peritoneal space is anterior to the bladder and is termed the prevesical or retropubic space.1
The myometrium is homogeneous in echo texture except in cases of fibroids, which can cause multiple changes in the normal texture of the uterus. On occasion, a portion of the myometrium painlessly contracts causing a focal thickness lasting 20–30 minutes. This will spontaneously disappear with time. This finding is physiologic and should not be confused with a pathologic finding. Transvaginal sonography provides an objective means to evaluate the uterine cervical length and configuration. The normal cervix is between 2.0 and 2.5 cm in length and shows no funneling or dilatation of the endocervical canal. A thin echogenic stripe in the endocervical canal can be seen in most cases and is contiguous with the endometrial canal (Fig. 7–12). The endocervical canal opens into the vagina at the external os of the cervix. A single or multiple small cyst masses are sometimes seen in and around the cervical canal and represent nabothian cysts (mucinous retention cyst), which are caused by occlusion of the ducts of the cervical secreting glands (Fig. 7–13).
FIGURE 7–12. Transvaginal sonogram of the endometrium in long axis.
FIGURE 7–13. Retroverted uterus with a nabothian cyst.
The size of the uterus varies and is dependent on the patient’s age and gestational status. Before puberty and after menopause, the uterus is small in size. During reproductive years, an increase in gravida usually results in an increase in uterine size.1 A prepubertal uterus is 2–4 cm in length, with the corpus (or body of uterus) half the length of the cervix. In an adult nulliparous woman, the uterine length is 6–8 cm, width 3–5 cm, and anteroposterior dimension 2–4 cm. The corpus and cervix are equal in length. An adult multiparous uterus is 8–9 cm × 4–5 cm × 3–5 cm with the corpus twice the length of the cervix. In post-menopausal women, the uterus atrophics, regardless of the gravida status premenopausally. The uterine measurements of a postmenopausal woman are 6.5–3.5 cm in length, 2–3 cm in width, and 2 cm anteroposterior dimensions.3 Because of the magnification and the relatively small field of view provided by transvaginal sonography, measurements to indicate the size of the uterus are best obtained with transabdominal sonography. The uterus can vary slightly in position depending on the distention of the bladder. The following descriptions refer to uterine position with an empty bladder. Ninety percent of the time, the uterus tilts forward in an anteverted position, meaning the uterus forms a 90° angle with the posterior vaginal wall. The uterus, however, may be in any of the following positions:
• Anteverted: The uterus tilts forward with a 90° angle to the posterior vaginal wall.
• Anteflexed: The uterine corpus is flexed anteriorly on the cervix, forming a sharp angle at the cervix.
• Retroverted: The uterus tilts backward without a sharp angle between the corpus and cervix.
• Retroflexed: The uterine corpus is flexed posteriorly on the cervix, forming a sharp angle at the cervix.
• Medianus: Midline position.
• Dextroversion: Right lateral deviation.
• Levoversion: Left lateral deviation.
Blood Supply to the Uterus
The uterine and ovarian arteries are branches of the internal iliac (hypogastric) artery. The uterine artery travels superiorly from the cervix, running laterally to the uterus in the broad ligament. At the junction of the uterus and fallopian tubes, the uterine artery joins with the ovarian artery. The uterine artery gives rise to the arcuate arteries, which course within the outer myometrium (Fig. 7–14) identifying the arcuate venous plexus. Imaging of these vessels can be enhanced with color vaginal sonography. The arcuate arteries branch into the radial arteries, which supply the inner layers of the myometrium and endometrium. They then branch into the straight and spiral arteries, which supply the endometrium. The venous channels of the pelvis follow a course similar to the arteries.1
FIGURE 7–14. Transvaginal sonogram of the uterus in short axis. Small arrows points to the arcuate plexus.
Congenital Abnormalities of the Uterus
Congenital abnormalities of the uterus result from improper fusion of the mullerian or paramesonephric ducts. As the ducts fuse, the septum that separates them breaks down, resulting in a single uterine cavity. The lack of fusion results in different uterine malformation, as shown in Fig. 7–15. Because of the close development of the corpus and cervix of the uterus, a uterine malformation may also affect the cervix and play a part in its function during pregnancy. The uterus develops in synchronicity with the urinary system. When congenital uterine abnormalities are present, the kidneys should be evaluated sonographically.3 In the absent of a kidney or an ectopic kidney, the uterus should be scanned for malformations. The bicornuate uterus is well recognized sonographically by two endometrial echoes in the cavities, which are widely separated.
FIGURE 7–15. Diagram of common types of congenital uterine abnormalities.
The endometrial lining is the innermost layer of the uterus. It is greatly influenced by hormones and is responsible for accepting the embryo for implantation. Transvaginal sonography provides detailed delineation of the thickness and texture of the endometrium. The endometrium should be measured in its thickest anterior/posterior thickness as portrayed in its long axis (bilayer thickness).
Although the image and measurement are used to characterize the endometrium, they must be evaluated completely and characterized by scanning sweeps performed in the long and short axis of the uterus. In women of childbearing age, the endometrium measures between 3 and 6 mm in the proliferative phase (days 5–9 postmenstruation) and up to 14–16 mm in the secretory phase (days 14–28).
The texture changes from isoechoic to multilayered in mid-cycle to echogenic in the midsecretory phase. In postmenopausal women, the endometrial lining atrophics. Any uterine bleeding during this stage is considered abnormal.3 A common cause of vaginal bleeding in postmenopausal women is endometrial hyperplasia.5 In a postmenopausal woman, the endometrium should be 6 mm bilayer thickness and homogenous in texture. This is true for most women taking hormone replacement therapy. Punctate cysts can be seen in the inner myometrium in women taking tamoxifen. These are thought to represent reactivated adenomyomas. Polyps typically appear as echogenic endometrial masses that are insinuated between endometrial layers. They are especially seen when saline infusion SHG is performed.
Endometrial carcinoma typically causes asymmetry and irregularity of the endometrium. If there is invasion, the endometrialmyometrial junction is disrupted. Endometrial cancer is more commonly diagnosed in women 60–70 years of age but can occur at earlier ages. Symptoms may include metrorrhagia, menorrhagia, or both. Clinically, these symptoms are similar to endometrial hyperplasia and polyps. In woman not on hormone replacement therapy.2, 3the endometrial lining may be increased >5–6 mm on sonogram. An endometrial lining of > 5 mm is generally considered abnormal in postmenopausal patients on hormone replacement therapy.2, 3 The endometrial lining appears echogenic and may have irregular contours of the endometrium as the cancer invades into the myometrium. The diagnosis is made by endometrial biopsy.2, 3, 5
The ovaries are ellipsoid in shape, measuring approximately 3 cm in long axis and 2 cm in anteroposterior and transverse dimensions.5 The ovaries are located lateral to the uterus in the ovarian fossa (also known as the fossa of Waldeyer). The ovarian fossa is bound laterally by the internal iliac artery and vein. The medial boundary is the uterus.1 The normal ovaries are homogeneous in echo texture with the medulla appearing more echogenic. Multiple small follicular cysts may be seen peripherally in the cortex (Fig. 7–16). In most cases, transvaginal ultrasound gives a better visualization of the ovaries due to the close proximity of the transducer, which allows a higher frequency transducer to be used. This in turn provides better resolution. To image the right ovary using the transvaginal approach, the sonographer moves the transducer handle toward the patient’s left thigh so that the tip of the transducer probe is in the right lateral fornix. To image the left ovary, the sonographer moves the handle toward the patient’s right thigh so that the tip of the probe is in the left lateral fornix. Although the ovaries can be depicted from almost any parauterine position, they are usually depicted either lateral to the uterus or in the cul-de-sac. Unlike transabdominal sonography which allows the simultaneous imaging of both ovaries relatively often, transvaginal sonography can best image only one ovary at a time. Sonographically, the appearance of the ovaries varies with patient age, stage in menstrual cycle, pregnancy status, and body habitus. In reproductive years, the ovaries may be identified by follicles surrounding the outer edge of the ovaries. Follicular cysts are small (<3-5 mm), smooth, thin walled, and anechoic with good sound through transmission. Follicles will increase in size through the cycle with multiple follicles visible at days 5–7. At days 8–12, one or more dominant follicles (>10 mm) will begin to emerge. The dominant follicle reaches a mean diameter of 20 mm with a hypoechoic rim. After the ovum is released, bleeding may occur in the follicle, causing it to appear echogenic. The follicular cyst becomes a corpus luteal cyst with thick walls and appears anechoic to hypoechoic. The corpus luteal cyst will retain fluid for 4–5 days and measures approximately 2–3 cm. The corpus luteal cyst has a rich blood supply. Color-flow Doppler will reveal a ring of color around the periphery of the cyst. If no pregnancy occurs, the corpus luteal cyst will gradually atrophy. If pregnancy occurs, the corpus luteal cyst will remain and gradually regress by 12–14 weeks.2 The follicular cyst and corpus luteal cysts are all functional cysts of the ovary.1 In postmenopausal women, it is more difficult to identify the ovaries because of the absence of follicles and atrophy of the ovaries.3, 5 In patients who have had a hysterectomy, the ovaries can be difficult to depict because of the air-filled bowel occupying the space left by the removal of the uterus.
FIGURE 7–16. Transvaginal sagittal sonogram of the left ovary with normal follicles. The internal iliac vein and artery is seen posterior to the ovary.
The fallopian tubes originate at the lateral aspect of the uterus, known as the cornua. Fallopian tubes vary in length from 7 to 12 cm. Each Fallopian tube is divided into five subdivisions: (1) interstitial, (2) isthmus, (3) ampulla, (4) infundibulum, and (5) fimbriae.1 The interstitial portion of the tube sonographically appears as a fine echogenic line extending from the endometrial canal and traveling through the myometrium to cornua of the uterus.7 The isthmus is the narrowest portion of the tube and is located adjacent to the interstitial segment at the uterine cornua. The tube continues laterally and widens to form the ampulla. The infundibulum is the most lateral portion of the tube and opens to the peritoneum at the fimbria.1 The purpose of the fallopian tube is to aid in fertilization and to transport the ova from the ovary to the uterus. The normal fallopian tubes are difficult to identify by transabdominal or transvaginal sonography unless they are surrounded by fluid or filled with fluid.5
The uterus is loosely suspended in the center of the pelvic cavity by
• Round ligaments
• Uterosacral ligaments
• Cardinal ligaments
Although the uterus is suspended by ligaments, it has freedom of movement. During pregnancy, or in the presence of a uterine mass, the uterus moves upward, and during uterine prolapse, it moves downward. The upper portion of the uterus is supported by a series of ligaments. The cardinal ligaments or transverse cervical ligaments originate from the cervix and uterine corpus and insert on a broad portion of the lateral pelvic wall and sacrum. At the distal portion, this ligament is called the uterosacral ligament. This ligament anchors the cervix and is responsible for the uterine orientation.1
The two round ligaments originate from the uterine cornua and are located in a fold of the peritoneum and terminate in the upper portion of the labia majora.1 This ligament is responsible for the anterior tilt of the uterus and aids in stabilizing the fundus of the uterus.
There are two ligaments that are not true ligaments, but are folds of the peritoneum. The first is the suspensory ligament. It arises from the pelvic sidewall and contains ovarian vessels. It aids in supporting both the fallopian tube and ovary within the broad ligament.2 The broad ligament is also a double fold of the peritoneum. It fans over the adnexa and divides the anterior and posterior portions of the pelvis.1 It does very little to actually support the uterus. The broad ligament is not usually seen on ultrasound except in cases of pelvic ascites or ruptured cyst or hemoperitoneum.8
A series of different muscle bundles pass through the female pelvis. Some of these muscles are easily visualized by sonography and can often be confused for adnexal structures. The most commonly visualized muscle is the iliopsoas muscle. On sagittal views, it appears as a paired long hypoechoic stripe with echogenic linear lines. On transverse images, however, it appears ovoid and is visualized lateral and anterior to the iliac crests.1 The iliopsoas muscle descends until it attaches on the lesser trochanter of the femur. This can often be confused for an ovary until the sagittal view is obtained. The pelvic muscles can be identified sonographically by their appearance. The muscles appear hypoechoic and exhibit linear internal echoes. The borders of the muscles are echogenic representing the fascia.3, 5 The rectus abdominis muscle is located in the anterior abdominal wall and extends from the xiphoid process to the symphysis pubis. The obturator internus muscles are bilateral muscles lining the lateral margin of the true pelvis; they lie lateral to the ovaries. The levator ani muscle is a hammock-like muscle that extends from the body of the pubis and ischial spine to the coccyx.
Bladder and Ureters
The urinary bladder is a thick-walled distendable muscle that lies anterior to the uterus. It is fixed in position inferiorly at the symphysis pubis. This lower region is described as the trigone, defined by the orifices of the two ureters and a urethra. The bladder is thicker and more rigid here than at any other location.1 The ureter originates at the renal pelvis and descends anterior to the internal iliac artery and posterior to the ovary. The ureter travels from posterior to anterior and closely follows the uterine artery in its inferior portion. It then passes anteromedially to enter the trigone of the bladder.1 During a transabdominal sonographic examination of the pelvis, the urinary bladder must be distended for a variety of reasons. This is because (1) the urine-filled bladder pushes the bowel cephalad out of the true pelvic cavity; (2) it pushes the uterus cephalad away from the symphysis pubis; (3) it permits rapid anatomic orientation; (4) it provides a low-attenuation pathway to which ultrasound can propagate; and (5) it helps to elevate the head of the fetus for easy measurements. Whereas a distended bladder is an extremely important prerequisite for a transabdominal study, an empty bladder is the most important prerequisite for a transvaginal study. The failure to fill the bladder adequately for transabdominal studies can result in serious diagnostic errors. On the other hand, an overdistended bladder can also result in errors. Sonographically, the position and shape of the uterus have an effect on the urinary bladder. If the uterus is anteverted, the normally distended bladder has a mild indentation on its posterocephalad region. If the uterus is surgically removed or absent, the bladder has a different contour. Therefore, bladder contour depends on the shape and position of its surrounding structures. When the bladder is being filled, urine can be observed entering the bladder on real-time and has been referred to as the “ureteral jets.”2 The jets begin at the ureteral orifices and flow toward the center of the bladder (Fig 7–17). Bladder diverticula may be acquired or congenital. Acquired diverticula result more commonly from bladder outlet obstruction. Congenital diverticula are located near the ureteral orifice and are known as Hutch diverticula.3, 5 Sonographically, bladder diverticula appear as outpouching sacs from the bladder wall with an opening in one end of the sac that communicates with the bladder.
FIGURE 7–17. Transverse sonogram of the urinary bladder with color Doppler demonstrating ureteral jet.
The most common uterine tumors are fibroids (also known as leiomyoma, myoma, and fibromyoma). They are present in 25% of the female population and occur at approximately 30–35 years of age, with a higher percentage in the African-American population and becoming more prevalent with advancing female age. Fibroids are thought to be estrogen stimulated, so they tend to increase in size during pregnancy and decrease in size after menopause. Fibroids are classified according to their location on the uterus (Fig. 7–18). If the fibroid is confined in the myometrium, it is called intramural. If is located in the uterine cavity, it is called submucosal, and if projecting from the peritoneal surface, it is called subserosal. Often, they are found on pelvic examination without the patient having symptoms. When symptoms do occur, they can include abnormal bleeding, abdominal pressure, increased urinary frequency, and increased abdominal girth. The malignant form of the leiomyoma, a leiomyosarcoma, though rare, is believed to arise from a preexisting fibroid.1 Leiomyosarcoma accounts for about 1.3% of uterine malignancies.3 On sonogram, it appears similar to the leiomyoma and can be extremely difficult to diagnose preoperatively. Rapid accelerated growth may be the only clinical indication of a possible malignant process.3, 5 Fibroids has variable sonographic appearance:
FIGURE 7–18. Diagram demonstrating various locations of fibroids.
• Inhomogeneous uterine texture
• Enlarged, irregular-shaped uterus
• Calcifications with distal acoustic shadowing
• Solid mass on the uterus that cannot be separated from the uterus
• Displacement of the endometrium
• Diffuse uterine enlargement
Fig. 7–19A shows an enlarged uterus with inhomogeneous echotexture. Fig. 7–19B demonstrates an intramural fibroid in the fundus of the uterus. Fig. 7–19C shows gross pathologic findings of the uterus with multiple fibroids.
FIGURE 7–19A. Transabdominal sagittal sonogram of an enlarged uterus with fundal myoma.
FIGURE 7–19B. Transabdominal sagittal sonogram of a fundal myoma.
FIGURE 7–19C. Gross pathologic findings of the uterus with fibroids.
Degeneration and necrosis of fibrous tissue can produce cystic spaces within the fibroids. Fibroids are the most common cause of uterine enlargement in the nonpregnant female. When the uterus is enlarged >14 cm in length, the kidneys should be scanned for hydronephrosis. A large fibroid uterus may compress the ureter as it enters the pelvis, resulting in obstruction in flow of urine. Fibroids in the uterine cavity can on some occasions cause heavy vaginal bleeding resulting in acute anemia.
Adenomyosis is defined as an invasion of endometrial tissue into the myometrium >2 mm. It occurs more often in multiparous women. Symptoms may include menorrhagia, dysmenorrhea, and pelvic tenderness.9Sonographically; the uterus is large with small cysts visible in the inner myometrium. Often the myometrium of the uterus will appear inhomogeneous, similar to a fibroid, but distinct borders cannot be identified.3, 5
Hematocolpos is an accumulation of blood within the vagina. This condition can be caused by an imperforate hymen or transverse vaginal septum.3 On ultrasound, the vaginal cavity is distended with hypoechoic echoes and possible fluid/fluid levels, representing retained blood. Because the vagina can be distended to the same size of the uterine fundus, it may have an hourglass appearance.
Hematometra is an accumulation of blood within the uterine cavity secondary to atrophy of the endocervical canal or cervical stenosis. Sonographically, hematometra appears as marked distention of the uterus. Table 7–1 defines the terminology used to describe abnormal vaginal bleeding.
TABLE 7–1 Abnormal Bleeding Terminology
Menorrhagia-prolonged bleeding occurring at the time of a menstrual period, either in duration or volume
Metrorrhagia-uterine bleeding occurring at irregular intervals
Metromenorrhagia-excessive and prolonged bleeding occurring at irregular, frequent intervals
Benign cystic masses of the ovaries tend to be smooth walled, well-defined, and anechoic with increased posterior acoustic enhancement (Fig. 7–20). The normal ovaries in reproductive-age women have multiple follicles of various sizes (mature and immature). These follicles serve as anatomic sonographic markers to identify the ovaries. A follicular cyst occurs when a mature follicle fails to ovulate. The size of these follicles depends on the menstrual cycle.3The mature follicle measures approximately 20–25 mm.3 A follicular cyst is a functional cyst. The three most common functional cysts of the ovaries are (1) follicular cysts, (2) corpus luteal cysts, and (3) thecaluteal cysts.1, 3, 5Sonographers should be aware of the normal cyclic changes of the ovaries and their normal multiple sonographic appearances. Fig. 7–21 shows normal ovaries with a follicular cyst.
FIGURE 7–20. Right ovarian cyst.
FIGURE 7–21. Left ovary with follicles.
Transvaginal sonography is an accurate means of evaluating the ovaries and adnexal structures for the presence or absence of a pelvic mass. Pelvic masses can be characterized according to their location (organ of origin) and internal consistency (cystic, solid, mixed, septated, multiloculated). Such physiologic cysts as the corpus luteum cyst can be characterized as arising from within or around the ovary, whereas such extra ovarian masses as endometriomas appear outside the ovary.
Cystic masses must be scrutinized with transvaginal sonography for the intactness of their walls and the presence of any papillary excrescence. Internal structures such as septate or solid areas need to be shown in a minimum of two imaging planes.
Polycystic ovarian disease is an endocrinologic disorder characterized by excessive ovarian androgen production, which has spectrums of clinical manifestations10:
• Type 2 diabetes
Polycystic ovaries are sonographically characterized by bilateral enlarged ovaries with an increased number of small immature follicles ranging in size from 3 to 5 mm and there are usually more than eight on each ovary (Fig. 7–22).
FIGURE 7–22. Polycystic ovary.
Ovarian torsion refers to the twisting of the ovary and its vessels resulting in occlusion of its blood supply. The twisting of the ovary with the vascular pedicle on its axis results in arterial, venous, and lymphatic obstruction causing necrosis of the ovary.3, 5 Approximately 95% of cases are associated with an adnexal mass. The right adnexa are more commonly involved due to the sigmoid colon occupying the left lower quadrant.3, 5, 10 The most common mass associated with ovarian torsion is the dermoid cyst. The sonographic appearance of ovarian torsion will depend on whether the torsion is partial, intermittent, or complete. This type of mass is sonographically characterized by hyperechogenic areas, fluid/fluid layering, and calcifications within the mass. Color Doppler sonography is important in the evaluation of suspected torsion (Table 7–2).
TABLE 7–2 • Doppler Findings for Ovarian Torsion
Fig. 7–23A shows a left ovary and ovarian mass. Fig. 7–23B shows color and spectral Doppler with no flow. Fig. 7–23C shows gross pathologic findings of a necrotic ovary and ovarian mass surgically removed after an ovarian torsion.
FIGURE 7–23A. enlarged left ovary with an ovarian mass.
FIGURE 7–23B. Spectral and color Doppler with absence of flow.
FIGURE 7–23C. Gross pathologic ovarian torsion.
Malignant ovarian disease has a peak incidence between the ages of 55 and 59 years. Other risk factors include family history (maternal or sibling), number of years of ovulation, and environmental (Tables 7–3, 7–4, 7–5).2
TABLE 7–3 • Ovarian Cystic Masses
TABLE 7–4 • Ovarian Solid Tumors
TABLE 7–5 • Complex Ovarian Tumors
Human Chorionic Gonadotropin (hCG). hCG is a glycoprotein secreted by the syncytiotrophoblastic cells of the trophoblast.1, 11 The hCG is composed of two dissimilar subunits, alpha and beta. The antibodies against the beta subunit are used specifically to measure hCG.1 The quantitative beta hCG is very helpful in the diagnosis of ectopic pregnancy, gestational trophoblastic disease, or abnormal pregnancy.
During the first trimester of pregnancy, the serum beta hCG normally doubles every 48 hours (2 days) or increases at least 66% every 48 hours before 8 weeks of gestation. In the presence of ectopic pregnancy, approximately 80% of serum beta hCG has abnormal doubling beta (low doubling time, remain the same, or decrease slightly). However, 10% of ectopic pregnancies may have a normal doubling in 48 hours but may eventually drop in titers or plateau.11 A constant decreasing serial quantitative serum beta hCG in the first trimester is indicative of an abnormal pregnancy, regardless of the pregnancy location.
The serum levels for twins are twice as high as those for singleton pregnancies, and patients with a benign mole have higher levels than women with a normal pregnancy. Those with an invasive mole have higher ratios than those with noninvasive moles, and those with choriocarcinoma have even higher levels than those with invasive moles.3
There are various methods of reporting beta hCG. Some laboratories report serum quantitative beta hCG results in terms of International Reference Preparation (1st IRP), whereas others report the results in terms of Second International Standard (2nd IS). The most current is the Third International Standard (3rd IS). The 3rd IS is identical to the 1st IRP and 1.8 times those reported for the 2nd IS. Therefore, values in terms of the 3rd IS have been calculated by multiplying the 2nd IS by 1.88, which is the conversion factor.11, 12
Rapid Qualitative Pregnancy Test. This small kit used for detection of hCG in urine or serum is readily available for immediate hospital or office use and is now available over the counter for private use. Beta hCG is a hormone that is normally produced by the placenta and present in the serum and urine of a pregnant woman. This rapid kit is an excellent marker on qualitative confirmation of pregnancy while awaiting the result of the more accurate quantitative serum beta hCG. The kit uses a color-coded result in a small result window, as the sample contains a detectable amount of hCG in 3–5 minutes. A minus (-) result in the result window means not pregnant or below the range of hCG sensitivity. A plus (+) in the result window indicates pregnancy or was recently pregnant. The first morning urine usually has a higher level of hCG present.
The sensitivity for urine varies from 20 to 25 mIU/mL as early as 7–10 days postconception with an accuracy of 99%. A false-negative result can occur with a urine sample that is too diluted. Therefore, to avoid a false-negative result, the test should be performed before high volume of fluid ingestion for sonography or high volume of intravenous fluid hydration. The test can also be false-negative if the sensitivity of the detectable hCG levels is below 20 mIU/mL. Fertility drugs containing hCG, such as Pergonal can alter the result.1, 10
Serum Beta hCG Correlation with Ultrasound
The level of serum beta hCG to which a gestational sac should be seen on ultrasound is called the discriminatory zone. This concept was developed by Kadar et al., who correlated the ultrasound findings from patients with intrauterine pregnancy with serum beta hCG values using transabdominal scanning. This zone was between 6,000 and 6,500 mIU/mL of hCG using the First International Reference Preparation (1st IRP).11, 12 Later, Nyberg et al. reported a modification of the discriminatory zone at 1,800 mIU/mL Second International Standard (2nd IS), which is equivalent to 3,600 mIU/mL 1st IRP11
The 2nd IS was released by the World Health Organization (WHO), which is approximately one-half of IRP values.11 The most current beta hCG levels to which an intrauterine gestational sac can be seen with transvaginal ultrasound is now about 1,000–1,500 mIU/mL, depending on the frequency of the transvaginal probe used.3 The increased sensitivity in the detectable amount of hCG in the urine and serum of pregnant women and the rapid advancement in computers, real-time ultrasound equipment are constantly changing. Therefore, the current level to which a gestational sac should be seen on ultrasound is expected to decrease as the technology advances. If the gestational sac is not seen at this level, the pregnancy may be either abnormal or ectopic. However, a repeated level may be needed to confirm. On some rare occasions, the serum beta hCG may be positive without evidence of pregnancy or disease; this is known as phantom beta hCG or false-positive hCG test. Antibodies generated in the body against other human antibodies may bind both human and animal antibodies (heterophilic antibodies). These may interfere with hCG tests, by causing phantom hCG or false-positive hCG results. Surgery and chemotherapy are sometimes performed for ectopic pregnancy, solely on the basis of phantom or false-positive hCG test data.13 The interfering antibodies are present in serum but not urine samples. Phantom hCG can be confirmed by the demonstration of loss of the hCG in the urine samples.13
The Progesterone Level
Progesterone levels normally increase with gestational age. However, when an ectopic pregnancy is present, the corpus luteum does not secrete as much progesterone as occurs in normal pregnancy. Therefore, the concentration of the serum progesterone is usually lower in ectopic pregnancies. A value of 25 ng/mL or more is, 98% of the time, associated with a normal intrauterine pregnancy, whereas a value <5 ng/mL identifies a nonviable pregnancy, regardless of its location.10
The combination of serum beta hCG, progesterone level, and transvaginal sonography has resulted in great improvement in the diagnosis and management of ectopic pregnancy over the last 15–20 years.
Any pregnancy outside the endometrial cavity is called ectopic pregnancy (Fig. 7–24). The incidence of this type of pregnancy has increased, but the rate of death from ectopic pregnancy has declined. This decrease is the result of earlier diagnosis.3 Most ectopic pregnancies occur in the fallopian tube, approximately 90%. They account for approximately 12% of all maternal deaths.1 They can occur in any anatomic segments of the fallopian tube but occur more frequently in the ampullary region. Other, less common sites for ectopic implantation are the uterine cervix, ovaries, and abdomen. If the pregnancy is in the abdomen with advanced gestational age, transabdominal scans should be performed first, and if necessary, transvaginal scans should be performed. Abdominal pregnancy is the only form of ectopic pregnancy that can go to term. The incidence of live-birth after an abdominal pregnancy is very rare. I have only seen two of these cases go to term in my 28 years of experience, and both were delivered by abdominal surgery. In both cases, the placenta was left in the abdomen after surgery. On occasion, the placenta in an abdominal pregnancy may be adherent to bowel and blood vessels; removal could result in massive hemorrhage. In such cases, the placenta is left in situ and ultimately resorbs.1, 10
FIGURE 7–24. Diagram demonstrating various location of ectopic pregnancy.
Pseudogestational sac is blood or decidual cast in the uterine cavity mimicking a gestational sac. The differentiation between the gestational sac at 5–6 weeks and the pseudogestational sac are as follows:
A coexistent intrauterine pregnancy and ectopic pregnancy, known as heterotopic, can occur. It was first reported at a rate of 1 in 30,000, then 1 in 16,000, and most currently 1 in 39,000.1 This increase in heterotopic pregnancies may be attributable to increased ovulation induction.3,10 Twin ectopic pregnancy in the same Fallopian tube can also occur (Fig. 7–25). On rare occasions, an ectopic pregnancy can also occur in a previous cesarean section scar (Fig. 7–26). This patient had multiple previous cesarean sections and presented with vaginal bleeding in pregnancy. Cornual ectopic pregnancies are often misdiagnosed clinically and sonographically for multiple reasons. Its location allows clinical symptoms and rupture to occur late, approximately 12–16 weeks, and sonographically it can be misinterpreted as an intrauterine pregnancy with an eccentric implantation. Cornual ectopic pregnancy has a higher mortality when compared to other forms of ectopic pregnancies due to larger blood vessels at the implantation site and late rupture. Fig. 7–27 demonstrates a right cornual ectopic pregnancy.
FIGURE 7–25. Transvaginal sonogram with twin ectopic pregnancy in the same fallopian tube.
FIGURE 7–26. Transvaginal sagittal sonogram with an ectopic pregnancy in the cesarean section scar.
FIGURE 7–27. Transabdominal transverse scan with right cornual ectopic pregnancy.
Risk Factors for Ectopic Pregnancy
• Salpingitis from chlamydial infection or pelvic inflammatory disease
• Previous ectopic pregnancy
• Previous operations on the fallopian tube, bilateral tubal ligation, or tuboplasty surgery
• Cigarette smoking affects the ciliary action in the nasopharynx, respiratory tract, and fallopian tubes10
Clinical Signs and Symptoms of Unruptured Ectopic Pregnancy
• Unilateral pelvic pain, which increases in severity with time
• Vaginal spotting or bleeding
• Adnexal mass
• Positive pregnancy test
• Nausea and vomiting
Clinical Signs and Symptoms of Ruptured Ectopic Pregnancy
• Generalized abdominal pain
• Rebound tenderness
• Cervical motion tenderness
• Bilateral adnexal tenderness
• Right shoulder pain
• Tachycardia and hypotension
• Decreased hematocrit
UNRUPTURED ECTOPIC PREGNANCY
Ectopic pregnancy should be suspected when there is no intrauterine gestational sac and the serum beta hCG is at a level in which a pregnancy should be seen (values 1,500 mIU/mL or greater). The sonographic appearance of ectopic pregnancy primarily depends on whether the pregnancy is ruptured, unruptured, its location, and size. The sonographic equipment, the frequency of the transvaginal transducer, as well as the skills of the operator play important roles. Advanced ultrasound equipment in the hands of a skilled operator can sometimes depict an ectopic pregnancy before the patient begins to have clinical symptoms. Early depiction of ectopic pregnancy before a tubal rupture occurs is imperative to avoid the potential risk of massive blood loss and tubal damage. However, some patients delay seeking medical treatment when the symptoms start, arriving at the emergency department after rupture.
The sonographic appearance of an unruptured ectopic pregnancy is an adnexal ring-like mass with increased color flow around its periphery (“ring of fire”). The center of this adnexal ring is anechoic, and its periphery echogenic, resembling a doughnut. It is imperative for the sonographer to identify and depict the ovary on the side of the adnexal ring. A hemorrhagic corpus luteum cyst could mimic this finding. Rarely, an extrauterine gestational sac is seen with a live embryo. Fig. 7–28 depicts a live ectopic pregnancy in the posterior cul-de-sac.
FIGURE 7–28. Transabdominal sagittal scan with ectopic pregnancy in the posterior cul-de-sac.
Fig. 7–29A is a sagittal view demonstrating the uterine cavity free of any intrauterine pregnancy. Fig. 7–29B is of the same patient in a transverse view with an extrauterine gestational sac with an embryo.
FIGURE 7–29. (A) Transvaginal sagittal scan of the uterus, free of any intrauterine pregnancy. (B) Transvaginal coronal scan with a right unruptured ectopic pregnancy.
RUPTURED ECTOPIC PREGNANCY
An ectopic pregnancy in the fallopian tube grows linearly and circumferentially.10 The growth occurs more parallel than circumferentially due to more space and less resistance to growth in the long axis of the tube. This gives the ectopic pregnancy a sausage-shape appearance (Fig. 7–30). Rupture of the fallopian tube is due to maximum stretching of the tube with ischemia and necroses.
FIGURE 7–30. Diagram of a dilated fallopian tube due to an ectopic pregnancy.
After an ectopic pregnancy ruptures, blood accumulates in the abdomen and pelvis. It can readily be depicted with both transabdominal and transvaginal sonography. The blood may appear completely anechoic with some areas of echogenic fluid attributable to clotted blood. The patient is scanned in the supine position, allowing the free fluid to accumulate in a gravity-dependent position. The regions of Morison’s pouch, paracolic gutters, and posterior cul-de-sac are the most common locations for intraperitoneal blood after rupture. A ruptured hemorrhagic corpus luteum cyst could mimic a ruptured ectopic pregnancy both clinically and sonographically. The only type of ectopic pregnancy that is known to rupture without intraperitoneal collection is a cervical ectopic pregnancy. Patients with a large amount of blood in the abdomen may develop right shoulder pain because of diaphragmatic irritation, tachycardia, and hypotension secondary to vascular shock. There is no need to distend the urinary bladder in these cases because the intraperitoneal fluid is a good acoustic medium to view the abdominal and pelvic viscera. The ingestion of fluid to distend the urinary bladder for transabdominal scanning in a patient who is hemodynamically unstable may further delay immediate medical and surgical management and may further interfere with patients who need to be NPO for surgery. Sonographers should have experience in recognizing this emergency and call for assistance immediately. Fig. 7–31A shows free-fluid regions of Morison’s pouches. Fig. 7–31B shows the uterus free of any pregnancy. Fig. 7–31C shows the adnexal ring next to the ovary. Fig. 7–31D shows the surgical findings of ectopic pregnancy via laparoscopic surgery.
FIGURE 7–31A. Sagittal sonogram of the right upper quadrant with free-fluid in Morison’s pouch.
FIGURE 7–31B. Transabdominal sagittal sonogram of the uterus free of any intrauterine pregnancy.
FIGURE 7–31C. Transabdominal sagittal scan of a left adnexa with an adnexal ring next to the left ovary.
FIGURE 7–31D. Laparoscopic findings of left ectopic pregnancy.
The treatment for ectopic pregnancy depends on whether the pregnancy is ruptured or unruptured, size, location, and the patient’s clinical condition. The use of methotrexate, which is a folic acid antagonist that inhibits DNA synthesis in the trophoblastic cells, has been successfully used in treatment of unruptured ectopic pregnancy.10
Medical treatment with methotrexate is very useful when the pregnancy is located in the cervix, tube, or ovary, or where surgical treatment carries a significant risk.10 The purpose of medical treatment is to avoid potential risk of both anesthesia and surgery and spare the fallopian tube from surgical trauma or damage from spontaneous rupture. The success rate is high if the unruptured gestational sac is <4 cm and no sonographic evidence of fetal heart activity.10 This medical treatment is not without failure. There is a possibility of rupture in 3–4% of medically treated cases.3, 5, 10
Patients with ruptured ectopic pregnancy usually present with severe pain, accompanied by hypotension, tachycardia, and rebound tenderness. Blood normally clots after rupture and is sonographically characterized as echogenic free-fluid. Fig. 7–32 demonstrates an ectopic gestational sac with a small embryo in the sac and echogenic free-fluid in the posterior cul-de-sac secondary to leaking hemorrhage. Sonographers should be aware that before rupture, the pain increases in severity and then decreases in its severity after rupture. The pain then recurs after rupture, as generalized abdominal pain or right-upper-quadrant (RUQ) pain with rebound tenderness secondary to hemoperitoneum. Sonographers must be informed before performing an ultrasound of any history of ectopic pregnancy that is currently or previously treated with methotrexate. In a patient in which methotrexate has failed and the patient is hemodynamically unstable, ultrasound scanning may not be helpful because a delay in surgical management could result in the patient going into shock.
FIGURE 7–32. Transvaginal sagittal scan of the right adnexa with an ectopic gestational sac with a small embryo. Echogenic free-fluid is seen next to the gestational sac.
Laparoscopic salpingostomy or partial salpingectomy are currently the surgical procedures of choice for ectopic pregnancy when methotrexate is not advised, except for cornual ectopic pregnancy, which in most cases requires a cornual resection via laparotomy1, 10 Laparotomy is indicated when patients are hemodynamically unstable or when laparoscopic surgery could be a significant risk.14 Sonographers should obtain some past surgical history, if not included on the sonogram request form. Did you have an ectopic pregnancy before? Was your fallopian tube removed? On which side was your previous ectopic pregnancy? Sonographers should be alert for any abdominal and pelvic surgical scars, which may be a result of previous surgical removal of abdominal/pelvic viscera. Failure to be observant and to obtain patient history pertinent to scanning could result in misdiagnosis.
Salpingostomy: surgical incision of the fallopian tube for removal of tubal pregnancy. The incision is left open. The fallopian tube is not removed.
Salpingotomy: surgical incision of the fallopian tube for removal of tubal pregnancy. The incision is closed by suture. The fallopian tube is not removed.
Salpingectomy: surgical removal of tubal pregnancy by removing part or all of the fallopian tube.
FIRST TRIMESTER OBSTETRICS
Pregnancy is divided into three equal trimesters:
• First trimester: 0–13 weeks
• Second trimester: 13–28 weeks
• Third trimester: 28–42 weeks
Documentation of intrauterine pregnancy can be made as early as 4 weeks with transvaginal sonography by the identification of a gestational sac within the uterus. The gestational sac at this time has an anechoic center that represents the chorionic fluid and a highly echogenic ring that represents the developing chorionic villi and decidual tissue (chorion-decidua capsularis). The gestational sac size is about 5 mm when first depicted and increases in size as pregnancy advances with a growth rate of 1 mm/day.3 The gestational sac is empty and free of an embryo or yolk sac at this early stage. The gestational age at this time can be predicted by measuring the mean sac diameter.
These measurements are obtained by longitudinal sac diameter, the anteroposterior diameter, and the transverse diameter of the chorionic cavity, excluding the surrounding echogenic ring. All the dimensions are added then divided by 3 to obtain the mean sac diameter.
At approximately 5 weeks gestational age, the lacunae structures can be seen in a semicircle on one side of the gestational sac in the choriodecidua and represent the beginning of uteroplacental circulation (intervillous spaces).8Sonographically, they appear as small rounded hypoechoic structures that measure about 2–3 mm. Transvaginal color Doppler can demonstrate blood flow in these spaces. The yolk sac is the first anatomic structure seen within the gestational sac at 5 weeks and measures approximately 5–6 mm.
The yolk sac lies in the chorionic cavity (the extra-embryonic coelom) between the amnion and chorion (Fig. 7–33). The functions of the yolk sac are as follows:
1. Form blood cells (hematopoiesis)
2. Give rise to sex cell (sperm and egg)
3. Supply nutrients from the trophoblast to the embryo
FIGURE 7–33. Yolk sac seen in the chorionic cavity and the embryo in the amniotic cavity.
Sonographically, the yolk sac can be depicted between 5 and 10 weeks of gestation. It is filled with vitelline fluid and appears anechoic on ultrasound. The sac is connected to the midgut by a narrow pedicle called the yolk stalk, vitelline duct, or the omphalomesenteric duct (Fig. 7–34). The yolk stalk detaches from the midgut by the end of the sixth week, and the dorsal part of the yolk sac is incorporated into the embryo as the primitive gut. As pregnancy advances, the yolk sac shrinks and becomes solid and its stalk becomes relatively longer.1 Fig. 7–35 illustrates an early pregnancy, yolk sac, and its surrounding anatomic structures.
FIGURE 7–34. Yolk sac with its connecting yolk stalk.
FIGURE 7–35. Early pregnancy with yolk sac and surrounding anatomic structures.
The yolk sac may prevail throughout the pregnancy and be recognized on the fetal surface of the placenta near the attachment of the umbilical cord; this situation is extremely rare and has no significance. In about 2% of adults, the proximal portion of the yolk stalk persists as a diverticulum of the ileum called Meckel’s diverticulum.1, 3, 10
Yolk Sac-Embryo Complex. At approximately 6 weeks of gestation, the crown-rump length of the embryo measures 3–5 mm and abuts the yolk sac. The heartbeat can be depicted at this time. The upper limbs buds appear first at 7 weeks, followed by the lower limb buds.
At approximately 8 weeks of gestation, the physiologic herniation of the midgut can be seen sonographically as a hyperechoic bulging of the cord near the point where the cord enters the fetal abdomen. The midgut returns to the abdomen, where it undergoes a second rotation, which is 180° counterclockwise.1, 10 Thus, the midgut undergoes a total rotation of 270°. If the bowel fails to return to the abdomen during this second stage of rotation, an omphalocele could be the result. Table 7–6 describes the chronological events of early pregnancy.
TABLE 7–6 • Chronological Chart: Transvaginal Obstetrical Sonography
Nuchal translucency refers to the space between the back of the neck and the overlying fetal skin. This anechoic space is produced by a collection of fluid under the skin. This finding is observed in all fetuses between the gestational ages of 11 to 13 weeks and 6 days15 (Fig. 7–36A). This should not be confused with a nuchal fold, which is measured from the outer edge of the occipital bone to the outer margin of the skin in the second and third trimesters. There is a strong association between the size of the translucency and chromosome abnormality, particularly the risk for Down’s syndrome (trisomy 21) and Turner’s syndrome.15
FIGURE 7–36A. Normal nuchal translucency.
FIRST TRIMESTER CYSTIC HYGROMA
Cystic hygroma is congenital lymphatic obstruction between the lymphatic and venous pathway resulting in lymphatic fluid accumulation in the lymphatic sac within the nuchal region. The sonographic appearance of cystic hygroma in the first trimester is different from the sonographic appearance in the second trimester. The first trimester sonographic appearance of cystic hygroma is characterized by excessive enlargement of nuchal translucency (Fig. 7–36B), which extends along the entire long axis of the embryo with or without septations. First trimester cystic hygromas are associated with trisomies, whereas second trimester cystic hygromas are associated with monosomy × (Turner’s syndrome).15 After the 14th week of gestation the nuchal translucency measurements is no longer feasible and the sonographic appearance of cystic hygroma is characterized by single or multiple septated masses of the fetal neck. Cystic hygromas occur in the neck in 80% of cases15 and occur in the axilla, thorax, and abdominal wall.16
FIGURE 7–36B. Nuchal translucency enlargement.
Sonographic measurements of Nuchal Translucency
Approximately 90% of nuchal translucency (NT) measurements less than 3 mm at 12 weeks are normal at birth, while 10 % have abnormalities.1 NT is a screening test and amniocentesis and chorionic villus sampling are diagnostic tests. This screening test is operator dependent, with the majority of errors occur because of incorrect digital calipers placement.17 (Correct and incorrect placements for digital calipers Fig. 7–37.) In order to reduce this error, the following are recommendations.
FIGURE 7–37. Correct and incorrect placements for digital calipers.
Guidelines for measurements:
• Only use the “+” calipers, others are less accurate. Take three measurements and record the maximum measurement (do not average).
• The CRL should be 45–84 mm (11–14 weeks).
• Measurement can be performed either by transabdominal or transvaginal.
• The fetus should be in the mid-sagittal plane.
• The fetal neck should be in a neutral position.
• The calipers should be placed perpendicular to the long axis of the fetus.
• The calipers should be placed from inner-to-inner borders.
• Distinguish between fetal skin and amnion.
The chronological development of the embryo and fetus during a pregnancy is described in (Table 7–7). The first trimester findings are imaged with TVS.
TABLE 7–7 • Embryological Development
FIRST TRIMESTER ABNORMALITIES
Hydatidiform Mole. This is the most common and benign component of gestational trophoblastic disease (abnormal proliferation of the trophoblastic elements) that may be partial or complete.
Complete—Sonographic findings are an enlarged uterine cavity filled with complex echoes often resembling placental tissue with multiple cystic vesicles Fig. 7–38A and B show a sonogram of the uterus with honeycomb appearance seen in cases of hydatidiform mole. Fig. 7–38C shows color and spectral Doppler of the uterus with hydatidiform mole.
FIGURE 7–38. (A and B) Sagittal and transverse sonograms with the uterine cavity filled with tiny grapelike tissue, giving the sonographic characteristic of hydatidiform mole. (C) Color and spectral Doppler of the uterus with hydatidiform mole. (D) Hydatidiform mole with septated theca lutein cyst on the left adnexa. (E) Gross specimen findings after suction and curettage, numerous hydropic villi.
Hydatidiform mole is associated with a markedly increased β-hCG and may have bilateral theca lutein cysts 18–30% of the time.10 Fig. 7–38D shows a theca lutein cyst with multiple septations next to uterus. Fig. 7–38E shows a pathology specimen off hydropic villi following evacuation of the uterus. If hydatidiform mole is not treated, this can progress into malignant choriocarcinoma.1, 3, 5, 10
Partial—The combination of a live or dead fetus and a localized area of placenta with molar degeneration. Ninety percent of partial moles are triploidy. On ultrasound, a partial mole presents as an enlarged hydropic placenta, with focal multicystic, anechoic spaces replacing the normal homogeneous appearance of placenta.10
Sonographic Appearance of Hydatidiform Mole
• Swiss cheese appearance
• Snowstorm appearance
• Vesicular sonographic texture
• Honeycomb appearance
Clinical Sign and Symptoms of Hydatidiform Mole
• Vaginal bleeding
• Uterus is larger than for expected gestational age
• Markedly elevated serum beta hCG
• Hyperemesis gravidarum
• Preeclampsia before 20 weeks of gestation
Blighted Ovum (Anembryonic Demise). This is a large (>2-cm) gestational sac without an embryo or yolk sac. The gestational sac is sometimes irregular in shape and fragmented with a thin choriodecidua. The serum β-hCG may fail to double or decline. The gestational sac fails to grow at increasing increments of 1 mm/day.3
Missed Abortion. This is an embryo without fetal heart motion retained in the uterus before 20 weeks. Fetal demise after 20 weeks is called an intrauterine fetal demise (IUFD). The serum β-hCG will decline with time.
SECOND AND THIRD TRIMESTER OBSTETRICS
Basic fetal cardiac evaluation has become an intricate component of obstetrical sonography. Fetal cardiac circulation is shown in Fig. 7–39. Note the three shunts present in fetal circulation that are not present after birth: (1) foramen ovale—between the left and right atria; (2) ductus arteriosus—between the pulmonary trunk and transverse aortic arch; and (3) ductus venosus—between the umbilical vein and inferior vena cava.18
FIGURE 7–39. Schematic drawing demonstrating fetal cardiac circulatory system. (Adapted with permission from Moore KL. The Developing Human: Clinically Oriented Embryology, 4, 8th ed, Philadelphia: WB Saunders, 2008.)
The basic cardiac evaluation should include the four chamber view and views showing the outflow tracts origin and relationship to each other. The inferior vena cava should also be visualized and a fetal heart rate recorded. Sixty-five percent of cardiac abnormalities can be detected from the four-chamber view. Eighty-five percent of defects can be detected if the great vessels views are included (Fig. 7–40).3, 10
FIGURE 7–40. (A) Sonogram demonstrating the four-chamber view (B) Schematic diagrams demonstrating the four-chamber view. (Reproduced with permission from Cyr DR, et al. A systematic approach to fetal echocardiography using real time two-dimensional sonography. J Ultrasound Med. 1986; Jun; 5(6):343–350.)
Gestational Age and Growth
Estimation of gestational age can be calculated using multiple parameters listed in Table 7–8. The fetal weight may then be plotted on a normal growth curve to assess the size of the fetus. Macrosomia describes a fetus that weighs more than 4,000 g. Large for gestational age (LGA) is a clinical term and refers to the fundal height of the uterus. LGA has many causes, such as a large fetus (>90th percentile), excessive amniotic fluid, fibroids, twins, or a molar pregnancy. Macrosomia is often a manifestation of insulin-dependent diabetes mellitus (IDDM). It is associated with increased muscle mass and fat, leading to an increased AC and thickened shoulders. As well as a large fetus, there is often increased amniotic fluid volume (AFV) and a decreased HC/AC ratio because of the large AC. A macrosomic fetus is at risk for shoulder dystocia, humeralclavicle fractures, meconium aspiration, prolonged labor, and asphyxial injury. Macrosomia carries an increased perinatal mortality, thus making its diagnosis by ultrasound important.2
TABLE 7–8 • Gestational Age and Range of Error
Intrauterine growth restriction (IUGR), is defined by ultrasound as a weight <10th percentile. Other measurement findings with IUGR are an increased HC/AC and FL/AC ratios, oligohydramnios (a decrease in amniotic fluid), and advanced placental grade. Symmetrical IUGR refers to overall growth restriction, whereas asymmetrical IUGR refers to the abdomen measuring smaller than normal for the gestational age and increasing the HC/AC and FL/AC ratios. In asymmetrical IUGR, blood is shunted to the brain in a brain-sparing effort and taken away from the bowel. Early onset IUGR with oligohydramnios is suggestive of a chromosomal abnormality or infection. Other causes of IUGR may be related to placental insufficiency. Maternal conditions that can be associated with IUGR include hypertension, vascular disease, autoimmune disease, and poor nutrition. Pulsed Doppler sonography may aid in assessing fetal well-being in addition to serial scans, AFV assessment, biophysical profile (BPP), and nonstress testing. When there is good umbilical cord blood flow, the waveform (systolic/diastolic ratio) demonstrates continuous diastolic flow.3, 10 An increased systolic/diastolic ratio of the umbilical artery suggests an increased resistance in the placenta, leading to a decrease in blood velocity and volume.3 The compromised fetus may demonstrate pulsatile or reversed flow in the umbilical vein, another sign of increased resistance to forward blood flow from the placenta to the fetus and a sign of cardiac compromise. Color Doppler sonography (CDS) may be used to sample the middle cerebral artery and the ductus venosus. Doppler interrogation of these sites is crucial in identifying the fetus that is at high risk of severe compromise. In the severely compromised fetus, the increased flow to the brain is evidenced by increased diastolic flow in the middle cerebral artery. In addition, flow may be shunted away from the liver resulting in ductus venosus flow.10
Color Doppler sonography (CDS) can be used to assess flow in the maternal uterine artery as it branches from the internal iliac artery. Sampling at this point typically reveals a waveform with a diastolic notch. This notch should not be present after 26 weeks, and when it is, it may indicate faulty placentation and a tendency to have pregnancy-induced hypertension (PIH) or IUGR.3, 10
Real-time sonography is vital to determine fetal condition, as evidenced by physiologic activities seen in fetal “breathing” and body movements. The compromised fetus may exhibit decreased or absent body movement and “breathing.” Hypoxia affects certain neurologic autonomic centers in reversed order to their maturation. For example, the central nervous center for body movement and “tone” develops early in fetal maturation followed by centers for cardiac rate variation and “breathing.” However, one of the first abnormalities to develop in the hypoxic fetus is lack of fetal heart rate acceleration followed by decreased fetal breathing and body motion.
The standard nonstress test (NST) evaluates changes in heart rate when the fetus moves. A negative (reactive) NST has high negative predictive value, but false positives arise and are distressing for the new mother and her physician.
The biophysical profile incorporates the NST, amniotic fluid, fetal breathing, and body movements (both gross and tone). Each component is given a score of 2 if present, 0 if absent, with 10 being the highest score. Some biophysical profiles do not include the NST, with 8 being the highest score.
The Doppler techniques mentioned above may also be included in assessing fetal well-being. Thus, there are several sonographic techniques to monitor fetal well-being.3
Fetal demise is defined as death of the developing fetus after 20 weeks of gestation. The clinical and sonographic signs for fetal demise are numerous. The sonographic signs can be divided into specific and nonspecific. The specific signs are: (1) the failure to find the fetal heart tones on Doppler examination, (2) no fetal cardiac motion on M-mode, and (3) no movements or fetal heart pulsation seen on real-time sonography. The nonspecific signs are:
• Overlapping of the fetal sutures (Spalding’s sign)
• Hydramnios or oligohydramnios
• Flattened (oblong) fetal head
• Absence of the falx cerebri
• Distorted fetal anatomy
• Decrease in the biparietal diameter when measurements are repeated from 1 week to the next
• Decrease in the size of the uterus
• Edematous soft tissue around the head (the “halo” sign or Druel’s sign)
• Fragmentation of the fetal skin
• Diffuse edema of the entire fetus (anasarca)
• Separation of the amnion from the chorion after 20 weeks
• Gas in the fetal circulatory system (Robert’s sign)
• Hydropic swelling of the placenta
The clinical and laboratory findings of fetal demise are the failure of the uterus to grow, two negative pregnancy test results (serum β-hCG), no fetal movement, no heart sounds on auscultation, and red or brown amniotic fluid.14Fig. 7–41 illustrates the overlapping of the fetal cranial bones at the skull sutures and scalp edema.
FIGURE 7–41. Spalding’s and Druel’s signs.
Amniotic fluid has many functions. It protects the fetus from trauma, allows for growth, controls temperature, allows for respiration, allows for normal gastrointestinal and musculoskeletal development, and prevents infection by its antibacterial properties. In the first trimester, amniotic fluid is made by the placenta. After 12 weeks, the primary sources of amniotic fluid are the fetal kidneys, lungs, and skin. Fluid is re-accumulated in the body through fetal swallowing. Amniotic fluid volume (AFV) normally increases until 33 weeks of gestation. It peaks and then begins to decline for the remainder of the pregnancy.1, 3, 10 An exact volume of AFV cannot be obtained with ultrasound; however, the amniotic fluid index (AFI) is an indirect means of quantifying the amount of amniotic fluid. The maternal abdomen is divided into four quadrants. In each quadrant, an anteroposterior measurement of amniotic fluid is taken that does not contain body parts or umbilical cord. The four quadrant values are totaled, with the sum representing the AFI. The AFI can be compared to a normal AFI curve to assess AFV Another means of measuring amniotic fluid is the single pocket measurement. The largest pocket of AF that does not contain body parts or umbilical cord is measured in an anteroposterior dimension. If a single deepest pocket of amniotic fluid measures between 0 to 2 cm, then the diagnosis of oligohydramnios can be made.3, 14 The single pocket measurement is less reliable than the AFI, but it can be useful in such situations as multiple gestations and pre-decompression and post-decompression amniocentesis.
Oligohydramnios is the decrease of AFV below the 2.5th percentile. It may be caused by a renal abnormality or obstruction, placental insufficiency, premature rupture of membranes, or post dates. Oligohydramnios with placental insufficiency is caused by a decreased blood flow to the uterus, which in turn, causes decreased renal perfusion.5 A lack of AFV can contribute to pulmonary hypoplasia and extremity contractures. The mnemonic DRIPP serves as a key for memorizing the five more common conditions associated with oligohydramnios:
• D demise (polyhydramnios immediately after death due to absence of fetal swallowing, followed by oligohydramnios due to fetal absorption of fluid)
• R renal agenesis
• I intrauterine growth restriction (IUGR)
• P premature rupture of membranes (PROM)
• P postmaturity
Polyhydramnios is the excessive accumulation of AFV, measuring more than 95th percentile. Sixty percent of polyhydramnios are idiopathic, 20% are structural, and 20% are maternal (IDDM).1, 3
Placenta and Umbilical Cord
The placenta is responsible for the maternal/fetal exchange of nutrients, oxygen, and waste. The placenta can attach anywhere in the uterus. The fetal side consists of a fused layer of amnion and chorion, with underlying vessels being located in the chorionic villi. The maternal component consists of cotyledons, composed of maternal sinusoids and chorionic villous structures. Oxygenated maternal blood enters the intervillous spaces that bathe the chorionic villi. Gases and nutrients are exchanged across the walls of the villi, with waste crossing from inside the villi to the intervillous space for the maternal vessels to transport away from the placenta. Maternal blood flow increases in pregnancy to accommodate the increased demand of the placenta. The placenta is a low resistive organ that allows a decrease in resistance to the fetus as the fetus grows.1 This results in progressively increasing blood flow as the pregnancy advances. Placental insufficiency is related to increased resistance in the vascular bed and results in decreased blood flow to the fetus. Placental insufficiency may be indirectly monitored by umbilical cord pulsed Doppler. The ratio of systolic flow to diastolic flow will show the amount of resistance in the placental bed. A lower ratio is less resistive; a higher ratio is more resistive. Normal ratios vary with gestational age and tables are available listing the normal ranges.
Placenta previa is the condition in which the placenta crosses the internal os of the cervix. Placenta previa is the primary cause of third trimester bleeding, although bleeding may occur from previa at any time in pregnancy.1Placenta previa may be further subcategorized into (1) complete—placenta totally covers the internal os; (2) partial—placenta is over the edge but does not cross the internal os; (3) marginal—placenta touches the edge of the internal os; and (4) low lying—the placenta is within 2 cm of the internal os. The clinical finding in placenta previa is painless vaginal bleeding. Bladder distention and myometrial contraction can distort the lower uterine segment and give a false image of placenta previa. Post void images helps to avoid this technical error. Placentas may have a succenturiate or accessory lobe that is connected to the main lobe of the placenta by blood vessels within a membrane. If these vessels cross the internal os it is considered a vasa previa.1, 3
Placental abruption is the premature separation of the placenta from the uterine wall after 20 weeks of gestation. Symptoms may include painful vaginal bleeding and abdominal pain or cramping. Although the diagnosis is usually made clinically, sonographic findings are a retroplacental, hypoechoic area composed mainly of veins >2 cm, and large periplacental hematomas. Hematoma appearances vary with acute being from hyperechoic, becoming isoechoic, and finally becoming hypoechoic to anechoic. Placental abruption is one of the leading causes of perinatal mortality and accounts for 15–20% of all perinatal deaths. It can be associated with maternal vascular disease, hypertension, abdominal trauma, cocaine abuse, cigarette smoking, advanced maternal age, and unexplained increased MSAFP.1
Placenta accreta is the abnormal adherence of placental tissue to the uterus. It is divided into (1) placenta accreta placental attachment to the myometrium without invasion; (2) placenta increta—invasion of the placenta into the myometrium; and (3) placenta percreta—invasion of the placenta through the uterus and often invasion into the bladder or rectum. Risk factors include uterine scarring from cesarean sections and advanced maternal age.1Implantation sites at risk are uterine scars, submucous fibroid, lower uterine segment, rudimentary horn, and uterine cornua. With placenta accreta, the normal hypoechoic 1–2 cm myometrial band is absent or thinned (<2 mm) with loss of placental/myometrial interface.5, 10 There may be large hypoechoic to anechoic spaces in the placenta, termed “Swiss cheese appearance.” Placental vascularity is also increased.5 Doppler ultrasound is used to aid in the sonographic diagnosis.
Chorioangioma is the most common benign tumor of the placenta. It is a vascular malformation arising from the chorionic tissue that appears as a well-defined, hypoechoic mass near the chorionic surface and often near the cord insertion site.3 Color and pulsed Doppler will confirm the increased vascularity of this lesion.
The umbilical cord consists of two arteries and one vein. The vein enters the fetus and drains into the ductus venosum and left portal vein in the liver. The umbilical vein carries oxygenated blood. The umbilical arteries, carrying deoxygenated blood, are seen coursing laterally around the bladder as they leave the fetal body. The vessels in the cord are surrounded by Wharton’s jelly for protection. The umbilical cord normally inserts into the central portion of the placenta. It can, however, insert eccentrically or near the membranes. It can also be a velamentous insertion when it inserts into the membranes and courses through the membrane to the placenta.3, 5 Both of these insertions can play a part in placental insufficiency and fetal growth. Occasionally, only one artery will be present resulting in a two vessel umbilical cord. It may be associated with other abnormalities and could possibly affect fetal growth, although not common. Color Doppler Sonography can help identify absence of the umbilical artery, as well as nuchal cord and cord knots.5
Fetal Head, Neck, and Spine
Neural Tube Defect. This is a spectrum of malformations of the neural tube including: (1) anencephaly, (2) spina bifida, and (3) cephalocele. Folic acid taken daily before and during pregnancy is known to reduce the risk of neural tube defect.1
Anencephaly. This is the most severe form of neural tube defect. It is characterized by absence of the upper portion of the cranial vault and underlying cerebral hemispheres. The fetal face and brainstem are normally present in anencephaly. It may be diagnosed as early as 12 weeks by transvaginal sonography and is associated with a markedly increased MSAFP, polyhydramnios, spinal defects, and bulging of the fetal orbits, giving the fetus a frog-like appearance.19
Spina Bifida. This is a defect in the lateral processes of the vertebrae allowing the spinal canal to be exposed, which in turn disrupts the muscle and skin covering. Herniation can be limited to meninges (meningocele) or involve the neural tissue as well (myelomeningocele). The most common sites of spina bifida are lumbar, lumbosacral, and thoracolumbar. Cranial findings associated with spina bifida are (1) “banana sign,” consistently present with a defect (99%), and (2) “lemon sign.” The banana sign is the displacement of the cerebrum inferiorly and the cisterna magna is usually obliterated. On the transverse view, the cerebellum resembles a banana instead of its characteristic view. The lemon sign includes bilateral depression of the frontal bone and gives the sonographic impression of a “lemon”-shaped head (Fig. 7–42 A and B). Spina bifida is often associated with increased MSAFP, ventriculomegaly, and clubfeet.1, 3, 19
FIGURE 7–42 (A) Lemon. (B) Sonogram of a “lemon”-shaped head.
Cephalocele. This is a protrusion of the cranial contents through a bony defect in the skull. An encephalocele contains brain tissue. The majority are occipital (75%).3, 19 They often cause blockage of cerebrospinal fluid and ventriculomegaly results. Very large defects may be associated with microcephaly. Both types have a poor prognosis.3, 19
Ventriculomegaly. The anatomy of the ventricular system is imperative in order to recognize the normal and abnormal sonographic appearance (Figs. 7–43A and B). This is enlargement of the lateral ventricles, more than 10 mm in the atrial diameter. In the absence of a spinal defect, pronounced ventriculomegaly (>15 mm) is most commonly associated with an obstruction of the ventricular system. In order of occurrence, these obstructions are aqueductal stenosis, communicating hydrocephalus, and Dandy-Walker malformation. Congenital hydrocephaly is an X-linked abnormality with only males affected and females being carriers. If there is a strong family history, DNA testing is available.3, 19 Ventriculomegaly is often associated with other abnormalities.
FIGURE 7–43A. Diagram of the ventricular system in the lateral view.
FIGURE 7–43B. Diagram of the ventricular system in the superior view.
Dandy-Walker Malformation. This consists of a splaying of the cerebellar vermis, dilated fourth ventricle, increased cisterna magna (>10 mm), and ventriculomegaly. It can be associated with chromosomal abnormalities and is frequently associated with such other cranial midline defects as agenesis of the corpus callosum. It is often associated with other system abnormalities as well.3
Holoprosencephaly. This is a group of midline defects resulting from incomplete cleavage of the prosencephalon. The three major varieties are (1) alobar—single rudimentary ventricle, absent cerebral falx, fused thalamus, absent third ventricle. Facial findings may range from cyclopia to severe hypotelorism. A medial cleft lip/palate is common. A proboscis may replace the nose or the nose may be very flattened; (2) semilobar—the cerebral hemispheres are partially separated posteriorly, with partial separation of the lateral ventricles. Both alobar and semilobar holoprosencephaly are associated with microcephaly; (3) lobar—almost complete separation of cerebellum and ventricles except for the fused anterior horns of the lateral ventricles. Other sonographic findings are absent cavum septum pellucidum. Facial findings are less severe than those found with alobar or semilobar holoprosencephaly.3
Cystic Hygroma. This most often occurs at the posterior neck. A hygroma is a sac filled with lymphatic fluid caused by an obstruction of the lymphatic system. It may be multiloculated or contain a midline septum and is often associated with Turner’s syndrome or Down’s syndrome.19
Fig. 7–44A shows a longitudinal sonogram of fetal neck with cystic hygroma. Fig. 7–44B shows a Transverse sonogram of the same case demonstrating multiple septations in the mass.
FIGURE 7–44A. Longitudinal sonogram of the fetus with cystic hygroma in the posterior region of the fetal neck.
FIGURE 7–44B. transverse sonogram of the same case demonstrating the multiple septations in the mass.
Choroid Plexus Cyst. This is a cyst in the choroid plexus of the lateral ventricles. With other sonographic findings, it may be associated with trisomy 18 or 21. Alone, many investigators consider this a normal anatomic variant.3, 10
Iniencephaly. This is a defect in the occiput involving the foramen magnum characterized by marked retroflexion of the fetal head and frequently shortened spine. This is a rare finding and has a strong association with other abnormalities.3
Agenesis of the Corpus Callosum. The corpus callosum begins to develop at 12 weeks of gestation and its development is complete at approximately 20 weeks.19 This abnormality cannot be diagnosed until after 18 weeks of gestation. Findings to aid in diagnosis include: (1) absence of the cavum septum pellucidum (2) enlargement of the posterior horn of the lateral ventricle (3) Extremely narrow frontal horns (4) enlargement and upward displacement of the third ventricle. Agenesis of the corpus callosum has a strong association with other abnormalities.3, 10, 19
Hydranencephaly. This is a severe destructive process, believed to result from occlusion of the internal carotid arteries. The cerebral cortex is replaced by fluid, causing macrocephaly. The thalamus, brainstem, and cerebellum are spared.3, 10
Vein of Galen Aneurysm. This is an arteriovenous malformation in vein of Galen located posterior to the third ventricle in the midline. Color and pulsed Doppler will demonstrate high-velocity arterial and venous blood flow. This is associated with congestive heart failure and hydrops.10
Cleft Lip/Palate. Isolated cleft lip and/or palate is the most common congenital facial anomaly. Lateral cleft lip is commonly isolated. Medial cleft lip is associated with chromosomal abnormalities.10
Atrial/Ventricular Septal Defect. This is a congenital malformation of the septum that appears as an opening between the chambers. It is the most common cardiac defect, accounting for 26% of defects.20
Atrioventricular Canal Defect. This is also known as atrioventricular septal defect, or endocardial cushion defect. A complete defect has a single ventricle, a single atrium, and a single atrioventricular valve. This appearance may vary with partial defects of the atrial or ventricular septums. This is the most common cardiac defect in trisomy 21.20
Hypoplastic Left Heart Syndrome. This is hypoplasia of the left ventricle, atrium, mitral valve, and aortic outflow. The right side of the heart will be enlarged.20 The appearance vary with different degrees of severity.
Coarctation of the Aorta. This is a narrowed segment of aorta along the aortic arch. It is difficult to see the narrowing but may present as a milder form of hypoplastic left heart syndrome later in pregnancy. Pulsed Doppler studies may also show a decrease in blood flow in the proximal portion of the aorta.20
Tetralogy of Fallot. This presents with the following defects: (1) ventricular septal defect, (2) overriding aorta, (3) pulmonary stenosis or atresia, and (4) right ventricular hypertrophy. It has a strong association with chromosomal abnormalities.19, 20
Ebstein’s Anomaly. This is the inferior displacement of the tricuspid valve. The right atrium is enlarged, and the valve, which is commonly abnormal, may appear thick and irregular in motion. Tricuspid valve regurgitation is often appreciated.20
Double Outlet Right Ventricle. The pulmonary artery and aorta both originate from the right ventricle, giving the appearance of the great vessels running parallel. Often a ventricular septal defect is present.20
Transposition of the Great Vessels. The aorta arises from the right ventricle, and the pulmonary artery arises from the left ventricle. The great vessels appear parallel on ultrasound. The pulmonary bifurcation and brachiocephalic vessels must be identified to correctly diagnosis this entity. Atrial septal defect and ventricular septal defect are often present.3, 20
Truncus Arteriosus. This is a single large ventricular outflow tract overriding a ventricular septal defect. Right ventricular outflow tract will not be visualized, and pulmonary artery branches as well as aortic branches will be seen arising from the truncus.20
Rhabdomyoma. This is the most common intracardiac tumor. It can be multiple and appears as an echogenic mass located anywhere within the cardiac system. It is not visualized <22 weeks and has a strong association with tuberous sclerosis.20
Supraventricular Tachycardia. The fetal heartbeat is more than 200 bpm. Both supraventricular tachycardia and atrial flutter can lead to cardiac failure because of increased cardiac output.20
Congenital Diaphragmatic Hernia. This is a congenital defect in the diaphragm allowing abdominal contents to herniate into the thorax. It may be left sided (75–90%), right sided (10%), or bilateral (<5%). Sonographically, (1) the fetal heart may be deviated, (2) stomach or bowel may be visualized in the thorax, (3) the area adjacent to the heart may appear inhomogeneous, and (4) polyhydramnios may be present. The intrathoracic abdominal contents can cause pulmonary hypoplasia, a significant factor in the high perinatal mortality (50–80%) of this disorder. If the liver is intrathoracic, congenital diaphragmatic hernia has a poorer prognosis (43% survival) versus an intra-abdominal liver (80% survival). Associated anomalies (15–45%) and chromosomal abnormalities (5–15%) will also affect perinatal survival.19, 20
Congenital Cystic Adenomatoid Malformation. This is the most frequently identified mass in the fetal chest. It is typically unilateral and has three types: (1) type I, macrocystic—multiple large cysts measuring 2–10 cm, (2) type II—multiple medium-sized cysts <2 cm, and (3) type III, microcystic—sonographically appearing as a solid, homogenous echogenic lung mass. Many congenital cystic adenomatoid malformations spontaneously regress in size during the third trimester. Prognosis is dependent on size, degree of mediastinal shift, and presence or absence of hydrops and polyhydramnios. Types I and II typically have a better prognosis.20
Pulmonary Sequestration. This is a solid, nonfunctioning mass of lung tissue that lacks communication with the tracheobronchial tree. It has its own blood supply commonly arising directly from the aorta and is fed by a single vessel. The majority are visualized as well circumscribed masses in the left lower lung base. They may cause mediastinal shift and hydrops. Ten percent can be found below the diaphragm and should be considered with any suprarenal mass in the left abdomen. Fifty percent to seventy-five percent of sequestrations regress spontaneously.20
Pleural Effusion. This is an abnormal accumulation of fluid in the pleural lining of the fetal thorax. The etiologies are hydrops fetalis, chromosomal, and fetal infection. Fig. 7–45 shows a transverse sonogram of the fetal thorax with bilateral pleural effusions.
FIGURE 7–45. Transverse sonogram of a fetus with bilateral pleural effusions.
Esophageal Atresia. This is an incomplete formation of the esophagus. There are five types of atresia, with 90% of those having a tracheoesophageal fistula that communicates with the fetal stomach. Sonographically, the exam may be normal or there may be a small to absent stomach bubble and polyhydramnios. Even with a stomach bubble visualized, this must be considered normal with unexplained polyhydramnios. This has a strong association with other anomalies and chromosomal abnormalities.20
Duodenal Atresia. This is a partial to complete obstruction caused by the failure of recanalization of the duodenum. It is the most common perinatal intestinal obstruction. The stomach and duodenum fill with fluid proximal to the site of the obstruction creating the classic “double-bubble” sign. Fifty percent are associated with other findings including growth restriction, polyhydramnios, gastrointestinal, and cardiac anomalies. Duodenal atresia has a strong association with trisomy 21.3, 10
Gastroschisis. This is an anterior abdominal wall defect, most commonly to the right side of the umbilicus, which allows herniation of abdominal contents into the amniotic cavity. The most common finding is free-floating bowel in the amniotic fluid, but stomach and bladder may also herniate into the amniotic fluid. Exposure to amniotic fluid and compression at an abdominal wall can lead to dilation and edema of the bowel. Overall, this has a good prognosis and does not have a strong association with chromosomal defects or other anomalies. It is associated with an elevated MSAFP.3
Omphalocele. This is a midline defect in the anterior abdominal wall with herniation of abdominal contents into the base of the umbilical cord. The mass is covered by a membrane and may not always have an elevated MSAFP, or may not elevate the MSAFP as significantly as gastroschisis. The umbilical cord can be seen inserting into the abdominal mass. Omphaloceles commonly contain liver but may contain other abdominal organs such as bowel. They have a strong association with other anomalies (50–80%), particularly cardiac, as well as chromosomal abnormalities (40–60%). If the omphalocele is small and contains only small bowel, the risk of aneuploidy increases.2
Pentalogy of Cantrell. This is an extensive defect of the thoracoabdominal wall characterized by (1) ectopia cordis, (2) omphalocele, (3) ventricular septal defect, (4) defect of the sternum, and (5) diaphragmatic hernia. This anomaly is sonographically distinctive because of an omphalocele and ectopia cordis. There are many other associated craniofacial abnormalities, and it often is associated with chromosomal abnormalities.19, 20
Beckwith-Wiedemann Syndrome. This is a group of disorders including omphalocele, macroglossia, organomegaly, hypoglycemia, and hemihypertrophy.3
Cloacal Exstrophy. This is an association of anomalies including omphalocele, herniated, fluid filled structure inferior to omphalocele in place of urinary bladder, imperforate anus, and neural tube defect. This defect has a marked increased MSAFP20
Meconium Ileus. This is the third most common cause of neonatal bowel obstruction. Sonographic findings include echogenic small bowel, dilated fluid-filled loops of bowel, and echogenic dilated bowel. It has a strong association with cystic fibrosis. If the internal diameter of the small bowel is more than 7 mm, it is suggestive of obstruction.1, 3
Meconium Peritonitis. This is a reaction to bowel perforation. Meconium causes a peritoneal reaction that forms a membrane, which seals the perforation and may be seen as a thick-walled cyst. Other findings are ascites and meconium calcifications.1, 3, 19
Limb-Body Wall Complex (LBWC). This is a complex set of abnormalities caused by failure of the anterior abdominal wall to close. Findings include complete body wall defects, absence of umbilical cord, severe scoliosis, and lower limb abnormalities. Abnormalities are widespread and appearance may be a mass of tissue with few distinctive features.3, 19
Amniotic Band Syndrome. Rupture of the amnion early in pregnancy resulting in formation of amniotic strands that stick and entangle fetal parts resulting in amputation of digits, arms, and legs. Fetal movement restriction due to amniotic bands is helpful for the sonographic diagnosis.3, 19
Hydrops. There are two types: (1) non-immune—accumulation of fluid in body cavities (pleural, pericardial, and peritoneal) and soft tissue. There are many causes for this entity, but major causes are cardiac failure, anemia, arteriovenous shunts, mediastinal compression, metabolic diseases, fetal infections, fetal tumors, congenital fetal defects, chromosomal and placental anomalies; (2) immune—sonographic findings are the same. These are caused by maternal antibodies destroying fetal red blood cells, which ultimately leads to erythroblastosis fetalis or congestive heart failure.2
Fig. 7–46 A, B, and C are sonograms demonstrating fetal hydrops, bilateral pleural effusions, and polyhydramnios, respectively
FIGURE 7–46. (A, B, C) Sonograms demonstrating fetal hydrops, bilateral effusions, and polyhydramnios.
Ascites. This is free fluid within the abdominal cavity. It may be part of the hydrops complex or isolated because of bowel perforation or bladder perforation.
Situs Inversus Totalis. This is complete thoracic and abdominal organ reversal. Partial situs involves the abdominal organs only. Often associated with polysplenia and congenital heart defects.2
Abdominal Cyst. The differential for an isolated abdominal cyst not related to the GI or GU tract include ovarian cyst, mesenteric cyst, omental cyst, or urachal cyst as the most common listings.
Ureteropelvic Junction Obstruction. This is an obstruction at the junction of the renal pelvis and ureter. It is the most common cause of hydronephrosis. A complete obstruction will lead to massive hydronephrosis eventually causing dysplasia.
Ureterovesical Junction Obstruction. This is an obstruction at the junction of the ureter and bladder. Sonographic findings include mild hydronephrosis and hydroureter. Often associated with duplicated renal anomalies including the ureter. The abnormal ureter commonly has a stenotic opening into the bladder and forms an ureterocele, which appears as a cystic structure within or adjacent to the bladder.
Posterior Urethral Valve Bladder Outlet Obstruction. This is an obstruction of the posterior urethral valves. Overwhelming found in males, the bladder is massively dilated with hydroureters and hydronephrosis. The massive hydronephrosis may lead to atrophy of the kidneys. Anhydramnios is present with complete obstruction. On ultrasound, the bladder has the characteristic “keyhole” appearance as urine fills the proximal urethra. The abdominal wall becomes overly distended, which results in prune belly syndrome (abnormal development of abdominal musculature leading to a lax abdominal wall in newborns). The lack of amniotic fluid causes Potter facies (flattened facies, low set ears) and flexion contractures of the extremities. Pulmonary hypoplasia, caused by anhydramnios, is the primary cause of neonatal death in this syndrome.
Renal Agenesis. Diagnosis is made by the following findings: anhydramnios to severe oligohydramnios, nonvisualized bladder, and absent kidneys without evidence of renal blood flow. The adrenal glands appear flattened and elongated, which may aid in the diagnosis.
Multicystic Dysplastic Kidney. This is an obstruction in the first trimester that leads to atretic kidneys and formation of randomly positioned and varying sized cysts in the parenchyma of the kidney. The parenchyma is usually increased in echogenicity as well.
Autosomal Dominant Polycystic Kidney Disease. There must be one affected parent for this disorder to occur. Findings are not always seen in pregnancy and if so, typically do not appear until third trimester. Kidneys may appear enlarged and echogenic with multiple large cysts.
Autosomal Recessive Polycystic Kidney Disease. This is also known as infantile polycystic kidney disease. Multiple microscopic cysts give the appearance of very large, echogenic kidneys with decreased AFV after 20 weeks. Findings may be normal <20 weeks.
Congenital Mesoblastic Nephroma. This is a rare renal tumor that sonographically appears as a large, solid, well-circumscribed, highly vascular mass. The increased vascularity can cause cardiac overload and polyhydramnios.
Neuroblastoma. This malignant tumor is commonly found in the adrenal gland. Sonographically, it appears as an echogenic, heterogeneous, suprarenal mass.19, 20
Limb shortening may be described as: (1) rhizomelic—shortening of the proximal limb, (2) mesomelic—shortening of the forearm bones or lower leg bones, (3) micromelia—shortening of all portions of the limbs, both severe and mild. There are many types of short limb syndromes, and the more common lethal and nonlethal varieties are discussed in this review.
Short limb syndromes are considered lethal if the thoracic circumference is less than fifth percentile for the gestational age, suggesting pulmonary hypoplasia. Other findings are: (1) severe micromelia, less than four standard deviations of mean, and (2) identification of such specific features as severe fractures.
Thanatophoric Dysplasia. This is the most common skeletal dysplasia and is uniformly lethal.
• Cranium—macrocrania, hydrocephaly, frontal bossing, cloverleaf shaped skull, depressed nasal bridge
• Thorax—severely hypoplastic giving the “bell-shaped” appearance, short ribs
• Bones—severe rhizomelia with bowing (“telephone receiver”); hypomineralization; spinal column appears narrow; polyhydramnios
Achondrogenesis—Type I, Most Severe. This exhibits severe micromelia, protruding abdomen, poor skull, and vertebral ossification. Type II, accounts for 80%.
• Thorax—shortened trunk
• Bones—severe micromelia with bowing and decreased mineralization
Osteogenesis Imperfecta Type II—Lethal. 01 type II is subcategorized into three types, but all three are discussed in general terms for this text.
• Thorax—bell shaped, with small thorax; ribs have multiple fractures, may appear thin and flared
• Bones—micromelia; may see fractures or bones may appear thickened, irregular, and bowed because of fractures folding on themselves
• Decreased fetal movement and polyhydramnios
Heterozygous Achondroplasia. This is the most common form of genetic skeletal dysplasia. It may not always be identified before <27 weeks.
• Cranium—increased HC, frontal bossing, depressed nasal bridge
• Bones—mild to moderate rhizomelic shortening, “trident” hand
Osteogenesis Imperfecta-Types I, III, IV
• Type I—may not identify <24 weeks; mild micromelia and bowing; may see isolated fractures
• Type III—will show lagging long bone growth early with mild to moderate shortening and bowing
• Type IV—similar to type I
Asphyxiating Thoracic Dysplasia (Jeune Thoracic Dystrophy)
• Thorax—may appear bell shaped
• Bones—mild to moderate micromelia (rhizomelic) with possible bowing, possible polydactyly polyhydramnios.
Multiple pregnancies account for 3.3% of live births. Dizygotic, or fraternal, twins occur when two separate ova are fertilized. Monozygotic, or identical, twins occur when a single ovum divides. Seventy-five percent of twins are dizygotic, and 25% are monozygotic. The frequency of monozygotic twinning is constant and occurs in 1:250 births. Dizygotic twinning varies widely and is dependent on race, maternal age, parity (increased risk with increased parity), maternal family history, and infertility medication.1
It is very important to determine the number of chorionic and amniotic sacs in twin pregnancies. The best and most accurate time to assess this is in the first trimester. All dizygotic twins are dichorionic, diamniotic. Monozygotic twins, on the other hand, may have a variety of presentations depending on the day the zygote divides.2
Sonography cannot distinguish between dizygotic and monozygotic twins unless they are different genders. There are sonographic clues to aid in the identification of chorionicity and amniocity.
First trimester sonographic findings are:
Dichorionic—sacs will be divided by a thick echogenic rim, counting the sacs determines the chorionicity.
Monochorionic—will appear similar to a single gestation with a thick echogenic gestational sac surrounding both fetuses.
Diamniotic—each sac will have its own yolk sac (> 8 weeks). The amniotic sac is very thin and can be difficult to identify in the first trimester.2
Second trimester—Dichorionic findings:
1) Different gender
2) Two separate placentas
3) Twin peak sign—triangular projection of chorion into dividing membrane appears as a “peak” on ultrasound; strong predictor <28 weeks
4) Thickness of membrane—thick membrane, more than 1 mm, is suggestive of dichorionicity. This finding is more accurate less than 26 weeks but is still a weak predictor.
Twin pregnancies carry a four to six times higher perinatal mortality, and a two times higher morbidity rate for a variety of reasons. The most common complication of twins is preterm labor. Other complications are growth restriction, anomalies (two to three times more than a singleton), and such maternal conditions as hypertension and preeclampsia.3, 4
Twin-to-Twin Transfusion Syndrome (TTTS). This condition can occur with monochorionic twins. Arteriovenous communications within the placenta can result in TTTS. One fetus will have blood shunted away and is labeled the donor, while the other fetus will receive the shunted blood and is labeled the recipient. This syndrome presents with a series of sonographic findings related to the shunting of blood. The donor twin is commonly growth restricted with a discordance between the twins of more than 20%. There is often oligohydramnios with the donor and polyhydramnios with the recipient. The donor fetus will appear “stuck” in the sac. This appearance is characteristic of TTTS. The donor will become hypovolemic and anemic. Umbilical cord Doppler images often show an increased systolic/diastolic ratio, demonstrating the increased resistance in the umbilical cord. The recipient will become larger, hypervolemic, and plethoric. Hydrops may occur as the fetus enters into congestive heart failure. The ventricular walls of the heart may thicken, and the contractility of the heart may be decreased as the heart failure becomes worse. As the blood flow increases to the recipient, the S/D ratio decreases, and the overall blood velocity is high. Both fetuses are at a significantly increased risk for intrauterine and perinatal mortality.1, 20
Monoamniotic Twins. This entity carries a 50% mortality risk because of cord entanglement that obstructs blood flow to the fetus. Sonographically, color Doppler may be helpful to look for a mass of cord with areas of increased velocity, suggesting stenotic flow.
Conjoined Twins. This is rare. Most conjoined twins are born prematurely, and 40% are stillborn. The most common presentation is fusion of the anterior wall. They may share organs, and those organs can often have abnormalities. Polyhydramnios is present 50% of the time. The most common types are: thoraco-omphalopagus (conjoined chest and abdomen), thoracopagus (conjoined chest), and omphalopagus (conjoined abdomen). They account for 56% of the types of conjoined twins.1, 20
AcardiaC Twin. This is rare. All cases have an arterial-to-arterial shunt and a venous-to-venous shunt allowing for perfusion of the acardiac twin. The acardiac twin either has a rudimentary heart or is completely acardiac. It has a poorly underdeveloped upper body with a small or absent cranium and brain. If it does develop, there are often significant abnormalities. The lungs and abdominal organs may also be abnormal or absent. The lower extremities are slightly more developed.1 The normal, or pump twin is at a great risk for congestive heart failure, which will present on ultrasound as polyhydramnios and fetal hydrops. Chromosomes have been reported to be abnormal in up to 50% of the cases. Doppler can verify the reversed flow in the umbilical cord of the acardiac twin.20
CHROMOSOMAL ABNORMALITIES AND TESTING
Trisomy 21. This is the most common chromosome disorder. Trisomy 21 occurs when there are three copies of chromosome 21. The Down’s syndrome frequency increases with advanced maternal age. At this time, the only definitive test to determine Down’s syndrome is amniocentesis. Noninvasive testing includes blood tests and ultrasound.1
First-trimester screening combines biochemistry markers, maternal age (MA), and fetal nuchal translucency. Nuchal translucency is a measurement made at the back of the fetal neck on the CRL image. It is applicable from 11 to 14 weeks. The nuchal translucency increases with gestational age and normal tables are available for comparison; however, any measurement less than 3 mm is normal. Screening for Down’s syndrome by maternal age and nuchal translucency has been shown to identify 80% of fetuses with Down’s syndrome (with a 5% false-positive rate). Other chromosomal defects (trisomy 18, 13, triploidy, and Turner’s syndrome), cardiac defects, skeletal dysplasias, and genetic syndromes can also present with increased nuchal translucency.3, 19, 20
For the nuchal translucency to be accurate, very strict rules should be followed. The fetus is measured in the sagittal plane, the same used for the CRL. Careful consideration should be taken to bisect the fetus exactly in the midline, evidenced by the umbilical cord insertion. The image should be magnified so that the fetus occupies at least three-fourths of the image. The imager should be able to distinguish between the fetal skin and the amnion, both appearing as a thin membrane. This is accomplished by waiting for the fetus to spontaneously move away from the amnion. The first caliper should be placed so that the horizontal bar of the caliper is on the outside edge of the inner membrane in the nuchal region. The second caliper should be placed so that the horizontal bar is on the inside edge of the fetal skin. The placement of the caliper is very important for the predictability and accuracy of the nuchal translucency. Great care should be taken to achieve the correct image and caliper placement (Fig. 7–47).3, 19, 20
FIGURE 7–47. Fetus with electronic callipers measuring the nuchal translucency.
First-trimester biochemistry includes the analysis of hCG and PAPP-A (pregnancy associated plasma protein A).6 The higher the hCG and the lower the PAPP-A, the higher the trisomy 21 risk. The detection rate of trisomy 21, combining MA, nuchal translucency, and biochemistry is 90%, with a 5% false-positive rate.20
Second-trimester ultrasound markers can be divided into major and minor findings. Major findings warrant offering invasive testing alone; whereas, minor markers require two or more findings to warrant offering invasive testing. Major sonographic markers include: increased nuchal skinfold (>6 mm), cardiac defect, diaphragmatic hernia, omphalocele, facial cleft, and atresia (esophageal or duodenal).3, 20 Minor markers include abnormal ratio of observed/expected femur and humeral lengths, hypoplasia of midphalanx of fifth digit, echogenic foci of the heart, pyelectasis, echogenic bowel, sandal gap toe, choroid plexus cysts, small ears and, most recently, nasal bone.6, 20
Second-trimester biochemistry or maternal serum AFP3 (MSAFP3), consists of hCG, AFP, and estriol. A risk of trisomy 21 is calculated based on these values. The risk increases with a higher hCG, lower AFP, and lower estriol. Combining the ultrasound with the biochemistry markers will detect approximately 60% of trisomy 21 fetuses.20
Trisomy 18. In this disorder, there are three copies of chromosome 18. Ninety-five percent are an intrauterine demise or stillborn.1 It is commonly, but not always, associated with multiple defects. Sonographically, these major findings may be seen with trisomy 18; growth restriction, increased nuchal translucency, neural tube defect, strawberry-shaped head, choroid plexus cysts, ACC, enlarged cisterna magnum, decreased extremity lengths, cardiac defects, diaphragmatic hernia, esophageal atresia, omphalocele, and renal agenesis. Minor ultrasound findings include clenched hands, echogenic bowel, rocker-bottom feet, micrognathia, and single umbilical artery.6, 20 MSAFP3 shows all three markers decreased.1
Trisomy 13. In this disorder, there is an extra copy of chromosome 13. It may be associated with multiple abnormalities; however, the most common sonographic findings are holoprosencephaly (including the facial spectrums), cardiac defects, postaxial polydactyly, echogenic or polycystic kidneys, omphalocele, and microcephaly.1, 20
Triploidy. In this disorder, there are three complete sets of chromosomes. If paternally derived, the typical finding is a large placenta with multiple cystic areas (partial mole). If maternally derived, multiple findings include severe IUGR with an abnormally large head and small abdomen, hypertelorism, micrognathia, ventriculomegaly, cardiac defects, neural tube defect, holoprosencephaly, Dandy-Walker malformation, cystic hygroma, renal anomalies, clubbed feet, single umbilical artery, and oligohydramnios.1, 20
Sex Chromosome Abnormalities. The main sex chromosome abnormalities are Turner’s syndrome, 47, XXX; 47, XXY; and 47, XYY.20 Sonographically, Turner’s syndrome findings are cystic hygroma, lymphangiectasia, cardiac defects, renal abnormalities, and hydrops.1, 20 The other sex chromosome abnormalities do not typically have prenatal sonographic findings.
Amniocentesis. This is an invasive procedure in which a needle is inserted into the amniotic cavity and amniotic fluid is withdrawn. The amniotic fluid is typically assessed for karyotype, levels of amniotic fluid bilirubin associated with Rh disease, amniotic fluid alpha-fetoprotein, acetylcholinesterase for spinal defects, infection, fetal lung maturity, and specific DNA studies. Our institution quotes a 1:300 risk of miscarriage with amniocentesis based on the national average. The standard amniocentesis is offered after 14 weeks.
Fluorescence in Situ Hybridization (FISH). This is currently an adjunct to amniocentesis. It is considered experimental at this time, so all findings from this test must be confirmed by amniocentesis results. “Tags,” or markers, that attach to certain chromosomes (currently testing 13, 18, 21, × and Y) fluorescence. This allows the geneticist to count the chromosomes for extra or deleted chromosomes. Results are available in 24–48 hours.21
Early amniocentesis is performed the same as amniocentesis but during the 11th to 14th weeks of gestation. It has been associated with many problems. The loss rate is higher, 1:100, and is technically more difficult to perform because of the lack of fusion of the amnion and chorion. The unfused membranes are difficult to penetrate and often cause the need for multiple sticks, which in turn, increases the loss risk. Early amniocentesis has also been associated with talipes equinovarus.20
Chorionic Villus Sampling (CVS). This is a procedure in which a catheter is inserted into the placenta and chorionic villi are aspirated for karyotyping. This procedure may be done transabdominally or transvaginally, depending on placental location. CVS is performed between 10 and 12 weeks and results are obtained in 3–8 days versus 10–14 days for amniocentesis. CVS does not test for amniotic fluid alpha-fetoprotein and cannot rule out spinal defects. Although the loss rate is 1:100. Although the loss rate is slightly higher than amniocentesis, the CVS loss rate is comparable to early amniocentesis. CVS performed <10 weeks has an association with severe limb defects and is not typically performed at that time.2, 20, 21
Percutaneous Umbilical Blood Sampling (PUBS). This is similar to an amniocentesis except that the needle is advanced through the amniotic fluid to the cord insertion site into the placenta. The needle is then inserted into the base of the umbilical cord. CDS can aid in locating the umbilical cord insertion into the placenta.5 This procedure has a higher loss rate, 1–2%, and is technically more difficult to perform. It allows for rapid karyotyping (48–72 hours). PUBS most common application is with Rh isoimmunization testing. The fetal blood is tested for the amount of bilirubin pigment and allows the perinatologist to perform a blood transfusion if necessary.21
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16. Bianchi DW, Crombleholme TM, et al. Fetology Diagnosis and Management of Fetal Patient. New York: McGraw-Hill; 2000.
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18. Tortora GJ, Derrickson B. Principles of Anatomy and Physiology. 11th ed. Hoboken, NJ: John Wiley & Sons. Inc; 2006.
19. Hagen-Ansert SL. Textbook of Diagnostic Ultrasonography. 7th ed. St. Louis, MO: Mosby; 2012.
20. Creasy RK, Resnik, R. Maternal-Fetal Medicine. 6th ed. Philadelphia, PA: WB Saunders Company; 2009.
21. Bianchi DW, Crombleholme TM, D’Alton ME. Fetalogy: Diagnosis and Management of the Fetal Patient. New York: McGraw-Hill; 2000.