MRI of Fetal and Maternal Diseases in Pregnancy 1st ed.

18. Magnetic Resonance Imaging of Acute Abdominal and Pelvic Pain in Pregnancy

Shaun R. Best1Lorene E. Romine1 and Michele A. Brown 


Department of Radiology, University of California, San Diego, CA, USA

Michele A. Brown



Magnetic resonance imagingPregnancyAbdominal painPelvic pain

18.1 Introduction

Acute abdominal and pelvic pain during pregnancy presents a diagnostic challenge. Non-obstetric causes of abdominal and pelvic pain in the pregnant patient are similar to that of the nonpregnant patient, leading to a vast differential diagnosis including gastrointestinal, biliary, genitourinary, and gynecologic etiologies [1]. Clinical evaluation is limited by the gravid uterus. Also, several altered laboratory parameters are considered normal during pregnancy, such as mild leukocytosis, anemia, and elevated alkaline phosphatase. Nausea, vomiting, and abdominal pain are also common symptoms occurring in the pregnant woman without significant abdominal and pelvic pathology. Thus, it may be difficult for the clinician to rely upon clinical presentation and laboratory findings alone to elucidate an accurate diagnosis. Imaging plays a very important role in the accurate diagnosis and management of the pregnant patient presenting with acute abdominal or pelvic pain. While detailed discussions of specific organ systems will be accomplished in subsequent chapters, the current chapter aims to provide a general overview.

Ultrasound is routinely utilized in the workup of abdominal pain during pregnancy as it is widely available, inexpensive, and safe. Ultrasound, however, is operator dependent and limited in the setting of displaced anatomic structures and overlying bowel gas. Given the radiation exposure doctrine of “as low as reasonably achievable,” traditional radiography and computed tomography play a small role in the workup of abdominal and pelvic pain in the nontraumatic setting given their inherent use of ionizing radiation. MRI provides exquisite anatomic detail and tissue contrast without ionizing radiation. The vast majority of cases do not require intravenous contrast material and may be done with relatively few MRI sequences. If the clinical question cannot be answered accurately by ultrasound and MRI is readily available, MRI is a sensible next step to aid diagnosis, and delayed diagnosis is the single greatest factor in morbidity and mortality of the pregnant patient presenting with acute abdominal disease [2].

Specific patient preparation is not routinely required; however, some investigators propose that the patient should fast for at least 4 h prior to the examination to reduce bowel peristalsis and fetal motion [3]. The majority of patients can be imaged in the supine position, specifically during the first trimester; however, during the third trimester, a left lateral decubitus position is preferable due to patient comfort and to decrease pressure on the inferior vena cava by the gravid uterus. For patients in whom there is clinical concern of left hydronephrosis and hydroureter, a right lateral decubitus position can be employed to alleviate pressure on the left-sided abdominal structures by the gravid uterus [2]. A phased array coil is typically used throughout the examination with a body coil reserved for larger patients if multiple phased array coils are not available.

Ideally the examination is monitored by the radiologist and sequences chosen to answer the clinical question in the least amount of time possible. A typical MRI examination for evaluation of abdominal and pelvic pain in the pregnant patient consists of axial T1-weighted dual-echo gradient-recalled echo (GRE), and axial, coronal, and sagittal T2-weighted single-shot fast spin echo (e.g., SSFSE or HASTE) images, as well as axial and coronal T2-/T1-weighted fast imaging with steady-state free precession (e.g., FISP or FIESTA) images (Fig. 18.1a–d). Additional sequences that may be beneficial include fat-suppressed T2-weighted or short tau inversion recovery (to evaluate for inflammation), fat-suppressed T1-weighted GRE (to evaluate for fat versus blood products), additional SSFSE/HASTE images utilizing oblique imaging planes or thinner slices to evaluate smaller structures, or diffusion-weighted imaging (Fig. 18.2a–e). If MR cholangiopancreatography or MR urography is indicated, additional thin-slice 3D heavily T2-weighted echo train spin echo sequences can be performed (Fig. 18.2f). If feasible, images should be reviewed by the radiologist and additional sequences performed as necessary. Currently, gadolinium-based intravenous contrast agents are considered pregnancy category C by the FDA and are rarely used in the setting of acute abdominal or pelvic pain to make an accurate diagnosis in pregnant patients.


Fig. 18.1

Routine non-contrast MR sequences in the evaluation of abdominal and pelvic pain in the pregnant patient. Example of axial T2-weighted single-shot echo train spin echo image (a) demonstrates a uterine fibroid with mildly increased T2-weighted signal and surrounding fluid suggestive of degeneration (arrow). Example of T2-/T1-weighted steady-state free precession image in a different patient (b). T1-weighted dual-echo gradient-recalled echo images in-phase (c) and opposed phase (d) in a third patient demonstrate a large dermoid (straight arrows) with evidence of internal fat (curved arrow). The lesion did not show evidence of torsion by imaging


Fig. 18.2

Optional non-contrast MR sequences. Examples of axial T2-weighted image with fat suppression showing normal ovaries (a), T1-weighted GRE image with fat suppression in a patient with endometriosis (b), T2-weighted image with oblique angle in a patient with uterine anomaly (c), T2-weighted image with high resolution in a patient with cervical carcinoma diagnosed during pregnancy (d), diffusion-weighted image in a patient with uterine duplication and obstructing vaginal septum (e), and thin-slice 3D heavily T2-weighted image from MR urography in a patient with physiologic hydronephrosis of pregnancy (f)

During the first trimester, extrauterine pelvic anatomy is not yet significantly altered and resembles that of the nonpregnant female. The uterus maintains its version and flexion, typically anterior and best demonstrated on sagittal images. The bladder lies anterior and inferior to the uterus, and the vagina is posterior to the bladder and urethra. The rectum and anus lie posterior to the vagina. Typical location of the ovaries is lateral to the midline uterus, and ovaries are typically easily recognized secondary to high signal intensity of the ovarian follicles on T2-weighted imaging. During the second and third trimesters, the uterus becomes an intra-abdominal organ due to increase in size and displaces many pelvic contents from their normal location. The appendix is often displaced superiorly as are the adnexal structures.

18.2 Causes of Acute Abdominal and Pelvic Pain in Pregnancy

18.2.1 Gastrointestinal Acute Appendicitis

Acute appendicitis is the most common non-obstetric surgical condition in pregnancy [45]. Early and accurate diagnosis is of paramount importance because of increased fetal loss rate of 30 % seen with appendiceal rupture compared to <2 % fetal loss rate in the absence of rupture [6]. The clinical diagnosis of appendicitis can be difficult due to atypical location of pain secondary to cephalad migration of the cecum and appendix by the gravid uterus [2], as well as physiologic leukocytosis observed during pregnancy. MRI can be useful to exclude appendicitis if a normal appendix is visualized (Fig. 18.3). MRI has been shown to be superior in the visualization of the normal appendix compared to ultrasound [7], and the appendix can be visualized with high accuracy in the pregnant patient, estimated at 83–91 % [810]. In the acute setting, MRI shows good diagnostic accuracy of appendicitis with sensitivity of 80–100 % and specificity of 93.6–100 % [79].


Fig. 18.3

Normal appendix. Axial T1-weighted (a), axial T2-weighted with fat saturation (b), and coronal T2-weighted (c) MR images demonstrate a nondilated appendix with no adjacent inflammation (curved arrows)

The MR imaging findings of acute appendicitis are similar to that of the nonpregnant patient. T2-weighted imaging demonstrates a dilated appendix and mural thickening (Fig. 18.4). Periappendiceal fluid can be seen as high signal intensity on T2-weighted images and may be more readily visualized utilizing fat suppression techniques. Periappendiceal abscess can be seen in the setting of a ruptured appendix (Fig. 18.5). Contrast is rarely needed for diagnosis; however, if contrast is administered, the appendix would demonstrate mural enhancement.


Fig. 18.4

Acute uncomplicated appendicitis. Axial T2 weighted (a) and T2 weighted with fat saturation (b) MR images demonstrate a dilated, thick-walled appendix with adjacent fat stranding and inflammation (curved arrows). Coronal T2-weighted image in a different patient (c) reveals similar findings of a dilated fluid-filled appendix with mild periappendiceal inflammation (arrow)


Fig. 18.5

Appendicitis with rupture and abscess. Axial T1-weighted (ab) and T2-weighted (cd) images show a heterogeneous mass in the right lower quadrant with adjacent inflammation compatible with perforated appendicitis and surrounding mass (arrowsac). Notice the small hypointense structure in the center of the inflammation (arrowsbd) consistent with a small appendicolith Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) has a peak age distribution similar to that of childbearing age in the female, with peak incidence at 15–25 years [11]. IBD is a common mimicker of appendicitis in that the terminal ileum is involved in approximately 80 % of patients with IBD [1112]. Patients will typically present with diffuse abdominal pain, diarrhea, nausea, and vomiting. The colon can be involved with associated involvement of the small intestine in approximately 50 % of cases and in isolation in about 15–20 % of cases [11]. MR is accurate in the evaluation of IBD and its complications including abscess, fistula, and strictures [1112].

Typical imaging features include concentric wall thickening, bowel wall, and mesenteric edema presenting as high T2 signal intensity in the acute phase [1314]. There may be associated mesenteric lymphadenopathy or fibrofatty proliferation, as well as reactive free fluid [1314]. Bowel Obstruction

The majority of bowel obstructions during pregnancy are secondary to adhesions, estimated at up to 58 % [15]. Additional causes include volvulus, intussusception, and inflammatory bowel disease. Imaging features consist of dilated fluid-filled bowel loops of small and/or large bowel. Small bowel is considered dilated when measured greater than 2.5 cm in diameter [16] and large bowel when measured greater than 6 cm or greater than 9 cm at the cecum [17]. Bowel obstruction is best depicted utilizing HASTE/SSFSE or FISP/FIESTA images (Fig. 18.6).


Fig. 18.6

Small bowel obstruction. Coronal T2-weighted images (ab) reveal dilated loops of small bowel within the right lower quadrant of the abdomen (curved arrowa) with decompression to more normal caliber small bowel in the right lower quadrant (curved arrowb) Abdominal Wall Hernia

The presence of an enlarged, gravid uterus and displacement of intra-abdominal structures can cause small bowel or omentum to protrude through an existing or acquired ventral or umbilical hernia. This can lead to bowel obstruction or omental ischemia and pain from incarceration (Fig. 18.7). Signs suggestive of incarceration include fluid within the hernia sac, wall thickening of herniated bowel loops, and dilatation of bowel proximal to the hernia [18].


Fig. 18.7

Incarcerated umbilical hernia. Axial T1-weighted (a) and T2-weighted with fat saturation images show a small fat-containing umbilical hernia with surrounding inflammation (arrowab)

18.2.2 Hepatobiliary Acute Cholecystitis

Acute cholecystitis is the second most common condition necessitating surgery during pregnancy [12]. Ninety percent of cases of acute cholecystitis during pregnancy are secondary to gallstones [15]. Pregnancy is a known risk factor for cholelithiasis as the pregnant state leads to increased cholesterol synthesis by estrogen and decreased gallbladder motility by progesterone [19]. Ultrasound is the primary method for diagnosis, but MR boasts relatively high sensitivity of 88 % and specificity of 89 % [15]. Imaging findings include gallbladder wall thickening and edema with pericholecystic fluid, best demonstrated as high signal intensity on T2-weighted images. While these findings are readily diagnosed on ultrasound, it can be very difficult to image choledocolithiasis with ultrasound alone. MRCP can detect stones within the biliary tree with a sensitivity of 89–100 % and specificity of 83–100 % [20]. Choledocolithiasis is depicted as a low signal intensity filling defect on T2-weighted/MRCP images with upstream dilatation above the site of the filling defect [20] (Fig. 18.8). One must be careful not to mistake flow artifact, which is seen as an intermediate signal intensity, centrally located filling defect on a single sequence, for a choledocolith [21]. MRCP can also limit the performance of unnecessary ERCP when no stones are visualized in the biliary system.


Fig. 18.8

Choledocolithiasis. Heavily T2-weighted coronal MRCP images demonstrate numerous hypointense gallstones in the gallbladder (arrowheada) and several small filling defects within the dilated cystic duct compatible with small stones (arrowa). Additional MRCP image reveals numerous fillings defects within the dilated extrahepatic common duct compatible with choledocolithiasis (arrowb) Acute Pancreatitis

The majority of cases of pancreatitis during pregnancy are secondary to gallstones [12]. The presentation is similar to that of the nonpregnant female with abdominal pain, nausea, and vomiting. Diagnosis remains a clinical one and serum amylase/lipase are reliable serum markers during pregnancy. MR can be utilized to stage the severity of acute pancreatitis and to evaluate for complications [22] with accurate depiction of peripancreatic inflammation and/or fluid collections on T2-weighted images.

18.2.3 Renal Hydronephrosis

Hydronephrosis is very common during pregnancy secondary to smooth muscle relaxation in the ureters from hormonal changes and from extrinsic compression of the ureters by the pelvic brim [4]. Physiologic hydronephrosis of pregnancy is typically asymptomatic and requires no intervention. Physiologic hydronephrosis will be depicted on T2-weighted images as tapered narrowing of the ureter at the sacral promontory with a collapsed pelvic ureter (Fig. 18.9). Ultrasound is typically the diagnostic test of choice for the evaluation of hydronephrosis; however, depiction of the distal ureters is difficult. In the setting of flank pain, an obstructing calculus should be excluded, and MR is a reasonable next step in the pregnant patient. Positioning the patient in the decubitus position with symptomatic side up may help identify an obstructing distal ureteral calculus by alleviating uterine pressure on the pelvic brim, which could mask a calculus [2]. A ureteral calculus will present as a hypointense convex filling defect with upstream dilatation of the ureter [23].


Fig. 18.9

Hydronephrosis of pregnancy. Heavily weighted T2-weighted coronal MR urography image reveals bilateral hydroureteronephrosis to the level of the pelvic brim (curved arrows) with no discrete filling defects to suggest obstructing calculus. Notice the pelvic ureters are not dilated, suggesting no obstruction from a distal stone. Findings are compatible with hydronephrosis of pregnancy Pyelonephritis

Pyelonephritis is more common in the pregnant patient than the nonpregnant patient secondary to urinary stasis [2]. Presenting symptoms are similar to the nonpregnant patient with fever, flank pain, and nausea as common symptoms. Diagnosis is primarily clinical and treatment empirical with imaging reserved for recurrent pyelonephritis or to detect or exclude complications such as perinephric abscess. MR features include enlargement of the kidney with adjacent perinephric fluid and stranding [24] (Fig. 18.10). Areas of increased or heterogeneous signal intensity of the cortex may be seen secondary to edema.


Fig. 18.10

Pyelonephritis. Coronal T2-weighted image in a patient with right-sided pain demonstrates right perinephric stranding and fluid (curved arrow)

18.2.4 Gynecologic/Obstetric Uterine

Uterine leiomyomas (fibroids) can grow rapidly during pregnancy resulting in mass effect, degeneration, or torsion [2526]. Either of these can result in significant patient pain. MR is useful in the characterization of leiomyomas during pregnancy [27]. An uncomplicated leiomyoma appears the same on MR as the nonpregnant patient, characterized as a well-demarcated mass encased by uterine serosa. An exophytic fibroid may demonstrate a bridging vessel from the uterus to the mass. The majority will demonstrate low signal intensity on T2-weighted imaging and low-to-intermediate signal intensity on T1-weighted imaging [28]. In the setting of acute degeneration, the leiomyoma will demonstrate central high signal intensity on T2-weighted imaging [28] (Fig. 18.11). Pregnant patients are prone to developing red degeneration of leiomyomas due to hemorrhagic infarction, which displays a characteristic red appearance (hemorrhagic) at gross pathology [28]. This occurs secondary to venous thrombosis within the tumor or rupture of intramural arteries [28]. Typical MR findings include peripheral or diffuse T1-weighted high signal intensity and variable T2-weighted signal intensity. Pedunculated subserosal leiomyomas may also be prone to torsion as the uterus and fibroid rapidly increase in size in the setting of pregnancy. A torsed leiomyoma will appear as a pedunculated or subserosal mass with variable T1-weighted signal and central high T2-weighted signal intensity (Fig. 18.12). While torsion is rare, MR is also useful in differentiating a benign leiomyoma from a suspected adnexal mass when ultrasound is equivocal.


Fig. 18.11

Degenerated uterine fibroid. Sagittal T2-weighted (a) and T1-weighted (b) images show a heterogeneous intramural myometrial mass in the lower uterine segment (arrowsab). Foci of increased T2 signal are present within the mass consistent with degeneration


Fig. 18.12

Torsed uterine fibroid. Axial T2-weighted image demonstrates a pedunculated subserosal fibroid (arrows) with foci of increased internal signal intensity consistent with degeneration. There is also a small amount of adjacent fluid and inflammation in the right lower quadrant. Surgical exploration revealed torsion of this pedunculated subserosal fibroid Adnexal Torsion

The majority of adnexal masses that are discovered during pregnancy are asymptomatic and are comprised of benign ovarian cysts such as corpus luteal, follicular, hemorrhagic, and endometriotic [12]. Ovarian torsion occurs more often in the pregnant patient and can occur in the setting of a normal ovary or with an associated adnexal mass. Symptoms may mimic appendicitis including pelvic pain, nausea, and vomiting. The ovary twists on its vascular pedicle constricting blood supply to the ovary. This leads to an enlarged and edematous ovary, which can be visualized by MR with associated increased signal intensity of the ovarian stroma on T2-weighted imaging (Fig. 18.13). T1-weighted signal intensity will vary depending on the presence or absence of associated blood products.


Fig. 18.13

Ovarian torsion. Axial T2-weighted images show an enlarged and edematous right ovary (arrowa) compared to normal-appearing left ovary (arrowb) consistent with right ovarian torsion Ectopic Pregnancy

Ectopic pregnancy is the leading cause of maternal mortality during the first trimester occurring in an estimated 1–2 % of all pregnancies [2930]. Ultrasound is the initial imaging modality of choice, but on occasion, ectopic pregnancy cannot be definitively excluded by ultrasound alone. MR imaging can be useful in these situations allowing for higher tissue contrast resolution and additional anatomic localization and may demonstrate an unsuspected ectopic or the rare heterotopic pregnancy. Approximately 98 % of ectopic pregnancies occur in the fallopian tubes, particularly the ampullary portion [30]. MR features of a tubal ectopic are an adnexal cystic structure with a thickened wall or adnexal mass with associated isointense to low signal intensity on T1-weighted imaging and high signal intensity on T2-weighted imaging [30] (Fig. 18.14). High T1 signal and low T2 signal areas may be seen in the setting of hemorrhage. Diffusion-weighted imaging may demonstrate a ring or dot-like area of high signal intensity. There may be associated hemoperitoneum or hematosalpinx, which will be present as high signal intensity on T1-weighted images [30].


Fig. 18.14

Ectopic pregnancy. Axial T2-weighted (a) and T1-weighted (b) images demonstrate a heterogeneous, thick-walled mass in the right lower quadrant adjacent to the uterus (arrowsab). No evidence of hemorrhage is seen in this case although hemorrhage may be seen in ovarian torsion. No intrauterine gestational sac was visualized. A separate normal right ovary was seen (not pictured). Findings are compatible with right tubal ectopic pregnancy



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