These, gentlemen, are the tuberosities of the ischia, on which man was designed to sit and survey the works of creation.
Oliver Wendell Holmes (1809-1894), Life and Letters of Oliver Wendell Holmes, Vol. I, Chapter VII
FIG. 8.1 Sagittal, T1-weighted contrast-enhanced MRI of the pelvis demonstrating endometrial carcinoma of the uterus.
The pelvis provides structural support for the body and encloses the male and female reproductive organs. Because of its role as a support mechanism for the body, the pelvis has a large amount of musculoskeletal anatomy, which, together with the differences in male and female reproductive anatomy, makes this area challenging to learn (Fig. 8.1).
OBJECTIVES
• Identify the structures of the bony pelvis.
• Define the pelvic inlet and outlet.
• Describe the perineum.
• Describe the function and location of the pelvic muscles.
• Differentiate between the pelvic diaphragm and perineum.
• Describe the location of the bladder in relation to the reproductive organs and the course of the male and female urethras.
• Describe the location and function of the male and female reproductive organs.
• Identify the major arteries and veins that are located within the pelvis.
• Describe the location of the pelvic lymph nodes.
• List and describe the components of the rectum.
BONY PELVIS
Sacrum, Coccyx, and Hip Bones (Innominate Bones)
The bony pelvis is formed by the sacrum, coccyx, and two hip bones or innominate bones (Figs. 8.2 and 8.3). The sacrum is a triangular-shaped bone formed by the fusion of five vertebral segments. The first sacral segment has a prominent ridge located on the anterior surface of the body termed the sacral promontory, which acts as a bony landmark separating the abdominal cavity from the pelvic cavity (Figs. 8.3 and 8.5). The transverse processes of the five sacral segments combine to form the lateral mass (ala), which articulates with the hip bones at the sacroiliac joints (Figs. 8.3-8.5). The lateral mass contains sacral foramina that allow for the passage of sacral nerves (Figs. 8.2, 8.6, and 8.7). Articulating with the fifth sacral segment is the coccyx, which consists of three to five small fused bony segments (Figs. 8.2, 8.3, and 8.8).
The hip bones are made up of three bones: the ilium, pubis, and ischium (Fig. 8.9).
Ilium. The ilium, the largest and most superior portion, consists of a body and a large winglike projection called the ala (Figs. 8.9-8.11). The concave, anterior surface of the ala is termed the iliac fossa, which is separated from the body by the arcuate line. This arch-shaped line, which is located on the anterior surface of the ilium, forms part of the pelvic brim (Figs. 8.11 and 8.12). The superior ridge of the ala is termed the iliac crest; it slopes down to give rise to the superior and inferior iliac spines on both the anterior and posterior surfaces (Figs. 8.98.11). The body of the ilium creates the upper portion of the acetabulum, which is a deep fossa that articulates with the head of the femur (Figs. 8.13 and 8.14).
Pubis. The pubis, or pubic bone, forms the lower anterior portion of the acetabulum and consists of a body and superior and inferior pubic rami (Fig. 8.9). The bodies of the two pubic bones meet at the midline to form the pubic symphysis (Figs. 8.2, 8.12, and 8.15). The superior pubic ramus projects inferiorly and medially from the acetabulum to the midline of the body (Figs. 8.2, 8.3, and 8.16). Located on the upper surface of the superior pubic ramus is a ridge termed the pectineal line, which is continuous with the arcuate line of the ilium, forming the pelvic brim (Fig. 8.12). Also on the superior surface is the pubic tubercle, which is the attachment site for the inguinal ligament (Figs. 8.2 and 8.3). The inferior pubic ramus projects inferiorly and laterally from the body to join the ischium at an indistinct point; therefore the two together are often referred to as the ischiopubic ramus (Figs. 8.11 and 8.17).
Ischium. The ischium is the inferior portion of the hip bones and, like the pubis, is composed of a body and two rami. The body of the ischium forms the lower posterior portion of the acetabulum (Figs. 8.9, 8.11, 8.13, and 8.14). The superior ischial ramus extends posteriorly and inferiorly to a roughened, enlarged area termed the ischial tuberosity (Figs. 8.9, 8.10, and 8.17). From the ischial tuberosity, the inferior ischial ramus extends anteriorly and medially to join the inferior pubic ramus.
The ischial spine projects from the superior ischial ramus between two prominent notches on the posterior surface of the hip bones (Figs. 8.9-8.11 and 8.16). The greater sciatic notch extends from the posterior inferior iliac spine to the ischial spine, and the lesser sciatic notch extends from the ischial spine to the ischial tuberosity (Figs. 8.9 and 8.10). The two notches are spanned by ligaments that create foramina for the passage of nerves and vessels. The union of the pubic rami and ischium creates a large aperture termed the obturator foramen, which is enclosed by the obturator muscles (Figs. 8.3, 8.9, and 8.11).
Pelvic Inlet and Outlet
The pelvis is divided into the false or greater pelvis and the true or lesser pelvis by an oblique plane that extends from the upper anterior margin of the sacrum, along the arcuate line, to the upper margin of the pubic symphysis. The boundary line of this plane is called the pelvic brim, which delineates the boundaries of the abdominal and pelvic cavities (Figs. 8.18 and 8.19). The region above the brim is called the false pelvis, and the region below the brim is called the true pelvis. The superior aperture
or inlet of the true pelvis is measured in the anteroposterior direction from the sacral promontory to the superior margin or crest of the pubic bone. The pelvic outlet or inferior aperture is an opening bounded by the inferior edges of the pelvis and is measured from the tip of the coccyx to the inferior margin of the pubic symphysis in the anteroposterior direction and between the ischial spines in the horizontal direction (Figs. 8.18-8.20).
MUSCLES
Multiple muscles are visualized in the pelvis. For ease of description, the major pelvic muscles have been divided into functional groups: extrapelvic, pelvic wall, and pelvic diaphragm (pelvic floor).
Extrapelvic Muscles
Several of the muscles visualized in the pelvis are actually abdominal muscles, such as the rectus abdominis, psoas, and internal and external oblique muscles. The rectus abdominis muscles, visualized on the anterior surface of the abdomen and pelvis, originate from the pubic symphysis and extend to the xiphoid process and the costal cartilage of the fifth, sixth, and seventh ribs. They function to flex the lumbar vertebrae and support the abdomen. The psoas muscles extend along the lateral surfaces of the lumbar vertebrae and act to flex the thigh or trunk. The external and internal oblique muscles are located on the outer lateral portion of the abdomen and span primarily between the cartilages of the lower ribs to the level of the iliac crest. The oblique muscles work together to flex and rotate the vertebral column and compress the abdominal viscera. An inferior band of fibrous connective tissue from the external oblique muscle folds back on itself to form the inguinal ligament, which extends between the anterior superior iliac spine and the pubic bone (Figs. 8.22, 8.25 and 8.26). Just superior to the inguinal ligament is the inguinal canal, a short (3-6 cm), diagonal tunnel passing through the lower anterior pelvic wall. It has openings at the outer portion called the superficial inguinal ring and the inner portion called the deep inguinal ring. The inguinal canal transmits the spermatic cord in males and the round ligament in females (also see Figs. 7.181-7.187 in Chapter 7).
Many of the muscles visualized in the pelvis are considered to be muscles of the hip. The largest of this group are the gluteus muscles (maximus, medius, minimus), which function together to abduct, rotate, and extend the thigh. The largest and most superficial is the gluteus maximus muscle, which makes up the bulk of the buttocks. The gluteus medius and minimus muscles are smaller in size, respectively, and are deep to the gluteus maximus muscle (Figs. 8.21-8.24; also see Chapter 10).
Indirect inguinal hernias are protrusions of mesenteric fat and the small intestine at the deep inguinal ring into the inguinal canal. These hernias are five times more common than direct inguinal hernias and seven times more common in males. Indirect inguinal hernias are considered to be a congenital defect of the abdominal wall and are frequently present at birth.
Pelvic Wall Muscles
The muscles of the pelvic wall include the piriformis, obturator internus and externus, and iliacus muscles (Figs. 8.21-8.30 and Table 8.1; also see Chapter 10). The piriformis muscle, which acts to rotate the thigh laterally, originates from the ilium and sacrum and passes through the greater sciatic notch to insert on the greater trochanter of the femur (Figs. 8.22, 8.23, and 8.25). The fanshaped obturator internus muscle also functions as a lateral thigh rotator. It extends from the pubic bone and obturator foramen to pass through the lesser sciatic notch and attaches to the greater trochanter of the femur (Figs. 8.24, 8.25, and 8.30). Inserting on the greater trochanter just below the obturator internus muscle is the obturator externus muscle. This strong muscle originates on the obturator foramen, aiding in adduction and rotation of the thigh (Figs. 8.24, 8.30, and 10.29). Extending from the iliac crest and sacrum is the triangular-shaped iliacus muscle (Figs. 8.26-8.28). As the iliacus muscle spans the iliac fossa, it is joined by the psoas muscle to form the iliopsoas muscle, which extends to insert on the lesser trochanter of the femur (Figs. 8.26, 8.29, and 8.30). The iliopsoas muscle is the most important muscle for flexing the leg, which makes walking possible.
TABLE 8.1 Muscles of the Pelvic Wall and Diaphragm
|
Muscle |
Origin |
Insertion |
Function |
|
Piriformis |
Ilium and sacrum |
Greater trochanter of femur |
Laterally rotates and adducts thigh |
|
Obturator internus |
Obturator foramen and pubic bone |
Greater trochanter of femur (medial surface) |
Laterally rotates thigh |
|
Obturator externus |
Obturator foramen |
Greater trochanter of femur (trochanteric fossa) |
Laterally rotates and adducts thigh |
|
Iliacus |
Iliac crest and sacrum |
Lesser trochanter of femur (tendon fused with that of psoas muscle) |
Flexes hip |
|
Levator ani |
Symphysis pubis and ischial spine |
Coccyx |
Supports pelvic viscera, flexes coccyx, elevates and retracts anus |
|
Coccygeus |
Ischial spine |
Sacrum and coccyx |
Assists in supporting the pelvic floor and flexes coccyx |
Pelvic Diaphragm (Pelvic Floor) Muscles
The funnel-shaped pelvic diaphragm, also called the pelvic floor, is a layer of muscles and fascia that forms the greatest majority of the floor of the pelvis. The primary muscles of the pelvic diaphragm are the levator ani and coccygeus muscles. The levator ani muscles are the largest and most important muscles of the pelvic diaphragm, originating from the symphysis pubis and ischial spines to form winglike arches that attach to the coccyx. The levator ani muscles can be subdivided into three parts according to their attachments and the pelvic viscera they are associated with: the pubococcygeus, puborecta- lis, and iliococcygeus muscles. The two coccygeus muscles form the posterior portion of the pelvic diaphragm, arising from the ischial spines and fanning out to attach to the lower sacrum and coccyx. Together, the levator ani and coccygeus muscles provide support for the pelvic contents (Figs. 8.31-8.39 and Table 8.1).
Perineum
The perineum is the area located posterior to the pubic arches and anterior to the coccyx. The bony circumferential boundaries of the perineum are the inner edges of the pelvic outlet and consist of the following surface relationships: anteriorly by the pubic symphysis; laterally by the pubic rami, ischial rami, ischial tuberosities, and sacrotu- berous ligaments; and posteriorly by the coccyx (Fig. 8.40). The region is divided into two triangles, posterior and anterior, by an imaginary line joining the ischial tuberosities. The posterior triangle is the anal triangle, and the anterior triangle is the urogenital triangle. The anal triangle contains the inferior one-third of the anal canal and its sphincter muscles, as well as the ischioanal fossa (Figs. 8.34, 8.35, 8.40, and 8.42). The urogenital triangle contains the openings of the urethra and vagina in the female and the urethra and root structures of the penis in the male (Figs. 8.40-8.42). It is covered by a tough layer of fascia, called the perineal membrane, stretching between the pubic arches. Located at the center of the midpoint between the ischial tuberosities is the perineal body, a mass of muscle and fascia that is the site where the interlacing fibers of several muscles converge. In females, the perineal body is located between the vagina and rectum, and in males, it is located between the rectum and root of the penis (Fig. 8.40).
The perineal body is an important structure in females because of its function as a support for the pelvic organs. When muscles connected to the perineal body stretch or tear (i.e., during childbirth), the muscular support of the pelvic floor can be compromised, resulting in prolapse of the pelvic organs. Injury to the perineal body due to trauma or infection can result in the formation of a fistula.
VISCERA
The pelvic cavity contains the bladder, rectum, and internal reproductive organs.
Bladder
The bladder is a pyramid-shaped muscular organ that rests on the pelvic floor, immediately posterior to the pubic symphysis (Figs. 8.43-8.51). It functions as a temporary reservoir for the storage of urine. In a normal adult, it takes approximately 200 to 250 mL of urine to accumulate before the urge to urinate is triggered. However, the bladder has the potential storage capacity of approximately 750 mL. The superior body of the bladder is covered by peritoneum, allowing loops of ileum and sigmoid colon to rest on it. The posterior aspect is referred to as the fundus or base of the bladder. The base is closely related to the anterior wall of the vagina in the female and to the rectum in the male. Facing toward the pubic symphysis is the apex of the bladder. The inferior portion is a funnel-shaped narrowing called the neck of the bladder, which is continuous with the urethra (Fig. 8.43). The bladder neck contains the muscular internal urethral sphincter, which provides for involuntary control over the release of urine from the bladder. Three openings in the floor of the bladder form a triangular area called the trigone. Two of the openings are created by the ureters (Fig. 8.38). The third opening is located in the apex of the trigone and is formed by the entrance to the urethra (Figs. 8.38, 8.43-8.47, and 8.52). The pelvic portions of the ureters run anterior to the internal iliac arteries and enter the posterolateral surface of the bladder at an oblique angle (Figs. 8.49 and 8.51).
The bladder is anchored to the pelvis by peritoneal ligaments. The apex is attached to the anterior abdominal wall by the median umbilical ligament, which is the remnant of the fetal urachus (obliterated umbilical artery). Two medial umbilical ligaments from the body of the bladder ascend along with the median umbilical ligament to the umbilicus (Fig. 8.48). The fibrous cords of these ligaments represent the obliterated remains of the two umbilical arteries, which provided blood to the placenta during fetal development. The bladder neck is held in place by the puboprostatic ligament in males and the pubovesical ligament in females.
The urethra is a muscular tube that drains urine from the bladder. In both genders, the urethra passes through the perineal membrane, which contains the external urethral sphincter muscle responsible for the voluntary closure of the bladder. The short (3-4 cm) female urethra is located in front of the anterior vaginal wall and descends inferiorly and anteriorly to terminate at the external urethral opening located between the clitoris and vagina (Figs. 8.43, 8.44, and 8.52). The male urethra is much longer (18-20 cm) and extends from the inferior portion of the bladder to the tip of the penis (Figs. 8.45, 8.46, and 8.53). It can be subdivided into three regions: prostatic urethra, membranous urethra, and penile urethra. The prostatic urethra passes through the middle of the prostate gland. The membranous urethra is the shortest and narrowest portion of the urethra and is the portion that penetrates the perineal membrane. The penile urethra is the longest portion, extending from the external urethral sphincter to the tip of the penis (Figs. 8.45 and 8.46). The male urethra has the dual function to drain urine from the bladder and to receive secretions from the prostatic and ejaculatory ducts and the ducts of the bulbourethral glands.
Rectum
The rectum is the terminal part of the large intestine extending from S3 to the tip of the coccyx; it is approximately 15 cm long. It follows the anteroposterior curve of the sacrum and coccyx (sacral flexure) and ends by turning inferiorly and anteriorly (perineal flexure) to become the anal canal, which ends at the anus (Figs. 8.43-8.46 and 8.54-8.57). Between the two flexures is a fold of tissue called the transverse rectal fold (Kohlrausch’s fold) located 5 to 8 cm from the anus (Fig. 8.54). It serves as a topographic landmark during a rectal examination marking the posterior side of the prostate in males and the vault of the vagina in females. The upper third of the rectum, the rectal ampulla, has considerable distensibility. As fecal material collects in this area, it triggers the urge to defecate. The anal canal is the distal portion of the rectum and contains small longitudinal folds called rectal or anal columns. The anus marks the exit of the anal canal and is under the involuntary control of the internal anal sphincter, a circular muscle layer within the rectal wall. The external anal sphincter consists of a ring of skeletal muscle fibers and is under voluntary control (Figs. 8.40, 8.43, 8.45, and 8.54-8.57).
Female Reproductive Organs
The female reproductive system is responsible for producing sex hormones and ova and functions to protect and support a developing embryo. The principal organs of the female reproductive system are located within the pelvic cavity and include the uterus, ovaries, uterine tubes, and vagina (Figs. 8.58-8.60).
Uterus. The uterus is a pear-shaped muscular organ located in the pelvic cavity between the bladder and the rectum (Figs. 8.58 and 8.59). The uterus can be subdivided into two anatomic regions: body and cervix. The body is the largest division, comprising the upper two- thirds of the uterus. The rounded superior portion of the body is called the fundus, which is located just superior to the region where the uterine tubes enter the uterus.
FIG. 8.58 Sagittal view of female pelvis.
The lateral borders of the fundus contain the cornua, where the uterine tubes attach to the uterus. The narrow inferior third of the uterus is called the cervix, which communicates with the vagina. The narrow lumen within the cervix, called the cervical canal, is a conduit between the uterine cavity superiorly via the internal os and opens inferiorly into the vagina via the external os (Fig. 8.60). The most common position of the uterus is with the body projecting superiorly and anteriorly over the bladder, with the fundus adjacent to the anterior abdominal wall and the cervix directed inferiorly and posteriorly into the upper end of the vagina or vaginal vault (Figs. 8.47 and 8.59). The wall of the uterus is composed of three layers: the endometrium is the inner glandular tissue lining the inner wall and responds to cyclic ovarian hormone changes; the myometrium is the middle, muscular layer and the thickest component of the uterine wall; and the perimetrium is the outer layer, consisting of a serous membrane that covers the fundus and posterior surface of the uterus (Figs. 8.59 and 8.60). The endometrium is lined by a mucous membrane that is continuous with the inner lining of the vagina and uterine tubes. The thick myometrial layer is highly vascular and is responsible for the main contractive force during childbirth. The perimetrium is formed by peritoneum and is firmly attached to the myometrium. The uterus is the reproductive organ responsible for protecting the fetus during development (Figs. 8.58-8.63).
Suspensory Ligaments of the Uterus. The uterus is stabilized by several pairs of suspensory ligaments formed by the peritoneum. The round ligaments extend laterally from the uterine cornua, through the inguinal canal, and anchor to the labia majora (Figs. 8.62-8.65). They help keep the uterine body flexed anteriorly (an- teversion) and help prevent posterior movement of the uterus. The uterosacral ligaments extend from the lateral walls of the cervix and course posteriorly around the rectum to anchor to the anterior surface of the sacrum, preventing forward movement of the uterus (Figs. 8.64-8.66). The lateral cervical (cardinal) ligaments are located at the base of the broad ligament and extend like a fan from the lateral walls of the cervix and vagina to anchor into the fascia of the obturator internus muscle and pelvic wall. They help suspend the uterus above the bladder and prevent downward displacement of the uterus (Figs. 8.65, 8.67, and 8.68). Additional support is provided by the muscles and fascia of the pelvic floor.
Ovaries. The paired ovaries are small almond-shaped organs located on either side of the uterus (Figs. 8.60-8.62, 8.64, 8.65, and 8.69-8.73). They lie in a depression on the lateral walls of the pelvis and are held in place by the ovarian and suspensory ligaments (Fig. 8.65). The cordlike ovarian ligaments attach the inferior aspect of the ovaries to the lateral surface of the uterus and uterine tubes (Figs. 8.60, 8.64, 8.65, and 8.69). The suspensory ligament attaches the superior aspect of the ovaries to the lateral sides of the pelvic wall and contains the ovarian vessels (Figs. 8.60, 8.64, 8.65, and 8.69). The ovaries are responsible for the production of ova and the production and secretion of estrogens and progesterone. Estrogens are responsible for the development and maintenance of female characteristics and reproductive organs. Progesterone is responsible for the uterine changes in preparation for pregnancy, such as the thickening of the uterine lining and decreasing the contractions of the uterine muscles.
A follicular cyst represents the mature oocyte and its surrounding follicular cavity. Fluid increases within the cavity as the oocyte matures. A follicular cyst occurs when the graafian follicle fails to rupture and release its egg. They generally resolve spontaneously after two or three menstrual cycles.
Uterine Tubes. The uterine (fallopian) tubes are slender, muscular tubes (approximately 8-20 cm long) extending laterally from the body of the uterus to the peritoneum near the ovaries (Figs. 8.60, 8.64, and 8.65). They are supported by the broad ligament and at their distal end expand to form a funnel-shaped infundibulum. The infundibulum has numerous 1- to 2-cm fingerlike projections called fimbriae, which spread loosely over the surface of the ovaries (Figs. 8.60 and 8.65). During ovulation, the fimbriae trap the ovum and sweep it into the uterine tubes for transport to the uterus. The proximal portion of the uterine tubes open into the uterus at the cornua, and the distal portion opens directly into the peritoneal cavity, immediately superior to the ovaries, thereby providing a direct route for pathogens to enter the pelvic cavity.
Vagina. The vagina is an 8- to 10-cm muscular tube extending anteroinferiorly from the cervix of the uterus to the external vaginal orifice. The vaginal vault or fornix is the expanded upper vaginal area that surrounds the cervical os like a ring and is commonly divided into anterior and posterior fornices. The vagina is located between the bladder and the rectum and functions as a receptacle for sperm and as the lower portion of the birth canal (Figs. 8.57-8.61 and 8.72-8.75).
Pelvic Spaces. A peritoneal fold called the broad ligament encloses the ovaries, uterine tubes, and uterus (Figs. 8.64, 8.65, 8.69, and 8.72). The broad ligament extends from the sides of the uterus to the walls and floor of the pelvis, preventing side-to-side movement of the uterus and dividing the pelvis into anterior and posterior pouches. The anterior vesicouterine pouch is located between the uterus and the posterior wall of the bladder, whereas the posterior rectouterine pouch (pouch of Douglas) lies between the uterus and rectum (Figs. 8.58, 8.76, and 8.77). In males, the peritoneum is reflected from the rectum over the seminal vesicles and bladder to create the rectovesical pouch, located between the rectum and bladder (Figs. 8.79 and 8.80). The pelvic spaces are common areas for the accumulation of fluid within the pelvis. Another space in the pelvis is the retropubic space, which is located between the pubic bones and the bladder and contains extraperitoneal fat and connective tissue for the expansion of the bladder (Figs. 8.77, 8.78, and 8.80).
Male Reproductive Organs
The principal structures of the male reproductive system are the testis, epididymis, vas deferens, ejaculatory duct, seminal vesicle, prostate gland, bulbourethral gland, and penis. All these structures, except the testes and penis, are located within the pelvic cavity (Figs. 8.79 and 8.80).
Scrotum. The scrotum is a musculotendinous pouch that encloses the testis, epididymis, and lower portions of the spermatic cord (Figs. 8.79-8.81). It is composed of three fascial layers and a connective tissue layer embedded with smooth muscle fibers called the dartos tunica. Internally, the dartos tunica forms a septum that divides the scrotum into right and left compartments (median raphe), each containing a testis (Figs. 8.81 and 8.82). The scrotum facilitates sperm formation by distending the testes outside the peritoneum in a cooler environment, in effect regulating the temperature of the testes. In cold temperatures, the dartos tunica responds by constricting and pulling the testis closer to the body. This gives the scrotum its wrinkled appearance.
Testes and Epididymis. The paired testes are suspended in the fleshy, pouchlike scrotal sacs by the spermatic cords. Each testis is an ovoid organ that produces sperm and the male sex hormone, testosterone (Figs. 8.83 and 8.84). The outer fibrous covering of the testes is the tunica albuginea, which also projects into each organ to create wedge-shaped lobules. Each testis is made up of several hundred lobules, with each lobule containing 1 to 4 seminiferous tubules, approximately 800 seminiferous tubules in total. This is where spermatogenesis occurs. The seminiferous tubules leave their respective lobule and converge in an area called the rete testis. From here, about 15 to 20 ductules leave the rete testis to enter the head of the epididymis (Fig. 8.83). The epididymis is a tightly coiled tubular structure located on the superoposterior surface of each testis. The head of the epididymis is located on the upper pole of each testis, whereas the body courses along the posterior surface to the tail, which is located under the lower pole of each testis. Sperm are transmitted from the testis to the epididymis, where they are stored as they undergo the final stages of maturation (Figs. 8.79 and 8.81-8.87).
Vas Deferens (Ductus) and Ejaculatory Duct. As a continuation from the tail of the epididymis, the vas deferens is a long muscular tube that ascends in the posterior portion of the spermatic cord and traverses the inguinal canal, exiting at the deep inguinal ring (Figs. 8.81 and 8.88). It then leaves the spermatic cord and passes along the lateral pelvic wall over the ureter to the posterior surface of the bladder, where it broadens and becomes the ampulla of the vas deferens. Near its proximal end, it joins with the duct of the seminal vesicle to form the ejaculatory duct, which empties into the prostatic urethra. Each vas deferens, along with a testicular artery and vein, is surrounded by the tough connective tissue and muscle of the paired spermatic cords (Fig. 8.81).
Spermatic Cords. The spermatic cords begin at the deep inguinal ring, extend through the inguinal canal, and exit via the superficial inguinal ring to suspend the testes in the scrotum (Figs. 8.81, 8.82, and 8.89-8.92). Within the spermatic cord is the pampiniform plexus, a group of interconnected veins that drain the blood from the testicles (Figs. 8.81 and 8.83). The pampiniform plexus cools the blood in the testicular artery before it enters the testes, helping to maintain a temperature that is conducive for optimal sperm production.
Seminal Vesicles. The seminal vesicles are paired accessory glands consisting of coiled tubes that form two pouches, lateral to the vas deferens on the postero-inferior surface of the bladder. They lie superior to the prostate gland and produce fructose and a coagulating enzyme for the seminal fluid that mixes with sperm prior to ejaculation (Figs. 8.79, 8.80, 8.88, and 8.93-8.96).
Prostate Gland. The prostate gland is an extraperitoneal fibromuscular structure and is the largest accessory gland of the male reproductive system. It secretes a thin, slightly alkaline fluid that forms a portion of the seminal fluid. The prostate gland is located inferior to the bladder and surrounds the prosthetic urethra, which courses through the anterior portion of the gland (Figs. 8.79, 8.80, 8.96, and 8.97). The prostate gland has a base adjacent to the neck of the bladder and an apex that is in contact with the perineal membrane. The prostate gland is composed of glandular and fibromuscular tissue and surrounded by a capsule composed of collagen, elas- tin, and smooth muscle. It can be divided into two lateral lobes, a middle lobe, and an anterior fibromuscular portion. The ejaculatory ducts, which are extensions of the seminal vesicles, descend within the central zone of the gland and open into the prostatic urethra at the verumontanum. The verumontanum is a longitudinal mucosal fold that forms an elliptical segment of the prostatic urethra, marking the point where the ejaculatory ducts enter the urethra (Fig. 8.98). The glandular tissue comprises two-thirds of the prostate’s parenchymal tissue and can be divided into zonal anatomy in sectional imaging. The four main regions are the central, peripheral, transition, and anterior fibromuscular stroma (Figs. 8.98-8.100). The central zone is located at the base of the prostate between the peripheral and transition zones and accounts for approximately 25% of the glandular tissue. It surrounds the ejaculatory ducts and narrows to an apex at the verumontanum. The peripheral zone is the larger of the zones, comprising approximately 70% of the glandular tissue. It extends from the base to the apex along the posterior or rectal surface of the gland and surrounds the distal urethra. The peripheral zone is separated from the central and transition zones by a visible linear boundary referred to as the prostatic pseudocapsule or surgical capsule. The transition zone forms only 5% of the glandular tissue. It consists of two small lobules that are located lateral to the proximal urethra between the verumontanum and the neck of the bladder. This is the portion of the glandular tissue that enlarges due to benign prostatic hypertrophy. The periurethral zone comprises less than 1% of the glandular tissue. It is found embedded along the smooth muscular wall of the urethra. The anterior fibromuscular stroma is devoid of glandular tissue and is composed of fibrous and muscular elements. As it extends laterally and posteriorly, it thins to form the fibrous capsule that surrounds the prostate gland.
Cancer of the prostate gland is the second most common type of cancer in men, occurring with increasing frequency after the age of 55 years with an average age of 65 at time of diagnosis. According to the American Cancer Society, about 1 man in 7 will be diagnosed with prostate cancer during his lifetime.
Bulbourethral Glands. The two small, bulbourethral glands (Cowper glands) lie posterolateral to the membranous urethra, embedded in the perineal membrane. These glands secrete an alkaline fluid, which forms a portion of the seminal fluid, into the membranous urethra (Fig. 8.101).
Penis. The penis, the external reproductive organ, is attached to the pubic arch via suspensory ligaments. It has two parts: the root, which is attached to the pubic arch, and the body, which remains free. Three cylindrical masses of erectile tissue constitute the root of the penis: two corpora cavernosa and the corpus spongiosum. Each corpus cavernosum consists of a network of collagen fibers and spaces that become enlarged when filled with blood, contributing to an erection. The corpus spongiosum consists mostly of a dense venous plexus and also contributes to an erection. The two corpora cavernosa form the upper surface, whereas the corpus spongiosum forms the undersurface and contains the greater part of the urethra. At the root of the penis, the corpora cavernosa form the crura, which attach along the ischiopubic ramus. The corpus spongiosum forms the bulb of the penis, which is located between the two crura and is firmly attached to the inferior aspect of the perineal membrane. The distal end of the cylindrical masses forms the glans penis, which surrounds the external urethral meatus (Figs. 8.88 and 8.101-8.105).
VASCULATURE
Arteries
The abdominal aorta descends into the pelvis anterior to the lumbar vertebrae, slightly to the left of midline. Extending from the dorsal wall of the aorta, just above the aortic bifurcation at the level of the fourth lumbar vertebra, is the median (middle) sacral artery, which continues caudally in front of the sacrum to the apex of the coccyx. The descending aorta bifurcates into the right and left common iliac arteries (Figs. 8.106-8.108). Each common iliac artery bifurcates at the upper margin of the sacroiliac joint into the internal and external iliac arteries (Fig. 8.109). The smaller internal iliac artery extends posteromedially into the pelvis just medial to the external iliac vein and branches into an anterior trunk and a posterior trunk. The anterior trunk of the internal iliac artery supplies blood to the perineum, gluteal region, and pelvic viscera. Branches of the anterior trunk of the internal iliac artery include the obturator, umbilical, and inferior vesical arteries in males; the uterine and vaginal arteries in females; and the middle rectal, internal pudendal, and inferior gluteal arteries (Fig. 8.107). The posterior trunk of the internal iliac artery supplies blood to the posterior and lateral walls of the pelvis, iliac crest, and gluteal region. Branches of the posterior trunk include the iliolumbar, lateral sacral, and superior gluteal arteries. The large external iliac artery does not enter the true pelvis but extends along the pelvic brim to exit the iliac fossa and course under the inguinal ligament to supply the leg. The external iliac artery becomes the femoral artery at approximately the level of the anterior superior iliac spine. Branches of the external iliac artery include the inferior epigastric artery, which supplies blood to the muscles and skin of the anterior abdominal wall, and the deep circumflex iliac artery, which supplies blood to the lateral abdominal muscles (Figs. 8.110-8.120 and Table 8.2).
FIG. 8.117 MRA of descending aorta and iliac vessels.
FIG. 8.118 3D CTA of descending aorta and iliac vessels.
FIG. 8.119 Anterior oblique 3D CTA of descending aorta and iliac vessels.
FIG. 8.120 3D CTA of iliac vessels.
TABLE 8.2 Branches of the Internal and External Iliac Arteries
|
Arterial Branch |
Structures Supplied |
|
Anterior Branch of Internal Iliac |
|
|
Obturator artery |
Medial thigh Superior bladder and vas deferens |
|
Umbilical artery |
|
|
Uterine artery |
Uterus, cervix, and vagina |
|
Vaginal artery |
Vagina, posteroinferior bladder, and pelvic part of urethra |
|
Inferior vesical artery |
Prostate gland, seminal vesicles, and posteroinferior part of the bladder |
|
Middle rectal artery |
Distal end of rectum, prostate, and seminal vesicles or vagina |
|
Internal pudendal artery |
Anal canal and perineum |
|
Inferior gluteal artery Posterior Branch of Internal Iliac |
Muscles and skin of the buttock and posterior surface of the thigh |
|
Iliolumbar artery |
Psoas, iliacus, quadratus lumborum, gluteal muscles, and cauda equina |
|
Lateral sacral artery |
Spinal meninges, roots of the sacral nerves, and muscles and skin of dorsal sacrum |
|
Superior gluteal artery |
Obturator internus, piriformis, and gluteus muscles |
|
Branches of External Iliac Artery Inferior epigastric artery |
Ascends abdomen to anastomose with internal thoracic vessels to supply the anterior abdominal wall |
|
Deep circumflex iliac artery |
Ascends abdomen to anastomose with internal thoracic vessels to supply the lateral aspect of the anterior |
|
abdominal wall |
|
Venous Drainage
Venous drainage of the pelvis follows a pattern similar to that of the arterial supply. Mainly, the internal iliac veins and their tributaries drain the pelvis (Figs. 8.121 and 8.122). However, there is some drainage through the superior rectal, median (middle) sacral, and gonadal veins. The internal iliac vein ascends the pelvis medial to the internal iliac artery as it returns blood from the pelvic viscera. Tributaries of the internal iliac vein are similar to those of the branches of the internal iliac artery but with some differences, such as the iliolumbar vein, which usually drains into the common iliac vein. In addition, venous plexuses are formed by the veins in the pelvis and unite to drain mainly into the internal iliac vein (Fig. 8.122). These plexuses include the uterine, vaginal, prostatic, vesical, and rectal. The external iliac veins, extensions of the femoral veins, return blood from the legs. Typically, both external iliac veins course medial to their respective external iliac artery and then change to a posterior position as they ascend to join the common iliac vein at approximately the level of the sacroiliac joint. The common iliac vein arises posterior to the common iliac artery from the junction of the internal and external iliac veins. The inferior vena cava is formed at the level of L5, just a little to the right of the midline, by the union of the common iliac veins. From this level, it continues to ascend the abdomen to the right of the abdominal aorta (Figs. 8.108-8.115 and 8.122).
LYMPH NODES
Pelvic lymph nodes include nodal chains or groups that accompany their corresponding vessels. The nodal groups that correspond to pelvic vessels include the common iliac, internal iliac, external iliac, and sacral nodal groups (Fig. 8.123). The common iliac lymph nodes form two groups along the surface of the common iliac artery: a lateral group and a median group. The lateral common iliac group receives lymph from the lower limb and pelvis via the external and internal iliac lymph nodes. The median common iliac group receives lymph directly from the pelvic viscera and indirectly through the internal iliac and sacral lymph nodes. The obturator nodes, which course along the midportion of the obturator internus muscle, are included in the medial common iliac group. The external iliac lymph nodes lie on the external iliac vessels and drain lymph from the lower limb, abdominal wall, bladder, and prostate in males or uterus and vagina in females. The internal iliac lymph nodes surround the internal iliac vessels and their branches. They receive lymph from all the pelvic viscera, deep parts of the perineum, and gluteal and thigh regions. Sacral lymph nodes lie along the median and lateral sacral arteries. They receive lymph from the posterior pelvic wall, rectum, neck of the bladder, and prostate or cervix. The inguinal lymph nodes drain lymph from the lower limb, perineum, and anterior abdominal wall as far superiorly as the umbilicus, gluteal region, and parts of the anal canal. They can be divided into the superficial inguinal lymph nodes, which are situated distal to the inguinal ligament in the subcutaneous tissue anterior and medial to common femoral vessels, and the deep inguinal lymph nodes, which are fewer in number and are situated medial to the femoral vessels at the approximate level of the ischial tuberosity. Pelvic lymph nodes are considered pathologically enlarged when they exceed 10 mm in the short axis (Figs. 8.124-8.126).
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