Eric R. Sokol
Rene Genadry
Jean R. Anderson
• Although the basic facts of anatomy do not change, our understanding of specific anatomic relationships and the development of new clinical and surgical correlations continue to evolve.
• There is significant variation in the branching pattern of pelvic blood vessels between individuals, and patterns of blood flow may be asymmetric from side to side in the same individual. The pelvic surgeon should be prepared for deviations from “textbook” vascular patterns.
• An understanding of the development of pelvic floor disorders and their safe and effective management requires a comprehensive knowledge of the interrelationships between the bony pelvis and its ligaments, pelvic muscles and fasciae, nerves and blood vessels, and pelvic viscera.
• Approximately 10% of infants are born with some abnormality of the genitourinary system, and anomalies in one system are often mirrored by anomalies in another system that provide special implications in pelvic surgery.
• About 75% of all iatrogenic injuries to the ureter result from gynecologic procedures, most commonly abdominal hysterectomy; risk is increased with distortions of pelvic anatomy, including adnexal masses, endometriosis, other pelvic adhesive disease, or fibroids.
An understanding of the anatomy of the female pelvis is fundamental to the knowledge base of a practicing gynecologist. Although the basic facts of anatomy and their relevance to gynecologic practice do not change with time, our understanding of specific anatomic relationships and the development of new clinical and surgical correlations continue to evolve.
The anatomy of the fundamental supporting structures of the pelvis, including the genital, urinary, and gastrointestinal viscera, are presented in this chapter. Because significant variation has developed in the names of many common anatomic structures, the terms used here reflect current nomenclature according to the Nomina Anatomica; other commonly accepted terms are included in parentheses (1).
Pelvic Structure
Bony Pelvis
The skeleton of the pelvis is formed by the sacrum and coccyx and the paired hipbones (coxal, innominate), which fuse anteriorly to form the symphysis pubis. Figure 5.1 illustrates the bony pelvis as well as its ligaments and foramina.
Figure 5.1 The female pelvis. The pelvic bones (the innominate bone, sacrum, and coccyx) and their joints, ligaments, and foramina.
Sacrum and Coccyx
The sacrum and coccyx are an extension of the vertebral column resulting from the five fused sacral vertebrae and the four fused coccygeal vertebrae. They are joined by a symphyseal articulation (sacrococcygeal joint), which allows some movement.
The essential features of the sacrum and coccyx are as follows:
1. Sacral promontory—the most prominent and anterior projection of the sacrum, this is an important landmark for insertion of a laparoscope and for sacrocolpopexy. It is located just below the level of bifurcation of the common iliac arteries.
2. Four paired anterior and posterior sacral foramina—exit sites for the anterior and posterior rami of the corresponding sacral nerves; the lateral sacral vessels also traverse the anterior foramina.
3. Sacral hiatus—results from incomplete fusion of the posterior lamina of the fifth sacral vertebra, offering access to the sacral canal, which is clinically important for caudal anesthesia.
Laterally, the alae (“wings”) of the sacrum offer auricular surfaces that articulate with the hipbones to form synovial sacroiliac joints.
Os Coxae
The paired os coxae, or hipbones, have three components: the ilium, the ischium, and the pubis. These components meet to form the acetabulum, a cup-shaped cavity that accommodates the femoral head.
Ilium
1. Iliac crest—provides attachments to the iliac fascia, abdominal muscles, and fascia lata.
2. Anterior superior and inferior spine—superior spine provides the point of fixation of the inguinal ligament and is clinically important as a lateral landmark for laparoscopic entry.
3. Posterior superior and inferior spine—superior spine is the point of attachment for the sacrotuberous ligament and the posterior sacral iliac ligament.
4. Arcuate line—marks the pelvic brim and lies between the first two segments of the sacrum.
5. Iliopectineal eminence (linea terminalis)—the junction line of the ilium and the pubis.
6. Iliac fossa—the smooth anterior concavity of the ilium, covered by the iliacus muscle.
Ischium
1. Ischial spine—delineates the greater and lesser sciatic notch above and below it. It is the point of fixation for the sacrospinous ligament and the arcus tendineus fascia pelvis (white line); the ischial spine represents an important landmark in the performance of pudendal nerve block and sacrospinous ligament vaginal suspension; vaginal palpation during labor allows detection of progressive fetal descent.
2. Ischial ramus—joins the pubic rami to encircle the obturator foramen; provides the attachment for the inferior fascia of the urogenital diaphragm and the perineal musculofascial attachments.
3. Ischial tuberosity—the rounded bony prominence upon which the body rests in the sitting position; a clinical landmark for the passage of the inferior arm of anterior vaginal mesh kit systems.
Pubis
1. Body—formed by the midline fusion of the superior and inferior pubic rami.
2. Symphysis pubis—a fibrocartilaginous symphyseal joint where the bodies of the pubis meet in the midline, allows for some resilience and flexibility, which is critical during parturition.
3. Superior and inferior pubic rami—join the ischial rami to encircle the obturator foramen; provide the origin for the muscles of the thigh and leg; provide the attachment for the inferior layer of the urogenital diaphragm; the inferior rami is a clinical landmark for transobturator incontinence sling passage.
4. Pubic tubercle—a lateral projection from the superior pubic ramus, to which the inguinal ligament, rectus abdominis, and pyramidalis attach.
Clinical Considerations
Studies using magnetic resonance imaging (MRI) or computed tomography (CT) pelvimetry found an association between the architecture of the bony pelvis, specifically a wider transverse inlet (distance between the most superior aspects of the iliopectineal line) and a shorter obstetric conjugate (shortest distance between the sacral promontory and the pubic symphysis), and the occurrence of pelvic floor disorders (2,3). A loss of lumbar lordosis and a pelvic inlet that is less vertically oriented is more common in women who develop genital prolapse than in those who do not (4,5). A less vertical orientation of the pelvic inlet is thought to result in an alteration of the intra-abdominal forces that are normally directed anteriorly to the pubic symphysis such that a greater proportion is directed toward the pelvic viscera and their connective tissue and muscular supports. It is theorized that women with a wide pelvic inlet are more likely to develop pelvic organ prolapse (2,3). It is speculated that women with these characteristics may be more likely to suffer neuromuscular and connective tissue injuries during labor and delivery, predisposing them to the development of pelvic neuropathy, pelvic organ prolapse, or both. One MRI study, in which only white women were enrolled to remove race as a potential confounder, found that bony pelvis dimensions were similar at the level of the muscular pelvic floor with and without pelvic organ prolapse (6).
Pelvic Bone Articulations
The pelvic bones are joined by four articulations (two pairs):
1. Two cartilaginous symphyseal joints—the sacrococcygeal joint and the symphysis pubis—these joints are surrounded by strong ligaments anteriorly and posteriorly, which are responsive to the effect of relaxin and facilitate parturition.
2. Two synovial joints—the sacroiliac joints—these joints are stabilized by the sacroiliac ligaments, the iliolumbar ligament, the lateral lumbosacral ligament, the sacrotuberous ligament, and the sacrospinous ligament.
The pelvis is divided into the greater and lesser pelvis by an oblique plane passing through the sacral promontory, the linea terminalis (arcuate line of the ilium), the pectineal line of the pubis, the pubic crest, and the upper margin of the symphysis pubis. This plane lies at the level of the superior pelvic aperture (pelvic inlet) or pelvic brim. The inferior pelvic aperture or pelvic outlet is irregularly bound by the tip of the coccyx, the symphysis pubis, and the ischial tuberosities. The dimensions of the superior and inferior pelvic apertures have important obstetric implications.
Ligaments
Four ligaments—inguinal, Cooper's, sacrospinous, and sacrotuberous—of the bony pelvis are of special importance to the gynecologic surgeon.
Inguinal Ligament
The inguinal ligament is important surgically in the repair of inguinal hernia. The inguinal ligament:
1. Is formed by the lower border of the aponeurosis of the external oblique muscle folded back upon itself.
2. Is fused laterally to the iliacus fascia and inferiorly to the fascia lata.
3. Flattens medially into the lacunar ligament, which forms the medial border of the femoral ring.
Cooper’s Ligament
Cooper’s ligament is used frequently in bladder suspension procedures. Cooper’s ligament:
1. Is a strong ridge of fibrous tissue extending along the pectineal line—also known as the pectineal ligament.
2. Merges laterally with the iliopectineal ligament and medially with the lacunar ligament.
Sacrospinous Ligament
The sacrospinous ligament is often used for vaginal suspension. This ligament offers the advantage of a vaginal surgical route. The sacrospinous ligament:
1. Extends from the ischial spine to the lateral aspect of the sacrum.
2. Is separated from the rectovaginal space by the rectal pillars.
3. Lies anterior to the pudendal nerve and the internal pudendal vessels at its attachment to the ischial spine.
The inferior gluteal artery, with extensive collateral circulation, is found between the sacrospinous and sacrotuberous ligaments and may be injured during sacrospinous suspension (Fig. 5.2) (7). Injury to the inferior gluteal artery, and to the pudendal nerve and internal pudendal vessels, during sacrospinous ligament suspension may be minimized by careful and controlled retraction and suture placement at least two fingerbreadths medial to the ischial spine.
Figure 5.2 Tone drawing of left hemipelvis with sacrospinous ligament reflected. a., artery; Inf., inferior; lig., ligament; n., nerve; Sacrosp., sacrospinous; Sacrotub., sacrotuberous. (Redrawn from Thompson JR, Gibbs JS, Genadry R, et al. Anatomy of pelvic arteries adjacent to the sacrospinous ligament: importance of the coccygeal branch of the inferior gluteal artery. Obstet Gynecol 1999;94:973–977, with permission.)
Sacrotuberous Ligament
The sacrotuberous ligament is sometimes used as a point of fixation for vaginal vault suspension. The sacrotuberous ligament:
1. Extends from the ischial tuberosity to the lateral aspect of the sacrum.
2. Merges medially with the sacrospinous ligament.
3. Lies posterior to the pudendal nerve and the internal pudendal vessels.
Foramina
The bony pelvis and its ligaments delineate three important foramina that allow the passage of the various muscles, nerves, and vessels to the lower extremity.
Greater Sciatic Foramen
The greater sciatic foramen transmits the following structures: the piriformis muscle, the superior gluteal nerves and vessels, the sciatic nerve along with the nerves of the quadratus femoris, the inferior gluteal nerves and vessels, the posterior cutaneous nerve of the thigh, the nerves of the obturator internus, and the internal pudendal nerves and vessels.
Lesser Sciatic Foramen
The lesser sciatic foramen transmits the tendon of the obturator internus to its insertion on the greater trochanter of the femur. The nerve of the obturator internus and the pudendal vessels and nerves reenter the pelvis through the lesser sciatic foramen.
Obturator Foramen
The obturator foramen transmits the obturator nerves and vessels. The obturator neurovascular bundle can be injured during transobturator tape placement, a procedure for treatment of urinary incontinence. Trocar-based mesh kits for anterior and apical vaginal prolapse are often passed through the obturator membrane, just lateral to the descending ischiopubic ramus but medial to the obturator foramen. Injury to the obturator nerves and vessels can be prevented during these procedures by careful identification of anatomic landmarks and placement away from the obturator foramen.
Muscles
The muscles of the pelvis include those of the lateral wall and those of the pelvic floor (Fig. 5.3; Table 5.1).
Table 5.1 Muscles of the Pelvic Floor
Figure 5.3 The pelvic diaphragm. A: A view into the pelvic floor that illustrates the muscles of the pelvic diaphragm and their attachments to the bony pelvis. B: A view from outside the pelvic diaphragm illustrating the divisions of the levator ani muscles (superficial plane removed on the right). C: A lateral, sagittal view of the pelvic diaphragm and superior fascia of the urogenital diaphragm. The muscles include the deep transverse perineal and sphincter urethrae.
Lateral Wall
The muscles of the lateral pelvic wall pass into the gluteal region to assist in thigh rotation and adduction. They include the piriformis, the obturator internus, and the iliopsoas.
Pelvic Floor
Pelvic Diaphragm
The pelvic diaphragm is a funnel-shaped fibromuscular partition that forms the primary supporting structure for the pelvic contents (Fig. 5.4). It is composed of the levator ani (pubococcygeus, puborectalis, iliococcygeus) and the coccygeus muscles, along with their superior and inferior fasciae (Table 5.1). It forms the ceiling of the ischiorectal fossa.
Figure 5.4 The ligaments and fascial support of the pelvic viscera.
Levator Ani
The levator ani muscles are composed of the pubococcygeus (including the pubovaginalis and pubourethralis, puborectalis, and the iliococcygeus). The levator ani is a broad, curved sheet of muscle stretching anteriorly from the pubis and posteriorly from the coccyx and from one side of the pelvis to the other. It is perforated by the urethra, vagina, and anal canal. Its origin is from the tendinous arch extending from the body of the pubis to the ischial spine. This tendineus arch, called the arcus tendineus levator ani, is formed by a thickening of the obturator fascia and serves as a lateral landmark and point of attachment for some vaginal suspension procedures. The levator ani is inserted into the central tendon of the perineum, the wall of the anal canal, the anococcygeal ligament, the coccyx, and the vaginal wall.
The levator ani assists the anterior abdominal wall muscles in containing the abdominal and pelvic contents. It supports the vagina, facilitates defecation, and aids in maintaining fecal continence. During parturition, the levator ani supports the fetal head while the cervix dilates. The anterior portion of the levator ani complex serves to close the urogenital hiatus and pull the urethra, vagina, perineum, and anorectum toward the pubic bone, whereas the horizontally oriented posterior portion (levator plate) serves as a supportive diaphragm or “backstop” behind the pelvic viscera. Loss of normal levator ani tone, through denervation or direct muscle trauma, results in laxity of the urogenital hiatus, loss of the horizontal orientation of the levator plate, and a more bowl-like configuration. These changes can be bilateral or asymmetric (8). Such configurations are seen more often in women with pelvic organ prolapse than in those with normal pelvic organ support (9).
Traditional teaching is that the levator ani muscles are innervated by the pudendal nerve on the perineal surface and direct branches of the sacral nerves on the pelvic surface. Evidence indicates that the levator ani muscles are innervated solely by a nerve traveling on the superior (intrapelvic) surface of the muscles without the contribution of the pudendal nerve (10–15). This nerve, referred to as the levator ani nerve, originates from S3, S4, and/or S5 and innervates both the coccygeus and the levator ani muscle complex (10). After exiting the sacral foramina, it travels 2 to 3 cm medial to the ischial spine and arcus tendineus levator ani across the coccygeus, iliococcygeus, pubococcygeus, and puborectalis. Occasionally, a separate nerve comes directly from S5 to innervate the puborectalis muscle independently. Given its location, the levator ani nerve is susceptible to injury through parturition and pelvic surgery, such as during sacrospinous or iliococcygeus vaginal vault suspensions.
Urogenital Diaphragm
The muscles of the urogenital diaphragm anteriorly reinforce the pelvic diaphragm and are intimately related to the vagina and the urethra. They are enclosed between the inferior and superior fascia of the urogenital diaphragm. The muscles include the deep transverse perineal and sphincter urethrae (Table 5.1).
Blood Vessels
The pelvic blood vessels supply genital structures as well as the following:
• Urinary and gastrointestinal tracts
• Muscles of the abdominal wall, pelvic floor and perineum, buttocks, and upper thighs
• Fasciae, other connective tissue, and bones
• Skin and other superficial structures
Classically, vessels supplying organs are known as visceral vessels and those supplying supporting structures are called parietal vessels.
Major Blood Vessels
The course of the major vessels supplying the pelvis is illustrated in Figure 5.5; their origin, course, branches, and venous drainage are presented in Table 5.2. In general, the venous system draining the pelvis closely follows the arterial supply and is named accordingly. Not infrequently, a vein draining a particular area may form a plexus with multiple channels. Venous systems, which are paired, mirror each other in their drainage patterns, with the notable exception of the ovarian veins. Unusual features of venous drainage are also listed in Table 5.2.
Table 5.2 The Major Blood Vessels of the Pelvis
Figure 5.5 The blood supply to the pelvis. A: The sagittal view of the pelvis without the viscera. B: The blood supply to one pelvic viscera.
General Principles
“Control blood supply” and “maintain meticulous hemostasis” are two of the most common exhortations to young surgeons. In developing familiarity with the pattern of blood flow in the pelvis, several unique characteristics of this vasculature should be understood because of their potential implications to surgical practice:
1. The pelvic vessels play an important role in pelvic support. They provide condensations of endopelvic fascia that act to reinforce the normal position of pelvic organs (16).
2. There is significant anatomic variation between individuals in the branching pattern of the internal iliac vessels. There is no constant order in which branches divide from the parent vessel; some branches may arise as common trunks or may spring from other branches rather than from the internal iliac. Occasionally, a branch may arise from another vessel entirely (e.g., the obturator artery may arise from the external iliac or inferior epigastric artery). This variation may be found in the branches of other major vessels; the ovarian arteries are reported to arise from the renal arteries or as a common trunk from the front of the aorta on occasion. The inferior gluteal artery may originate from the posterior or the anterior branch of the internal iliac (hypogastric) artery. Patterns of blood flow may be asymmetric from side to side, and structures supplied by anastomoses of different vessels may show variation from person to person in the proportion of vascular support provided by the vessels involved (16). The pelvic surgeon must be prepared for deviations from “textbook” vascular patterns.
3. The pelvic vasculature is a high-volume, high-flow system with enormous expansive capabilities throughout reproductive life. Blood flow through the uterine arteries increases to about 500 mL per min in late pregnancy. In nonpregnant women, certain conditions, such as uterine fibroids or malignant neoplasms, may be associated with neovascularization and hypertrophy of existing vessels and a corresponding increase in pelvic blood flow. Understanding the volume and flow characteristics of the pelvic vasculature in different clinical situations will enable the surgeon to anticipate problems and take appropriate preoperative and intraoperative measures (including blood and blood product availability) to prevent or manage hemorrhage.
4. The pelvic vasculature is supplied with an extensive network of collateral connections that provides a rich anastomotic communication between different major vessel systems (Fig. 5.6). This degree of redundancy is important to ensure adequate supply of oxygen and nutrients in the event of major trauma or other vascular compromise. Hypogastric artery ligation continues to be used as a strategy for management of massive pelvic hemorrhage when other measures have failed. Bilateral hypogastric artery ligation, particularly when combined with ovarian artery ligation, dramatically reduces pulse pressure in the pelvis, converting flow characteristics from that of an arterial system to a venous system and allowing use of collateral channels of circulation to continue blood supply to pelvic structures. The significance of collateral blood flow is demonstrated by reports of successful pregnancies occurring after bilateral ligation of both hypogastric and ovarian arteries (17). Table 5.3 lists the collateral channels of circulation in the pelvis.
Table 5.3 Collateral Arterial Circulation of the Pelvis
|
Primary Artery |
Collateral Arteries |
|
Aorta |
|
|
Ovarian artery |
Uterine artery |
|
Superior rectal artery (inferior mesenteric artery) |
Middle rectal artery |
|
Inferior rectal artery (internal pudendal) |
|
|
Lumbar arteries |
Iliolumbar artery |
|
Vertebral arteries |
Iliolumbar artery |
|
Middle sacral artery |
Lateral sacral artery |
|
External Iliac |
|
|
Deep iliac circumflex artery |
Iliolumbar artery |
|
Superior gluteal artery |
|
|
Inferior epigastric artery |
Obturator artery |
|
Femoral |
|
|
Medial femoral circumflex artery |
Obturator artery |
|
Inferior gluteal artery |
|
|
Lateral femoral circumflex artery |
Superior gluteal artery |
|
Iliolumbar artery |
|
Figure 5.6 The collateral blood vessels of the pelvis. (Modified from Kamina P. Anatomie gynécologique et obstétricale. Paris, France: Maloine Sa Éditeur, 1984:125, with permission.)
Special Vascular Considerations
To avoid injury to vascular structures and resultant hemorrhage while inserting a trocar into the anterior abdominal wall during laparoscopy, the surgeon should keep in mind certain anatomic relationships. The inferior epigastric artery is a branch of the external iliac artery, arising from the parent vessel at the medial border of the inguinal ligament and coursing cephalad lateral to and posterior to the rectus sheath at the level of the arcuate line. It lies about 1.5 cm lateral to the medial umbilical fold, which marks the site of the obliterated umbilical artery. During laparoscopy the inferior epigastric artery almost always can be visualized between the obliterated umbilical artery medially and the insertion of the round ligament through the inguinal canal laterally. This artery can be traced visually cephalad, allowing for safe insertion of lateral port site. The aortic bifurcation occurs at the level of L4 to L5, just above the sacral promontory. Palpation of the sacral promontory to guide trocar insertion allows the surgeon to avoid the major vascular structures in this area (see Fig. 23.4 in Chapter 23). The left common iliac vein lies medial to the artery and is at risk of injury during umbilical laparoscopic trocar insertion and during dissection for sacrocolpopexy.
Lymphatics
The pelvic lymph nodes are generally arranged in groups or chains and follow the course of the larger pelvic vessels, for which they are usually named. Smaller nodes that lie close to the visceral structures are usually named for those organs. Lymph nodes in the pelvis receive afferent lymphatic vessels from pelvic and perineal visceral and parietal structures and send efferent lymphatics to more proximal nodal groups. The number of lymph nodes and their exact location is variable; however, certain nodes tend to be relatively constant:
1. Obturator node in the obturator foramen, close to the obturator vessels and nerve
2. Nodes at the junction of the internal and external iliac veins
3. Ureteral node in the broad ligament near the cervix, where the uterine artery crosses over the ureter
4. The Cloquet or Rosenmüller node—the highest of the deep inguinal nodes that lies within the opening of the femoral canal
Figure 5.7 illustrates the pelvic lymphatic system. Table 5.4 outlines the major lymphatic chains of relevance to the pelvis and their primary afferent connections from major pelvic and perineal structures. There are extensive interconnections between lymph vessels and nodes; usually more than one lymphatic pathway is available for drainage of each pelvic site. Bilateral and crossed extension of lymphatic flow may occur, and entire groups of nodes may be bypassed to reach more proximal chains.
Table 5.4 Primary Lymph Node Groups Providing Drainage to Genital Structures
|
Nodes |
Primary Afferent Connections |
|
Aortic/para-aortic |
Ovary, fallopian tube, uterine corpus (upper); drainage from common iliac nodes |
|
Common iliac |
Drainage from external and internal iliac nodes |
|
External iliac |
Upper vagina, cervix, uterine corpus (upper); drainage from inguinal |
|
Internal iliac |
Upper vagina, cervix, uterine corpus (lower) |
|
Lateral sacral |
|
|
Superior gluteal |
|
|
Inferior gluteal |
|
|
Obturator |
|
|
Vesical |
|
|
Rectal |
|
|
Parauterine |
|
|
Inguinal |
Vulva, lower vagina; (rare: uterus, tube, ovary) |
|
Superficial |
|
|
Deep |
Figure 5.7 The lymphatic drainage of the female pelvis. The vulva and lower vagina drain to the superficial and deep inguinal nodes, sometimes directly to the iliac nodes (along the dorsal vein of the clitoris) and to the other side. The cervix and upper vagina drain laterally to the parametrial, obturator, and external iliac nodes and posteriorly along the uterosacral ligaments to the sacral nodes. Drainage from these primary lymph node groups is upward along the infundibulopelvic ligament, similar to drainage of the ovary and fallopian tubes to the para-aortic nodes. The lower uterine body drains in the same manner as the cervix. Rarely, drainage occurs along the round ligament to the inguinal nodes.
The natural history of most genital tract malignancies directly reflects the lymphatic drainage of those structures, although the various interconnections, different lymphatic paths, and individual variability make the spread of malignancy somewhat unpredictable. Regional lymph node metastasis is one of the most important factors in formulation of treatment plans for gynecologic malignancies and prediction of eventual outcome.
Nerves
The pelvis is innervated by both the autonomic and somatic nervous systems. The autonomic nerves include both sympathetic (adrenergic) and parasympathetic (cholinergic) fibers and provide the primary innervation for genital, urinary, and gastrointestinal visceral structures and blood vessels.
Somatic Innervation
The lumbosacral plexus and its branches provide motor and sensory somatic innervation to the lower abdominal wall, the pelvic and urogenital diaphragms, the perineum, and the hip and lower extremity (Fig. 5.8). The nerves originating from the muscles, the lumbosacral trunk, the anterior divisions of the upper four sacral nerves (sacral plexus), and the anterior division of the coccygeal nerve and fibers from the fourth and fifth sacral nerves (coccygeal plexus) are found on the anterior surface of the piriformis muscle and lateral to the coccyx, respectively, deep in the posterior pelvis. In Table 5.5 each major branch is listed by spinal segment and structures innervated. In addition to these branches, the lumbosacral plexus includes nerves that innervate muscles of the lateral pelvic wall (obturator internus, piriformis), posterior hip muscles, and the pelvic diaphragm. A visceral component, the pelvic splanchnic nerve, is included.
Table 5.5 Lumbosacral Plexus
|
Nerve |
Spinal Segment |
Innervation[MB2][MB2] |
|
Iliohypogastric |
T12, L1 |
Sensory—skin near iliac crest, just above symphysis pubis |
|
Ilioinguinal |
L1 |
Sensory—upper medial thigh, mons, labia majora |
|
Lateral femoral cutaneous |
L2, L3 |
Sensory—lateral thigh to level of knee |
|
Femoral |
L2, L3, L4 |
Sensory—anterior and medial thigh, medial leg and foot, hip and knee joints |
|
Genitofemoral |
L1, L2 |
Sensory—anterior vulva (genital branch), middle/upper anterior thigh (femoral branch) |
|
Obturator |
L2, L3, L4 |
Sensory—medial thigh and leg, hip and knee joints |
|
Superior gluteal |
L4, L5, S1 |
Motor—gluteal muscles |
|
Inferior gluteal |
L4, L5, S1, S2 |
Motor—gluteal muscles |
|
Posterior femoral cutaneous |
S1, S2, S3 |
Sensory—vulva, perineum, posterior thigh |
|
Sciatic |
L4, L5, S1, S2, S3 |
Sensory—much of leg, foot, lower-extremity joints |
|
Pudendal |
S2, S3, S4 |
Sensory—perianal skin, vulva and perineum, clitoris, urethra, vaginal vestibule |
Figure 5.8 The sacral plexus. (Modified from Kamina P. Anatomie gynécologique et obstétricale. Paris, France: Maloine Sa Éditeur, 1984:90, with permission.)
Nerves supplying the cutaneous aspects of the anterior, medial, and lateral lower extremities, and the deep muscles of the anterior thigh, primarily leave the pelvis by passing beneath the inguinal ligament. Nerves supporting the posterior cutaneous and deep structures of the hip, thigh, and leg lie deep in the pelvis and should not be vulnerable to injury during pelvic surgery. The obturator nerve travels along the lateral pelvic wall to pass through the obturator foramen into the upper thigh, and it may be encountered in more radical dissections involving the lateral pelvic wall, in paravaginal repairs, or in trocar-based incontinence and prolapse procedures.
The pudendal nerve innervates the striated urethral and anal sphincters and the deep and superficial perineal muscles and provides sensory innervation to the external genitalia. This nerve originates from S2–S4, crosses over the piriformis to travel with the internal pudendal vessels into the ischiorectal fossa through the lesser sciatic foramen, and travels through the pudendal canal (Alcock’s canal) on the medial aspect of the obturator internus muscles, where it divides into its three terminal branches to provide the primary innervation to the perineum. Other nerves contribute to the cutaneous innervation of the perineum:
1. The anterior labial nerve branches of the ilioinguinal nerve—these nerves emerge from within the inguinal canal and through the superficial inguinal ring to the mons and upper labia majora.
2. The genital branch of the genitofemoral nerve—this branch enters the inguinal canal with the round ligament and passes through the superficial inguinal ring to the anterior vulva.
3. The perineal branches of the posterior femoral cutaneous nerve—after leaving the pelvis through the greater sciatic foramen, these branches run in front of the ischial tuberosity to the lateral perineum and labia majora.
4. Perforating cutaneous branches of the second and third sacral nerves—these branches perforate the sacrotuberous ligament to supply the buttocks and contiguous perineum.
5. The anococcygeal nerves—these nerves arise from S4 to S5 and also perforate the sacrotuberous ligament to supply the skin overlying the coccyx.
Autonomic Innervation
Functionally, the innervation of the pelvic viscera may be divided into an efferent component and an afferent, or sensory, component. In reality, afferent and efferent fibers are closely associated in a complex interlacing network and cannot be separated anatomically.
Efferent Innervation
Efferent fibers of the autonomic nervous system, unlike motor fibers in the somatic system, involve one synapse outside the central nervous system, with two neurons required to carry each impulse. In the sympathetic(thoracolumbar) division, this synapse is generally at some distance from the organ being innervated; conversely, the synapse is on or near the organ of innervation in the parasympathetic (craniosacral) division.
Axons from preganglionic neurons emerge from the spinal cord to make contact with peripheral neurons arranged in aggregates known as autonomic ganglia. Some of these ganglia, along with interconnecting nerve fibers, form a pair of longitudinal cords called the sympathetic trunks. Located lateral to the spinal column from the base of the cranium to the coccyx, the sympathetic trunks lie along the medial border of the psoas muscle from T12 to the sacral prominence and then pass behind the common iliac vessels to continue into the pelvis on the anterior surface of the sacrum. On the anterolateral surface of the aorta, the aortic plexus forms a lacy network of nerve fibers with interspersed ganglia. Rami arising from or traversing the sympathetic trunks join this plexus and its subsidiaries.
The ovaries, part of the fallopian tubes, and broad ligament are innervated by the ovarian plexus, a network of nerve fibers accompanying the ovarian vessels and derived from the aortic and renal plexuses. The inferior mesenteric plexus is a subsidiary of the celiac plexus and aortic plexus and is located along the inferior mesenteric artery and its branches, providing innervation to the left colon, sigmoid, and rectum.
The superior hypogastric plexus (presacral nerve) is the continuation of the aortic plexus beneath the peritoneum in front of the terminal aorta, the fifth lumbar vertebra, and the sacral promontory, medial to the ureters (Fig. 5.9). Embedded in loose areolar tissue, the plexus overlies the middle sacral vessels and is usually composed of two or three incompletely fused trunks. It contains preganglionic fibers from lumbar nerves, postganglionic fibers from higher sympathetic ganglia and the sacral sympathetic trunks, and visceral afferent fibers. Just below the sacral promontory, the superior hypogastric plexus divides into two loosely arranged nerve trunks, the hypogastric nerves.These nerves course inferiorly and laterally to connect with the inferior hypogastric plexuses (pelvic plexuses), which are a dense network of nerves and ganglia that lie along the lateral pelvic sidewall overlying branches of the internal iliac vessels (Fig. 5.9).
Figure 5.9 The presacral nerves.
The inferior hypogastric plexus includes efferent sympathetic fibers, afferent (sensory) fibers, and parasympathetic fibers arising from the pelvic splanchnic nerves (S2 to S4, nervi erigentes).
This paired plexus is the final common pathway of the pelvic visceral nervous system and is divided into three portions, representing distribution of innervation to the viscera:
1. Vesical plexus
• Innervation: bladder and urethra
• Course: along vesical vessels
2. Middle rectal plexus (hemorrhoidal)
• Innervation: rectum
• Course: along middle rectal vessels
3. Uterovaginal plexus (Frankenhäuser ganglion)
• Innervation: uterus, vagina, clitoris, vestibular bulbs
• Course: along uterine vessels and through cardinal and uterosacral ligaments; sympathetic and sensory fibers derive from T10, L1; parasympathetic fibers derive from S2 to S4.
Afferent Innervation
Afferent fibers from the pelvic viscera and blood vessels traverse the same pathways to provide sensory input to the central nervous system. They are involved in reflex arcs needed for bladder, bowel, and genital tract function. The afferent fibers reach the central nervous system to have their first synapse within the posterior spinal nerve ganglia.
Presacral neurectomy, in which a segment of the superior hypogastric plexus is divided and resected in order to interrupt sensory fibers from the uterus and cervix, is associated with relief of dysmenorrhea secondary to endometriosis in about 50% to 75% of cases in which it was used (18,19). Efferent fibers from the adnexa travel with the ovarian plexus; thus, pain originating from the ovary or tube is not relieved by resection of the presacral nerve. Because this plexus contains efferent sympathetic and parasympathetic nerve fibers intermixed with afferent fibers, disturbance in bowel or bladder function may result. An alternative surgical procedure is resection of a portion of the uterosacral ligaments; because they contain numerous nerve fibers with more specific innervation to the uterus, it is postulated that bladder and rectal function is less vulnerable to compromise (20).
An anesthetic block of the pudendal nerve is performed most often for pain relief with uncomplicated vaginal deliveries but may provide useful anesthesia for minor perineal surgical procedures.This nerve block may be accomplished transvaginally or through the perineum. A needle is inserted toward the ischial spine with the tip directed slightly posteriorly and through the sacrospinous ligament. As the anesthetic agent is injected, frequent aspiration is required to avoid injection into the pudendal vessels, which travel with the nerve.
Pelvic Viscera
Embryonic Development
The female urinary and genital tracts are closely related, anatomically and embryologically. Both are derived largely from primitive mesoderm and endoderm, and there is evidence that the embryologic urinary system has an important inductive influence on the developing genital system. About 10% of infants are born with some abnormality of the genitourinary system, and anomalies in one system are often mirrored by anomalies in another system (19).
Developmental defects may play a significant role in the differential diagnosis of certain clinical signs and symptoms and have special implications in pelvic surgery (21–26). Thus it is important for gynecologists to have a basic understanding of embryology.
Following is a presentation of the urinary system, internal reproductive organs, and external genitalia in order of their initial appearance, although much of this development occurs concurrently. The development of each of these three regions proceeds synchronously at an early embryologic age (Table 5.6).
Table 5.6 Development of Genital and Urinary Tracts by Embryologic Age
|
Weeks of Gestation |
Genital Development |
Urinary Development |
|
4–6 |
Urorectal septum |
Pronephros |
|
Formation of cloacal folds, genital tubercle |
Mesonephros/mesonephric duct |
|
|
Ureteric buds, metanephros |
||
|
Genital ridges |
Exstrophy of mesonephric ducts and ureters into bladder wall |
|
|
6–7 |
End of indifferent phase of genital development |
Major, minor calyces form |
|
Development of primitive sex cords |
Kidneys begin to ascend |
|
|
Formation of paramesonephric ducts |
||
|
Labioscrotal swellings |
||
|
8–11 |
Distal paramesonephric ducts begin to fuse |
Kidney becomes functional |
|
Formation of sinuvaginal bulbs |
||
|
12 |
Development of clitoris and vaginal vestibule |
|
|
20 |
Canalization of vaginal plate |
|
|
32 |
Renal collecting duct system complete |
Urinary System
Kidneys, Renal Collecting System, Ureters
The kidneys, renal collecting system, and ureters derive from the longitudinal mass of mesoderm (known as the nephrogenic cord) found on each side of the primitive aorta. This process gives rise to three successive sets of increasingly advanced urinary structures, each developing more caudal to its predecessor.
The pronephros, or “first kidney,” is rudimentary and nonfunctional; it is succeeded by the “middle kidney,” or mesonephros, which is believed to function briefly before regressing. Although the mesonephrosis transitory as an excretory organ, its duct, the mesonephric (wolffian) duct, is of singular importance for the following reasons:
1. It grows caudally in the developing embryo to open, for the first time, an excretory channel into the primitive cloaca and the “outside world.”
2. It serves as the starting point for development of the metanephros, which becomes the definitive kidney.
3. It ultimately differentiates into the sexual duct system in the male.
4. Although regressing in female fetuses, there is evidence that the mesonephric duct may have an inductive role in development of the paramesonephric or müllerian duct (22).
The ureteric buds, which sprout from the distal mesonephric ducts, initiate the development of the metanephros; these buds extend cranially and penetrate the portion of the nephrogenic cord known as the metanephric blastema. The ureteric buds begin to branch sequentially, with each growing tip covered by metanephric blastema. Ultimately the metanephric blastema form the renal functional units (the nephrons), whereas the ureteric buds become the collecting duct system of the kidneys (collecting tubules, minor and major calyces, renal pelvis) and the ureters. Although these primitive tissues differentiate along separate paths, they are interdependent on inductive influences from each other—neither can develop alone.
The kidneys initially lie in the pelvis but subsequently ascend to their permanent location, rotating almost 90 degrees in the process as the more caudal part of the embryo in effect grows away from them. Their blood supply, which first arises as branches of the middle sacral and common iliac arteries, comes from progressively higher branches of the aorta until the definitive renal arteries form; previous vessels then regress. The definitive kidneys become functional in the late 7th to early 8th weeks of gestation.
Bladder and Urethra
The cloaca forms as the result of dilation of the opening to the fetal exterior. During the 7th week of gestation, the cloaca is partitioned by the mesenchymal urorectal septum into an anterior urogenital sinus and a posterior rectum. The bladder and urethra form from the most superior portion of the urogenital sinus, with surrounding mesenchyme contributing to their muscular and serosal layers. The remaining inferior urogenital sinus is known as the phallic or definitive urogenital sinus. Concurrently, the distal mesonephric ducts and attached ureteric buds are incorporated into the posterior bladder wall in the area that will become the bladder trigone. As a result of the absorption process, the mesonephric duct ultimately opens independently into the urogenital sinus below the bladder neck.
The allantois, which is a vestigial diverticulum of the hindgut that extends into the umbilicus and is continuous with the bladder, loses its lumen and becomes the fibrous band known as the urachus or median umbilical ligament. In rare instances, the urachal lumen remains partially patent, with formation of urachal cysts, or completely patent, with the formation of a urinary fistula to the umbilicus (23).
Genital System
Although genetic gender is determined at fertilization, the early genital system is indistinguishable between the two genders in the embryonic stage. This is known as the “indifferent stage” of genital development, during which both male and female fetuses have gonads with prominent cortical and medullary regions, dual sets of genital ducts, and external genitalia that appear similar. Male sexual differentiation is an “active” process, requiring the presence of the SRY gene (gender-determining region), located on the short arm of the Y chromosome. Clinically, gender is not apparent until about the 12th week of embryonic life and depends on the elaboration of testis-determining factor and, subsequently, androgens by the male gonad. Female development is called the “basic developmental path of the human embryo,” requiring not estrogen but the absence of testosterone.
Internal Reproductive Organs
The primordial germ cells migrate from the yolk sac through the mesentery of the hindgut to the posterior body wall mesenchyme at about the 10th thoracic level, which is the initial site of the future ovary (Figs. 5.10 and 5.11). Once the germ cells reach this area, they induce proliferation of cells in the adjacent mesonephros and celomic epithelium to form a pair of genital ridges medial to the mesonephros. This occurs during the 5th week of gestation. The development of the gonad is absolutely dependent on this proliferation because these cells form a supporting aggregate of cells (the primitive sex cords) that invest the germ cells and without which the gonad would degenerate.
Figure 5.10 The comparative changes of the female and male during early embryonic development.
Figure 5.11 The embryonic development of the female genital tract. The formation of the uterus and vagina. A: The uterus and superior end of the vagina begin to form as the paramesonephric ducts fuse together near their attachment to the posterior wall of the primitive urogenital sinus. B, C: The ducts then zipper together in a superior direction between the 3rd and 5th months. As the paramesonephric ducts are pulled away from the posterior body wall, they drag a fold of peritoneal membrane with them, forming the broad ligaments of the uterus. A–C: The inferior end of the vagina forms from the sinovaginal bulbs on the posterior wall of the primitive urogenital sinus.
Müllerian Ducts
The paramesonephric or müllerian ducts form lateral to the mesonephric ducts; they grow caudally and then medially to fuse in the midline. They contact the urogenital sinus in the region of the posterior urethra at a slight thickening known as the sinusal tubercle. Subsequent sexual development is controlled by the presence or absence of testis-determining factor, encoded on the Y chromosome and elaborated by the somatic sex cord cells. Testis-determining factor causes the degeneration of the gonadal cortex and differentiation of the medullary region of the gonad into Sertoli cells.
The Sertoli cells secrete a glycoprotein known as anti-müllerian hormone (AMH), which causes regression of the paramesonephric duct system in the male embryo and is the likely signal for differentiation of Leydig cells from the surrounding mesenchyme. The Leydig cells produce testosterone and, with the converting enzyme 5α-reductase, dihydrotestosterone. Testosterone is responsible for evolution of the mesonephric duct system into the vas deferens, epididymis, ejaculatory ducts, and seminal vesicle. At puberty, testosterone leads to spermatogenesis and changes in primary and secondary sex characteristics. Dihydrotestosterone triggers the development of the male external genitalia and the prostate and bulbourethral glands. In the absence of testis-determining factor, the medulla regresses, and the cortical sex cords break up into isolated cell clusters (the primordial follicles).
The germ cells differentiate into oogonia and enter the first meiotic division as primary oocytes, at which point development is arrested until puberty. In the absence of AMH, the mesonephric duct system degenerates, although in at least one-fourth of adult women, remnants may be found in the mesovarium (epoophoron, paroophoron) or along the lateral wall of the uterus or vagina (Gartner duct cyst) (24).
The paramesonephric duct system subsequently develops. The inferior fused portion becomes the uterovaginal canal, which later becomes the epithelium and glands of the uterus and the upper vagina. The endometrial stroma and myometrium differentiate from surrounding mesenchyme. The cranial unfused portions of the paramesonephric ducts open into the celomic (future peritoneal) cavity and become the fallopian tubes.
The fusion of the paramesonephric ducts brings together two folds of peritoneum, which become the broad ligament and divide the pelvic cavity into a posterior rectouterine and anterior vesicouterine pouch or cul-de-sac. Between the leaves of the broad ligament, mesenchyme proliferates and differentiates into loose areolar connective tissue and smooth muscle.
Vagina
The vagina forms in the 3rd month of embryonic life. While the uterovaginal canal is forming, the endodermal tissue of the sinusal tubercle begins to proliferate, forming a pair of sinovaginal bulbs, which become the inferior 20% of the vagina. The most inferior portion of the uterovaginal canal becomes occluded by a solid core of tissue (the vaginal plate), the origin of which is unclear. Over the subsequent 2 months, this tissue elongates and canalizes by a process of central desquamation, and the peripheral cells become the vaginal epithelium. The fibromuscular wall of the vagina originates from the mesoderm of the uterovaginal canal.
Accessory Genital Glands
The female accessory genital glands develop as outgrowths from the urethra (paraurethral or Skene) and the definitive urogenital sinus (greater vestibular or Bartholin). Although the ovaries first develop in the thoracic region, they ultimately arrive in the pelvis by a complicated process of descent. This descent by differential growth is under the control of a ligamentous cord called the gubernaculum, which is attached to the ovary superiorly and to the fascia in the region of the future labia majora inferiorly. The gubernaculum becomes attached to the paramesonephric ducts at their point of superior fusion so that it becomes divided into two separate structures. As the ovary and its mesentery (the mesovarium) are brought into the superior portion of the broad ligament, the more proximal part of the gubernaculum becomes the ovarian ligament, and the distal gubernaculum becomes the round ligament.
External Genitalia
Early in the 5th week of embryonic life, folds of tissue form on each side of the cloaca and meet anteriorly in the midline to form the genital tubercle (Fig. 5.12). With the division of the cloaca by the urorectal septum and consequent formation of the perineum, these cloacal folds are known anteriorly as the urogenital folds and posteriorly as the anal folds. The genital tubercle begins to enlarge. In the female embryo, its growth gradually slows to become the clitoris, and the urogenital folds form the labia minora. In the male embryo, the genital tubercle continues to grow to form the penis, and the urogenital folds are believed to fuse to enclose the penile urethra. Lateral to the urogenital folds, another pair of swellings develops, known in the indifferent stage as labioscrotal swellings. In the absence of androgens, they remain largely unfused to become the labia majora. The definitive urogenital sinus gives rise to the vaginal vestibule, into which open the urethra, vagina, and greater vestibular glands.
Figure 5.12 The comparative development of the female and male external genitalia. A: In both sexes, the development follows a uniform pattern through the 7th week and thereafter begins to differentiate. B: The male external genitalia. C: The female external genitalia.
Clinical Correlations
Developmental abnormalities of the urinary and genital systems can be explained and understood by a consideration of female and male embryologic development. Because of the intertwined development of these two systems, abnormalities in one may be associated with abnormalities in the other (25).
Urinary System
Urinary-tract anomalies arise from defects in the ureteric bud, the metanephric blastema, or their inductive interaction with each other.
Renal Agenesis
Renal agenesis occurs when one or both ureteric buds fail to form or degenerate, and the metanephric blastema is therefore not induced to differentiate into nephrons. Bilateral renal agenesis is incompatible with postnatal survival, but infants with only one kidney usually survive, and the single kidney undergoes compensatory hypertrophy. Unilateral renal agenesis is often associated with absence or abnormality of fallopian tubes, uterus, or vagina—the paramesonephric duct derivatives.
Abnormalities of Renal Position
Abnormalities of renal position result from disturbance in the normal ascent of the kidneys. A malrotated pelvic kidney is the most common result; a horseshoe kidney, in which the kidneys are fused across the midline, occurs in about 1 in 600 individuals and has a final position lower than usual because its normal ascent is prevented by the root of the inferior mesenteric artery.
Duplication of the Upper Ureter and Renal Pelvis
Duplication of the upper ureter and renal pelvis is relatively common and results from premature bifurcation of the ureteric bud. If two ureteric buds develop, there will be complete duplication of the collecting system. In this situation, one ureteric bud will open normally into the posterior bladder wall, and the second bud will be carried more distally within the mesonephric duct to form an ectopic ureteral orifice into the urethra, vagina, or vaginal vestibule; incontinence is the primary presenting symptom. Most of the aforementioned urinary abnormalities remain asymptomatic unless obstruction or infection supervenes. In that case, anomalous embryologic development must be included in the differential diagnosis.
Genital System
Because the early development of the genital system is similar in both sexes, congenital defects in sexual development, usually arising from a variety of chromosomal abnormalities, tend to present clinically with ambiguous external genitalia. These conditions are known as intersex conditions or hermaphroditism and are classified according to the histologic appearance of the gonads.
True Hermaphroditism
Individuals with true hermaphroditism have both ovarian and testicular tissue, most commonly as composite ovotestes but occasionally with an ovary on one side and a testis on the other. In the latter case, a fallopian tube and single uterine horn may develop on the side with the ovary because of the absence of local AMH. True hermaphroditism is an extremely rare condition associated with chromosomal mosaicism, mutation, or abnormal cleavage involving the X and Y chromosomes.
Pseudohermaphroditism
In individuals with pseudohermaphroditism, the genetic gender indicates one gender, whereas the external genitalia have characteristics of the other gender. Males with pseudohermaphroditism are genetic males with feminized external genitalia, most commonly manifesting as hypospadias (urethral opening on the ventral surface of the penis) or incomplete fusion of the urogenital or labioscrotal folds. Females with pseudohermaphroditism are genetic females with virilized external genitalia, including clitoral hypertrophy and some degree of fusion of the urogenital or labioscrotal folds. Both types of pseudohermaphroditism are caused either by abnormal levels of sex hormones or abnormalities in the sex hormone receptors.
Another major category of genital tract abnormalities involves various types of uterovaginal malformations, which occur in 0.16% of women (Fig. 5.13) (26). These malformations are believed to result from one or more of the following situations:
Figure 5.13 Types of congenital abnormalities. A: Double uterus (uterus didelphys) and double vagina. B: Double uterus with single vagina. C: Bicornuate uterus. D: Bicornuate uterus with a rudimentary left horn. E: Septate uterus. F: Unicornuate uterus.
1. Improper fusion of the paramesonephric ducts
2. Incomplete development of one paramesonephric duct
3. Failure of part of the paramesonephric duct on one or both sides to develop
4. Absent or incomplete canalization of the vaginal plate
Genital Structures
Vagina
A sagittal section of the female pelvis is presented in Fig. 5.14.
Figure 5.14 The pelvic viscera. A sagittal section of the female pelvis with the pelvic viscera and their relationships.
The vagina is a hollow fibromuscular tube extending from the vulvar vestibule to the uterus. In the dorsal lithotomy position, the vagina is directed posteriorly toward the sacrum, but its axis is almost horizontal in the upright position. It is attached at its upper end to the uterus just above the cervix. The spaces between the cervix and vagina are known as the anterior, posterior, and lateral vaginal fornices.Because the vagina is attached at a higher point posteriorly than anteriorly, the posterior vaginal wall is about 3 cm longer than the anterior wall.
The posterior vaginal fornix is separated from the posterior cul-de-sac and peritoneal cavity by the vaginal wall and peritoneum. This proximity is clinically useful, both diagnostically and therapeutically. Culdocentesis, a technique in which a needle is inserted just posterior to the cervix through the vaginal wall into the peritoneal cavity, is used to evaluate intraperitoneal hemorrhage (e.g., ruptured ectopic pregnancy, hemorrhagic corpus luteum, other intraabdominal bleeding), pus (e.g., pelvic inflammatory disease, ruptured intra-abdominal abscess), or other intra-abdominal fluid (e.g., ascites). Incision into the peritoneal cavity from this location in the vagina, known as a posterior colpotomy, can be used as an adjunct to laparoscopic excision of adnexal masses, with removal of the mass intact through the posterior vagina.
The vagina is attached to the lateral pelvic wall with endopelvic fascial connections to the arcus tendineus (white line), which extends from the pubic bone to the ischial spine. This connection converts the vaginal lumen into a transverse slit with the anterior and posterior walls in apposition; the lateral space where the two walls meet is the vaginal sulcus. Lateral detachments of the vagina are recognized in some cystocele formations (lateral cystoceles or paravaginal defects).
The opening of the vagina may be covered by a membrane or surrounded by a fold of connective tissue called the hymen. This tissue is usually replaced by irregular tissue tags after sexual activity and childbirth occur. The lower vagina is somewhat constricted as it passes through the urogenital hiatus in the pelvic diaphragm; the upper vagina is more spacious. The entire vagina is characterized by its distensibility, which is most evident during childbirth.
The vagina is closely applied anteriorly to the urethra, bladder neck and trigonal region, and posterior bladder; posteriorly, the vagina lies in association with the perineal body, anal canal, lower rectum, and posterior cul-de-sac. It is separated from both the lower urinary and gastrointestinal tracts by their investing layers of fibromuscular elements known as the endopelvic fascia.
The vagina is composed of three layers:
1. Mucosa—nonkeratinized stratified squamous epithelium, without glands. Vaginal lubrication occurs primarily by transudation, with contributions from cervical and Bartholin gland secretions. The mucosa has a characteristic pattern of transverse ridges and furrows known as rugae. It is hormonally sensitive, responding to stimulation by estrogen with proliferation and maturation. The mucosa is colonized by mixed bacterial flora with lactobacillus predominant; normal pH is 3.5 to 4.5.
2. Muscularis—connective tissue and smooth muscle, loosely arranged in inner circular and outer longitudinal layers.
3. Adventitia—endopelvic fascia, adherent to the underlying muscularis.
Blood Supply
The blood supply of the vagina includes the vaginal artery and branches from the uterine, middle rectal, and internal pudendal arteries.
Innervation
The innervation of the vagina is as follows: the upper vagina—uterovaginal plexus; the distal vagina—pudendal nerve.
Uterus
The uterus is a fibromuscular organ usually divided into a lower cervix and an upper corpus or uterine body (Fig. 5.15).
Figure 5.15 The uterus, fallopian tubes, and ovaries.
Cervix
The portion of cervix exposed to the vagina is the exocervix or portio vaginalis. It has a convex round surface with a circular or slitlike opening (the external os) into the endocervical canal. The endocervical canal is about 2 to 3 cm in length and opens proximally into the endometrial cavity at the internal os.
The cervical mucosa contains both stratified squamous epithelium, characteristic of the exocervix, and mucus-secreting columnar epithelium, characteristic of the endocervical canal. The intersection where these two epithelia meet—the squamocolumnar junction—is geographically variable and dependent on hormonal stimulation. It is this dynamic interface, the transformation zone, which is most vulnerable to the development of squamous neoplasia.
In early childhood, during pregnancy, or with oral contraceptive use, columnar epithelium may extend from the endocervical canal onto the exocervix, a condition known as eversion or ectopy. After menopause, the transformation zone usually recedes entirely into the endocervical canal.
Production of cervical mucus is under hormonal influence. It varies from profuse, clear, and thin mucus around the time of ovulation to scant and thick mucus in the postovulatory phase of the cycle. Deep in the mucosa and submucosa, the cervix is composed of fibrous connective tissue and a small amount of smooth muscle in a circular arrangement.
Corpus
The body of the uterus varies in size and shape, depending on hormonal and childbearing status. At birth, the cervix and corpus are about equal in size; in adult women, the corpus has grown to two to three times the size of the cervix. The position of the uterus in relation to other pelvic structures is variable and is generally described in terms of positioning—anterior, midposition, or posterior; flexion; and version. Flexion is the angle between the long axis of the uterine corpus and the cervix, whereas version is the angle of the junction of the uterus with the upper vagina. Occasionally, abnormal positioning may occur secondary to associated pelvic pathology, such as endometriosis or adhesions.
The uterine corpus is divided into several different regions. The area where the endocervical canal opens into the endometrial cavity is known as the isthmus or lower uterine segment. On each side of the upper uterine body, a funnel-shaped area receives the insertion of the fallopian tubes and is called the uterine cornu; the uterus above this area is the fundus.
The endometrial cavity is triangular in shape and represents the mucosal surface of the uterine corpus. The epithelium is columnar and gland forming with a specialized stroma. It undergoes cyclic structural and functional change during the reproductive years, with regular shedding of the superficial endometrium and regeneration from the basal layer.
The muscular layer of the uterus, the myometrium, consists of interlacing smooth muscle fibers and ranges in thickness from 1.5 to 2.5 cm. Some outer fibers are continuous with those of the tube and round ligament.
Peritoneum covers most of the corpus of the uterus and the posterior cervix and is known as the serosa. Laterally, the broad ligament, a double layer of peritoneum covering the neurovascular supply to the uterus, inserts into the cervix and corpus. Anteriorly, the bladder lies over the isthmic and cervical region of the uterus.
Blood Supply
The blood supply to the uterus is the uterine artery, which anastomoses with the ovarian and vaginal arteries.
Innervation
The nerve supply to the uterus is the uterovaginal plexus.
Fallopian Tubes
The fallopian tubes and ovaries collectively are referred to as the adnexa. The fallopian tubes are paired hollow structures representing the proximal unfused ends of the müllerian duct. They vary in length from 7 to 12 cm, and their function includes ovum pickup, provision of physical environment for conception, and transport and nourishment of the fertilized ovum.
The tubes are divided into several regions:
1. Interstitial—narrowest portion of the tube, lies within the uterine wall and forms the tubal ostia at the endometrial cavity.
2. Isthmus—narrow segment closest to the uterine wall.
3. Ampulla—larger diameter segment lateral to the isthmus.
4. Fimbria (infundibulum)—funnel-shaped abdominal ostia of the tubes, opening into the peritoneal cavity; this opening is fringed with numerous fingerlike projections that provide a wide surface for ovum pickup. The fimbria ovarica is a connection between the end of the tube and ovary, bringing the two closer.
The tubal mucosa is ciliated columnar epithelium, which becomes progressively more architecturally complex as the fimbriated end is approached. The muscularis consists of an inner circular and outer longitudinal layer of smooth muscle. The tube is covered by peritoneum and, through its mesentery (mesosalpinx), which is situated dorsal to the round ligament, is connected to the upper margin of the broad ligament.
Blood Supply
The vascular supply to the fallopian tubes is the uterine and ovarian arteries.
Innervation
The innervation to the fallopian tubes is the uterovaginal plexus and the ovarian plexus.
Ovaries
The ovaries are paired gonadal structures that lie suspended between the pelvic wall and the uterus by the infundibulopelvic ligament laterally and the utero-ovarian ligament medially. Inferiorly, the hilar surface of each ovary is attached to the broad ligament by its mesentery (mesovarium), which is dorsal to the mesosalpinx and fallopian tube. Primary neurovascular structures reach the ovary through the infundibulopelvic ligament and enter through the mesovarium. The normal ovary varies in size, with measurements up to 5 × 3 × 3 cm. Variation in dimension results from endogenous hormonal production, which varies with age and with each menstrual cycle. Exogenous substances, including oral contraceptives, gonadotropin-releasing hormone agonists, or ovulation-inducing medication, may either stimulate or suppress ovarian activity and, therefore, affect size.
Each ovary consists of a cortex and medulla and is covered by a single layer of flattened cuboidal to low columnar epithelium that is continuous with the peritoneum at the mesovarium. The cortex is composed of a specialized stroma and follicles in various stages of development or attrition. The medulla occupies a small portion of the ovary in its hilar region and is composed primarily of fibromuscular tissue and blood vessels.
Blood Supply
The blood supply to the ovary is the ovarian artery, which anastomoses with the uterine artery.
Innervation
The innervation to the ovary is the ovarian plexus and the uterovaginal plexus.
Urinary Tract
Ureters
The ureter is the urinary conduit leading from the kidney to the bladder; it measures about 25 cm in length and is totally retroperitoneal in location.
The lower half of each ureter traverses the pelvis after crossing the common iliac vessels at their bifurcation, just medial to the ovarian vessels. It descends into the pelvis adherent to the peritoneum of the lateral pelvic wall and the medial leaf of the broad ligament and enters the bladder base anterior to the upper vagina, traveling obliquely through the bladder wall to terminate in the bladder trigone.
The ureteral mucosa is a transitional epithelium. The muscularis consists of an inner longitudinal and outer circular layer of smooth muscle. A protective connective tissue sheath, which is adherent to the peritoneum, encloses the ureter.
Blood Supply
The blood supply is variable, with contributions from the renal, ovarian, common iliac, internal iliac, uterine, and vesical arteries.
Innervation
The innervation is through the ovarian plexus and the vesical plexus.
Bladder and Urethra
Bladder
The bladder is a hollow organ, spherically shaped when full, that stores urine. Its size varies with urine volume, normally reaching a maximum volume of at least 300 mL. The bladder is often divided into two areas, which are of physiologic significance:
1. The base of the bladder consists of the urinary trigone posteriorly and a thickened area of detrusor anteriorly. The three corners of the trigone are formed by the two ureteral orifices and the opening of the urethra into the bladder. The bladder base receives α-adrenergic sympathetic innervation and is the area responsible for maintaining continence.
2. The dome of the bladder is the remaining bladder area above the bladder base. It has parasympathetic innervation and is responsible for micturition.
The bladder is positioned posterior to the pubis and lower abdominal wall and anterior to the cervix, upper vagina, and part of the cardinal ligament. Laterally, it is bounded by the pelvic diaphragm and obturator internus muscle.
The bladder mucosa is transitional cell epithelium and the muscle wall (detrusor). Rather than being arranged in layers, it is composed of intermeshing muscle fibers.
Blood Supply
The blood supply to the bladder is from the superior, middle, and inferior vesical arteries, with contribution from the uterine and vaginal vessels.
Innervation
The innervation to the bladder is from the vesical plexus, with contribution from the uterovaginal plexus.
Urethra
The vesical neck is the region of the bladder that receives and incorporates the urethral lumen. The female urethra is about 3 to 4 cm in length and extends from the bladder to the vestibule, traveling just anterior to the vagina.
The urethra is lined by nonkeratinized squamous epithelium that is responsive to estrogen stimulation. Within the submucosa on the dorsal surface of the urethra are the paraurethral or Skene glands, which empty through ducts into the urethral lumen. Distally, these glands empty into the vestibule on either side of the external urethral orifice. Chronic infection of Skene glands, with obstruction of their ducts and cystic dilation, is believed to be an inciting factor in the development of suburethral diverticula.
The urethra contains an inner longitudinal layer of smooth muscle and outer, circularly oriented smooth muscle fibers. The inferior fascia of the urogenital diaphragm or perineal membrane begins at the junction of the middle and distal thirds of the urethra. Proximal to the middle and distal parts of the urethra, voluntary muscle fibers derived from the urogenital diaphragm intermix with the outer layer of smooth muscle, increasing urethral resistance and contributing to continence. At the level of the urogenital diaphragm, the skeletal muscle fibers leave the wall of the urethra to form the sphincter urethrae and deep transverse perineal muscles. In the coronal plane on MRI studies, the ventral urogenital diaphragm forms an interconnected complex with the compressor urethrae, vestibular bulb, and levator ani. The dorsal part connects the levator ani and vaginal sidewall via a distinct band to the ischiopubic ramus. In the sagittal plane the parallel position of urogenital diaphragm and levator ani can be seen (27).
Blood Supply
The vascular supply to the urethra is from the vesical and vaginal arteries and the internal pudendal branches.
Innervation
The innervation to the urethra is from the vesical plexus and the pudendal nerve.
The lower urinary and genital tracts are intimately connected anatomically and functionally. In the midline, the bladder and proximal urethra can be dissected easily from the underlying lower uterine segment, cervix, and vagina through a loose avascular plane. The distal urethra is essentially inseparable from the vagina. Of surgical significance is the location of the bladder trigone immediately over the middle third of the vagina. Unrecognized injury to the bladder during pelvic surgery may result in development of a vesicovaginal fistula.
Dissection to the level of the trigone is rarely required, and damage to this critical area is unusual.
Lower Gastrointestinal Tract
Sigmoid Colon
The sigmoid colon begins its characteristic S-shaped curve as it enters the pelvis at the left pelvic brim (Fig. 5.16). The columnar mucosa and richly vascularized submucosa are surrounded by an inner circular layer of smooth muscle and three overlying longitudinal bands of muscle called tenia coli. A mesentery of varying length attaches the sigmoid to the posterior abdominal wall.
Figure 5.16 The rectosigmoid colon, its vascular supply, and muscular support. (Coronal view: peritoneum removed on right.)
Blood Supply
The blood supply to the sigmoid colon is from the sigmoid arteries.
Innervation
The nerves to the sigmoid colon are derived from the inferior mesenteric plexus.
Rectum
The sigmoid colon loses its mesentery in the midsacral region and becomes the rectum about 15 to 20 cm above the anal opening. The rectum follows the curve of the lower sacrum and coccyx and becomes entirely retroperitoneal at the level of the rectouterine pouch or posterior cul-de-sac. It continues along the pelvic curve just posterior to the vagina until the level of the anal hiatus of the pelvic diaphragm, at which point it takes a sharp 90-degree turn posteriorly and becomes the anal canal, separated from the vagina by the perineal body.
The rectal mucosa is lined by a columnar epithelium and characterized by three transverse folds that contain mucosa, submucosa, and the inner circular layer of smooth muscle. The tenia of the sigmoid wall broaden and fuse over the rectum to form a continuous longitudinal external layer of smooth muscle to the level of the anal canal.
Anal Canal
The anal canal begins at the level of the sharp turn in the direction of the distal colon and is 2 to 3 cm in length. At the anorectal junction, the mucosa changes to stratified squamous epithelium (the pectinate line), which continues until the termination of the anus at the anal verge, where there is a transition to perianal skin with typical skin appendages. It is surrounded by a thickened ring of circular muscle fibers that are a continuation of the circular muscle of the rectum, the internal anal sphincter. Its lower part is surrounded by bundles of striated muscle fibers, the external anal sphincter (28).
Fecal continence is provided primarily by the puborectalis muscle and the internal and external anal sphincters. The puborectalis surrounds the anal hiatus in the pelvic diaphragm and interdigitates posterior to the rectum to form a rectal sling. The external anal sphincter surrounds the terminal anal canal below the level of the levator ani. A growing body of literature suggests that both external anal sphincter and levator ani muscles are important for fecal continence and that multiple injuries contribute to pelvic floor dysfunction (29,30)[MB1] One such MRI study showed that major levator ani muscle injuries were observed in 19.1% women who delivered vaginally with external anal sphincter injuries, 3.5% who delivered vaginally without external anal sphincter injury, and none of the women who delivered by cesarean section before labor. Among women with external anal sphincter injuries, those with major levator ani muscle injuries trended more toward fecal incontinence (29). Further studies suggest that thickening of the internal anal sphincter occurs with aging, and that thinning of the external anal sphincter and a corresponding drop in squeeze pressure correlated with fecal incontinence, but not aging (31).
The anatomic proximity of the lower gastrointestinal tract to the lower genital tract is particularly important during surgery of the vulva and vagina. Lack of attention to this proximity during repair of vaginal lacerations or episiotomies can lead to damage of the rectum and fistula formation or injury to the external anal sphincter, resulting in fecal incontinence. Because of the avascular nature of the rectovaginal space, it is relatively easy to dissect the rectum from the vagina in the midline, which is routinely done in the repair of rectoceles.
Blood Supply
The vascular supply to the rectum and anal canal is from the superior, middle, and inferior rectal arteries. The venous drainage is a complex submucosal plexus of vessels that, under conditions of increased intra-abdominal pressure (pregnancy, pelvic mass, chronic constipation, ascites), may dilate and become symptomatic with rectal bleeding or pain as hemorrhoids.
Innervation
The nerve supply to the anal canal is from the middle rectal plexus, the inferior mesenteric plexus, and the pudendal nerve.
The Genital Tract and Its Relations
The genital tract is situated at the bottom of the intra-abdominal cavity and is related to the intraperitoneal cavity and its contents, the retroperitoneal spaces, and the pelvic floor. Accessing it through the abdominal wall or the perineum requires a thorough knowledge of the anatomy of these areas and their relationships.
The Abdominal Wall
The anterior abdominal wall is bound superiorly by the xiphoid process and the costal cartilage of the 7th to 10th ribs and inferiorly by the iliac crest, anterosuperior iliac spine, inguinal ligament, and pubic bone. It consists of skin, muscle, fascia, and nerves and vessels.
Skin
The lower abdominal skin may exhibit striae, or “stretch marks,” and increased pigmentation in the midline in parous women. The subcutaneous tissue contains a variable amount of fat.
Muscles
Five muscles and their aponeuroses contribute to the structure and strength of the anterolateral abdominal wall (Fig. 5.17; Table 5.7).
Table 5.7 Muscles Contributing to the Structure and Strength of the Anterolateral Abdominal Wall
Figure 5.17 The abdominal wall muscles.
Fascia
Superficial Fascia
The superficial fascia consists of two layers:
1. Camper fascia—the most superficial layer, which contains a variable amount of fat and is continuous with the superficial fatty layer of the perineum
2. Scarpa fascia—a deeper membranous layer continuous in the perineum with Colles fascia (superficial perineal fascia) and with the deep fascia of the thigh (fascia lata)
Rectus Sheath
The aponeuroses of the external and internal oblique and the transversus abdominis combine to form a sheath for the rectus abdominis and pyramidalis, fusing medially in the midline at the linea alba and laterally at the semilunar line (Fig. 5.18). Above the arcuate line, the aponeurosis of the internal oblique muscle splits into anterior and posterior lamella (Fig. 5.18A). Below this line, all three layers are anterior to the body of the rectus muscle (Fig. 5.18B). The rectus is covered posteriorly by the transversalis fascia, providing access to the muscle for the inferior epigastric vessels.
Figure 5.18 A transverse section of the rectus abdominis. The aponeurosis of the external and internal oblique and the transversus abdominis from the rectus abdominis. A: Above the arcuate line. B: Below the arcuate line.
Transversalis Fascia and Endopelvic Fascia
The transversalis fascia is a firm membranous sheet on the internal surface of the transversus abdominis muscle that extends beyond the muscle and forms a fascia lining the entire abdominopelvic cavity. Like the peritoneum, it is divided into a parietal and a visceral component. It is continuous from side to side across the linea alba and covers the posterior aspect of the rectus abdominis muscle below the arcuate line. Superiorly, it becomes the inferior fascia of the diaphragm. Inferiorly, it is attached to the iliac crest, covers the iliac fascia and the obturator internus fascia, and extends downward and medially to form the superior fascia of the pelvic diaphragm.
Characteristically, the transversalis fascia continues along blood vessels and other structures leaving and entering the abdominopelvic cavity and contributes to the formation of the visceral (endopelvic) pelvic fascia (32). The pelvic fascia invests the pelvic organs and attaches them to the pelvic sidewalls, thereby playing a critical role in pelvic support. In the inguinal region, the fascial relationships result in the development of the inguinal canal, through which the round ligament exits into the perineum. The fascia is separated from the peritoneum by a layer of preperitoneal fat. Areas of fascial weakness or congenital or posttraumatic and surgical injuries result in herniation of the underlying structures through a defective abdominal wall. The incisions least likely to result in damage to the integrity and innervation of the abdominal wall muscles include a midline incision through the linea alba and a transverse incision through the recti muscle fibers that respects the integrity of its innervation (33).
Nerves and Vessels
The tissues of the abdominal wall are innervated by the continuation of the inferior intercostal nerves T4 to T11 and the subcostal nerve T12. The inferior part of the abdominal wall is supplied by the first lumbar nerve through the iliohypogastric and the ilioinguinal nerves. Abdominal wall surgical sites below the level of the anterior superior iliac spine have the potential for ilioinguinal or iliohypogastric injury (34). The primary blood supply to the anterior lateral abdominal wall includes the following:
1. The inferior epigastric and deep circumflex iliac arteries, branches of the external iliac artery
2. The superior epigastric artery, a terminal branch of the internal thoracic artery
The inferior epigastric artery runs superiorly in the transverse fascia to reach the arcuate line, where it enters the rectus sheath. It is vulnerable to damage by abdominal incisions in which the rectus muscle is completely or partially transected, during placement of lateral laparoscopic ports, or by excessive lateral traction on the rectus. The deep circumflex artery runs on the deep aspect of the anterior abdominal wall parallel to the inguinal ligament and along the iliac crest between the transverse abdominis muscle and the internal oblique muscle. The superior epigastric vessels enter the rectus sheath superiorly just below the seventh costal cartilage.
The venous system drains into the saphenous vein, and the lymphatics drain to the axillary chain above the umbilicus and to the inguinal nodes below it. The subcutaneous tissues drain to the lumbar chain.
Perineum
The perineum is situated at the lower end of the trunk between the buttocks. Its bony boundaries include the lower margin of the pubic symphysis anteriorly, the tip of the coccyx posteriorly, and the ischial tuberosities laterally. These landmarks correspond to the boundaries of the pelvic outlet. The diamond shape of the perineum is customarily divided by an imaginary line joining the ischial tuberosities immediately in front of the anus, at the level of the perineal body, into an anterior urogenital and a posterior anal triangle (Fig. 5.19).
Figure 5.19 Vulva and perineum.
Urogenital Triangle
The urogenital triangle includes the external genital structures and the urethral opening (Fig. 5.19). These external structures cover the superficial and deep perineal compartments and are known as the vulva (Figs. 5.20and 5.21).
Figure 5.20 Superficial perineal compartment.
Figure 5.21 Deep perineal compartment.
Vulva
Mons Pubis
The mons pubis is a triangular eminence in front of the pubic bones that consists of adipose tissue covered by hair-bearing skin up to its junction with the abdominal wall.
Labia Majora
The labia majora are a pair of fibroadipose folds of skin that extend from the mons pubis downward and backward to meet in the midline in front of the anus at the posterior fourchette. They include the terminal extension of the round ligament and occasionally a peritoneal diverticulum, the canal of Nuck. They are covered by skin with scattered hairs laterally and are rich in sebaceous, apocrine, and eccrine glands.
Labia Minora
The labia minora lie between the labia majora, with which they merge posteriorly, and are separated into two folds anteriorly as they approach the clitoris. The anterior folds unite to form the prepuce or hood of the clitoris. The posterior folds form the frenulum of the clitoris as they attach to its inferior surface. The labia minora are covered by hairless skin overlying a fibroelastic stroma rich in neural and vascular elements. The area between the posterior labia minora forms the vestibule of the vagina.
Clitoris
The clitoris is an erectile organ that is 2 to 3 cm in length. It consists of two crura and two corpora cavernosa and is covered by a sensitive rounded tubercle (the glans).
Vaginal Orifice
The vaginal orifice is surrounded by the hymen, a variable crescentic mucous membrane that is replaced by rounded caruncles after its rupture. The opening of the duct of the greater vestibular(Bartholin) glands is located on each side of the vestibule. Numerous lesser vestibular glands are also scattered posteriorly and between the urethral and vaginal orifices.
Urethral Orifice
The urethral orifice is immediately anterior to the vaginal orifice and about 2 to 3 cm beneath the clitoris. The Skene (paraurethral) gland duct presents an opening on its posterior surface.
Superficial Perineal Compartment
The superficial perineal compartment lies between the superficial perineal fascia and the inferior fascia of the urogenital diaphragm (perineal membrane) (Fig. 5.20). The superficial perineal fascia has a superficial and deep component. The superficial layer is relatively thin and fatty and is continuous superiorly with the superficial fatty layer of the lower abdominal wall (Camper fascia). It continues laterally as the fatty layer of the thighs. The deep layer of the superficial perineal (Colles) fascia is continuous superiorly with the deep layer of the superficial abdominal fascia (Scarpa fascia), which attaches firmly to the ischiopubic rami and ischial tuberosities. The superficial perineal compartment is continuous superiorly with the superficial fascial spaces of the anterior abdominal wall, allowing spread of blood or infection along that route. Such spread is limited laterally by the ischiopubic rami, anteriorly by the transverse ligament of the perineum, and posteriorly by the superficial transverse perineal muscle. The superficial perineal compartment includes the following:
Erectile Bodies
The vestibular bulbs are 3-cm, highly vascular structures surrounding the vestibule and located under the bulbocavernosus muscle. The body of the clitoris is attached by two crura to the internal aspect of the ischiopubic rami. The crura are covered by the ischiocavernosus muscles.
Muscles
The muscles of the vulva are the ischiocavernosus, the bulbocavernosus, and superficial transverse perineal. They are included in the superficial perineal compartment as follows:
Ischiocavernosus
• Origin—ischial tuberosity
• Insertion—ischiopubic bone
• Action—compresses the crura and lowers the clitoris
Bulbocavernosus
• Origin—perineal body
• Insertion—posterior aspect of the clitoris; some fibers pass above the dorsal vein of the clitoris in a slinglike fashion
• Action—compresses the vestibular bulb and dorsal vein of the clitoris
Superficial Transverse Perineal
• Origin—ischial tuberosity
• Insertion—central perineal tendon
• Action—fixes the perineal body
Vestibular Glands
The vestibular glands are situated on either side of the vestibule under the posterior end of the vestibular bulb. They drain between the hymen and the labia minora. Their mucous secretion helps maintain adequate lubrication. Infection in these glands can result in an abscess.
Deep Perineal Compartment
The deep perineal compartment is a fascial space bound inferiorly by the perineal membrane and superiorly by a deep fascial layer that separates the urogenital diaphragm from the anterior recess of the ischiorectal fossa (Fig. 5.21). It is stretched across the anterior half of the pelvic outlet between the ischiopubic rami. The deep compartment may be directly continuous superiorly with the pelvic cavity (35). The posterior pubourethral ligaments, functioning as winglike elevations of the fascia ascending from the pelvic floor to the posterior aspect of the symphysis pubis, provide a point of fixation to the urethra and support the concept of the continuity of the deep perineal compartment with the pelvic cavity.
The anterior pubourethral ligaments represent a similar elevation of the inferior fascia of the urogenital diaphragm and are joined by the intermediate pubourethral ligament, with the junction between the two fascial structures arcing under the pubic symphysis (36). The urogenital diaphragm includes the sphincter urethrae (urogenital sphincter) and the deep transverse perineal (transversus vaginae) muscle.
The urogenital diaphragm (perineal membrane) is composed of two regions: one dorsal and one ventral. The dorsal portion consists of bilateral transverse fibrous sheets that attach the lateral wall of the vagina and perineal body to the ischiopubic ramus. This portion is devoid of striated muscle. The ventral portion is part of a solid three-dimensional tissue mass in which several structures are embedded. It is intimately associated with the compressor urethrae and the urethrovaginal sphincter muscle of the distal urethra with the urethra and its surrounding connective tissue. In this region the perineal membrane is continuous with the insertion of the arcus tendineus fascia pelvis. The levator ani muscles are connected with the cranial surface of the perineal membrane. The vestibular bulb and clitoral crus are fused with the membrane’s caudal surface (37).
The sphincter urethrae (Fig. 5.22) is a continuous muscle fanning out as it develops proximally and distally, including the following:
Figure 5.22 The complete urogenital sphincter musculature, bladder, and vagina. (Redrawn from Haderer JM, Pannu HK, Genadry R, et al. Controversies in female urethral anatomy and their significance for understanding urinary continence: observations and literature review. Int Urogynecol J Pelvic Floor Dysfunct 2002;13:236–252, with permission.)
1. The external urethral sphincter, which surrounds the middle third of the urethra
2. The compressor urethrae, arcing across the ventral side of the urethra
3. The urethrovaginal sphincter, which surrounds the ventral aspect of the urethra and terminates in the lateral vaginal wall
The deep transverse perineal muscle originates at the internal aspect of the ischial bone, parallels the muscle compressor urethrae, and attaches to the lateral vaginal wall along the perineal membrane. Studies show that a smaller striated urogenital sphincter is associated with stress incontinence and poorer pelvic floor muscle function (38).
The urinary and genital tracts have a common reliance on several interdependent structures for support. The cardinal and uterosacral ligaments are condensations of endopelvic fascia that support the cervix and upper vagina over the levator plate. Laterally, endopelvic fascial condensations attach the midvagina to the pelvic walls at the arcus tendineus fascia pelvis anteriorly and the arcus tendineus levator ani posteriorly. The distal anterior vagina and urethra are anchored to the urogenital diaphragm and the distal posterior vagina to the perineal body.
Anteriorly, the pubourethral ligaments and pubovesical fascia and ligaments provide fixation and stabilization for the urethra and bladder. Posteriorly, they rely on the vagina and lower uterus for support. Partial resection or relaxation of the uterosacral ligaments often leads to relaxation of the genitourinary complex, resulting in the formation of a cystocele. Studies indicate that half of the observed variation in anterior compartment support may be explained by apical support (39). Various types and degrees of genital tract prolapse or relaxation are almost always associated with similar findings in the bladder, urethra, or both.
There are three levels of vaginal support as described by DeLancey (Fig. 5.23) (40). Level I support consists of paracolpium that suspends the apical portion of the vagina and is comprised of the cardinal-uterosacral ligament complex. Level II support comprises the paracolpium that is attached to the vagina laterally via the arcus tendineus fasciae pelvis and superior fascia of the levator ani. Level III support consists of the distal vaginal attachments: anteriorly, via fusion of the urethra to the vagina, laterally, to the levators, and posteriorly, with the perineal body.
Figure 5.23 DeLancey levels of support[MB3].
Clinical Relevance
Disruption of level I support may lead to prolapse of the uterus or vaginal vault, while damage to level II and III supports predispose to anterior and posterior vaginal prolapse. All levels of defective support should be repaired during reconstructive surgery.
Blood Supply
The blood supply to the vulva is as follows:
1. External pudendal artery (from femoral artery), internal pudendal artery
2. Venous drainage—internal pudendal veins
The blood supply to the superficial and deep perineal compartments is as follows:
1. Internal pudendal artery, dorsal artery of the clitoris
2. Venous drainage—internal pudendal veins, which are richly anastomotic
3. Lymphatic drainage—internal iliac chain
Innervation
The innervation to the vulva is from branches of the following nerves:
1. Ilioinguinal nerve
2. Genitofemoral nerve (genital branch)
3. Lateral femoral cutaneous nerve of the thigh (perineal branch)
4. Perineal nerve (branch of pudendal)
5. Superficial and deep perineal compartments, innervated by the perineal nerve
Perineal Body
The perineal body or central perineal tendon is critical to the posterior support of the lower aspect of the anterior vaginal wall. It is a triangle-shaped structure separating the distal portion of the anal and vaginal canals that is formed by the convergence of the tendinous attachments of the bulbocavernosus, the external anal sphincter, and the superficial transverse perinei muscle. Its superior border represents the point of insertion of the rectovaginal(Denonvilliers) fascia, which extends to the underside of the peritoneum covering the cul-de-sac of Douglas, separating the anorectal from the urogenital compartment (41). The perineal body plays an important anchoring role in the musculofascial support of the pelvic floor. It represents the central connection between the two layers of support of the pelvic floor—the pelvic and urogenital diaphragm. It also provides a posterior connection to the anococcygeal raphe. Thus, it is central to the definition of the bilevel support of the floor of the pelvis.
Anal Triangle
The anal triangle includes the lower end of the anal canal. The external anal sphincter surrounds the anal triangle, and the ischiorectal fossa is on each side. Posteriorly, the anococcygeal body lies between the anus and the tip of the coccyx and consists of thick fibromuscular tissue (of levator ani and external anal sphincter origin) giving support to the lower part of the rectum and the anal canal.
The external anal sphincter forms a thick band of muscular fibers arranged in three layers running from the perineal body to the anococcygeal ligament. The subcutaneous fibers are thin and surround the anus and, without bony attachment, decussate in front of it. The superficial fibers sweep forward from the anococcygeal ligament, and the tip of the coccyx around the anus inserts into the perineal body. The deep fibers arise from the perineal body to encircle the lower half of the anal canal to form a true sphincter muscle, which fuses with the puborectalis portion of the levator ani.
The ischiorectal fossa is mainly occupied by fat and separates the ischium laterally from the median structures of the anal triangle. It is a fascia-lined space located inferiorly between the perineal skin and the pelvic diaphragm superiorly; it communicates with the contralateral ischiorectal fossa over the anococcygeal ligament. Superiorly, its apex is at the origin of the levator ani muscle from the obturator fascia. It is bound medially by the levator ani and the external sphincter with their fascial covering, laterally by the obturator internus muscle with its fascia, posteriorly by the sacrotuberous ligament and the lower border of the gluteus maximus muscle, and anteriorly by the base of the urogenital diaphragm. It is widest and deepest posteriorly and weakest medially.
An ischiorectal abscess should be drained without delay, or it will extend into the anal canal. The cavity is filled with fat that cushions the anal canal and is traversed by many fibrous bands, vessels, and nerves, including the pudendal and the inferior rectal nerves. The perforating branch of S2 and S3 and the perineal branch of S4 also run through this space.
The pudendal (Alcock) canal is a tunnel formed by a splitting of the inferior portion of the obturator fascia running anteromedially from the ischial spine to the posterior edge of the urogenital diaphragm. It contains the pudendal artery, vein, and nerve in their traverse from the pelvic cavity to the perineum.
Blood Supply
The blood supply to the anal triangle is from the inferior rectal (hemorrhoidal) artery and vein.
Innervation
The innervation to the anal triangle is from the perineal branch of the fourth sacral nerve and the inferior rectal (hemorrhoidal) nerve.
Retroperitoneum and Retroperitoneal Spaces
The subperitoneal area of the true pelvis is partitioned into potential spaces by the various organs and their respective fascial coverings and by the selective thickenings of the endopelvic fascia into ligaments and septa(Fig. 5.24). It is imperative that surgeons operating in the pelvis be familiar with these spaces, as discussed below.
Figure 5.24 Schematic sectional drawing of the pelvis shows the firm connective tissue covering. The bladder, cervix, and rectum are surrounded by a connective tissue covering. The Mackenrodt ligament extends from the lateral cervix to the lateral abdominal pelvic wall. The vesicouterine ligament originating from the anterior edge of the Mackenrodt ligament leads to the covering of the bladder on the posterior side. The sagittal rectum column spreads both to the connective tissue of the rectum and the sacral vertebrae closely nestled against the back of the Mackenrodt ligament and lateral pelvic wall. Between the firm connective tissue bundles is loose connective tissue (paraspaces). (From Von Peham H, Amreich JA. Gynaekologische Operationslehre. Berlin, Germany: S Karger, 1930, with permission.)
Prevesical Space
The prevesical (Retzius) space is a fat-filled potential space bound anteriorly by the pubic bone, covered by the transversalis fascia, and extending to the umbilicus between the medial umbilical ligaments (obliterated umbilical arteries); posteriorly, the space extends to the anterior wall of the bladder. It is separated from the paravesical space by the ascending bladder septum (bladder pillars).
Upon entering the prevesical space, the pubourethral ligaments may be seen inserting into the posterior aspect of the symphysis pubis as a thickened prolongation of the arcus tendineus fascia. With combined abdominal and vaginal bladder neck suspensory procedures, the point of entry is usually the Retzius space between the arcus tendineus and the pubourethral ligaments.
Paravesical Spaces
The paravesical spaces are fat filled and limited by the fascia of the obturator internus muscle and the pelvic diaphragm laterally, the bladder pillar medially, the endopelvic fascia inferiorly, the lateral umbilical ligament superiorly, the cardinal ligament posteriorly, and the pubic bone anteriorly.
Vesicovaginal Space
The vesicovaginal space is separated from the Retzius space by the endopelvic fascia. This space is limited anteriorly by the bladder wall (from the proximal urethra to the upper vagina), posteriorly by the anterior vaginal wall, and laterally by the bladder septa (selective thickenings of the endopelvic fascia inserting laterally into the arcus tendineus). A tear in these fascial investments and thickenings medially, transversely, or laterally allows herniation and development of a cystocele.
Rectovaginal Space
The rectovaginal space extends between the vagina and the rectum from the superior border of the perineal body to the underside of the rectouterine Douglas pouch. It is bound anteriorly by the rectovaginal septum (firmly adherent to the posterior aspect of the vagina), posteriorly by the anterior rectal wall, and laterally by the descending rectal septa separating the rectovaginal space from the pararectal space on each side. The rectovaginal septum represents a firm membranous transverse septum dividing the pelvis into rectal and urogenital compartments, allowing the independent function of the vagina and rectum and providing support for the rectum. It is fixed laterally to the pelvic sidewall by rectovaginal fascia (part of the endopelvic fascia) along a line extending from the posterior fourchette to the arcus tendineus fasciae pelvis, midway between the pubis and the ischial spine (42). An anterior rectocele often results from a defective septum or an avulsion of the septum from the perineal body. Reconstruction of the perineum is critical for the restoration of this important compartmental separation and for the support of the anterior vaginal wall (43). Lateral detachment of the rectovaginal fascia from the pelvic sidewall may constitute a “pararectal” defect analogous to anterior paravaginal defects.
Pararectal Space
The pararectal space is bound laterally by the levator ani, medially by the rectal pillars, and posteriorly above the ischial spine by the anterolateral aspect of the sacrum. It is separated from the retrorectal space by the posterior extension of the descending rectal septa.
Retrorectal Space
The retrorectal space is limited by the rectum anteriorly and the anterior aspect of the sacrum posteriorly. It communicates with the pararectal spaces laterally above the uterosacral ligaments and extends superiorly into the presacral space.
Presacral Space
The presacral space is the superior extension of the retrorectal space and is limited by the deep parietal peritoneum anteriorly and the anterior aspect of the sacrum posteriorly. It harbors the middle sacral vessels and the hypogastric plexi between the bifurcation of the aorta invested by loose areolar tissue. Presacral neurectomy requires familiarity with and working knowledge of this space. Abdominal sacrocolpopexy involves dissection in the presacral space down to the anterior longitudinal ligament, which is the point of fixation for the tail of the Y-shaped mesh graft. The surgical space is bound superiorly by the bifurcation of the great vessels and laterally by the ureter on the right and the mesentery of the sigmoid colon and the left common iliac vein on the left. The left iliac vein lies medial to the left iliac artery bounding this space and is more prone to injury during laparoscopic entry or presacral dissection.
Peritoneal Cavity
The female pelvic organs lie at the bottom of the abdominopelvic cavity covered superiorly and posteriorly by the small and large bowel. Anteriorly, the uterine wall is in contact with the posterosuperior aspect of the bladder. The uterus is held in position by the following structures:
1. The round ligaments coursing inferolaterally toward the internal inguinal ring
2. The uterosacral ligaments, which provide support to the cervix and upper vagina and interdigitate with fibers from the cardinal ligament near the cervix
3. The cardinal ligaments, which provide support to the cervix and upper vagina and contribute to the support of the bladder
Anteriorly, the uterus is separated from the bladder by the vesicouterine pouch and from the rectum posteriorly by the rectouterine pouch or Douglas cul-de-sac. Laterally, the bilateral broad ligaments carry the neurovascular pedicles and their respective fascial coverings, attaching the uterus to the lateral pelvic sidewall.
The broad ligament is in contact inferiorly with the paravesical space, the obturator fossa, and the pelvic extension of the iliac fossa, to which it provides a peritoneal covering, and with the uterosacral ligament. Superiorly, it extends into the infundibulopelvic ligament.
Ureter
In its pelvic path in the retroperitoneum, several relationships are of significance and identify areas of greatest vulnerability to injury of the ureter (Fig. 5.25):
Figure 5.25 The course of the ureter and its relationship to the sites of greatest vulnerability.
1. The ovarian vessels cross over the ureter as it approaches the pelvic brim and lie in lateral proximity to the ureter as it enters the pelvis.
2. As the ureter descends into the pelvis, it runs within the broad ligament just lateral to the uterosacral ligament, separating the uterosacral ligament from the mesosalpinx, mesovarium, and ovarian fossa.
3. At about the level of the ischial spine, the ureter crosses under the uterine artery in its course through the cardinal ligament; the ureter divides this area into the supraureteric parametrium surrounding the uterine vessels and the infraureteric paracervix molded around the vaginal vessels and extending posteriorly into the uterosacral ligament. In this location, the ureter lies 2 to 3 cm lateral to the cervix and in proximity to the insertion of the uterosacral ligament at the cervix. This proximity warrants caution when using the uterosacral ligament for vaginal vault suspension (44,45).
4. The ureter then turns medially to cross the anterior upper vagina as it traverses the bladder wall.
About 75% of all iatrogenic injuries to the ureter result from gynecologic procedures, most commonly abdominal hysterectomy (46). Distortions of pelvic anatomy, including adnexal masses, endometriosis, other pelvic adhesive disease, or fibroids, may increase susceptibility to injury by displacement or alteration of usual anatomy. Careful identification of the course of the ureter before securing the infundibulopelvic ligament and uterine artery is the best protection against ureteric injury during hysterectomy or adnexectomy. Even with severe intraperitoneal disease, the ureter can always be identified using a retroperitoneal approach and noting fundamental landmarks and relationships.
Pelvic Floor
The pelvic floor includes all of the structures closing the pelvic outlet from the skin inferiorly to the peritoneum superiorly. It is commonly divided by the pelvic diaphragm into a pelvic and a perineal portion (47). The pelvic diaphragm is spread transversely in a hammocklike fashion across the true pelvis, with a central hiatus for the urethra, vagina, and rectum. Anatomically and physiologically, the pelvic diaphragm can be divided into two components: the internal and external components.
The external component originates from the arcus tendineus, extending from the pubic bone to the ischial spine. It gives rise to fibers of differing directions, including the pubococcygeus, the iliococcygeus, and the coccygeus.
The internal component originates from the pubic bone above and medial to the origin of the pubococcygeus and is smaller but thicker and stronger (47). Its fibers run in a sagittal direction and are divided into the following two portions:
1. Pubovaginalis fibers run in a perpendicular direction to the urethra, crossing the lateral vaginal wall at the junction of its lower one-third and upper two-thirds to insert into the perineal body. The intervening anterior interlevator space is covered by the urogenital diaphragm.
2. Puborectalis superior fibers sling around the rectum to the symphysis pubis; its inferior fibers insert into the lateral rectal wall between the internal and external sphincter.
The pelvic diaphragm is covered superiorly by fascia, which includes a parietal and a visceral component and is a continuation of the transversalis fascia (Fig. 5.26). The parietal fascia has areas of thickening (ligaments, septae) that provide reinforcement and fixation for the pelvic floor. The visceral (endopelvic) fascia extends medially to invest the pelvic viscera, resulting in a fascial covering to the bladder, vagina, uterus, and rectum. It becomes attenuated where the peritoneal covering is well defined and continues laterally with the pelvic cellular tissue and neurovascular pedicles.
Figure 5.26 The fascial components of the pelvic diaphragm.
Musculofascial elements (the hypogastric sheath) extend along the vessels originating from the internal iliac artery. Following these vessels to their respective organs, the hypogastric sheath extends perivascular investments that contribute to the formation of the endopelvic fascia so critical for the support of the pelvic organs.
Thus, the parietal fascia anchors the visceral fascia, which defines the relationship of the various viscera and provides them with significant fixation (uterosacral and cardinal ligaments), septation (vesicovaginal and rectovaginal), and definition of pelvic spaces (prevesical, vesicovaginal, rectovaginal, paravesical, pararectal, and retrorectal).
For its support, the pelvic floor relies on the complementary role of the pelvic diaphragm and its fascia resting on the perineal fibromuscular complex. It is composed of the perineal membrane (urogenital diaphragm) anteriorly and the perineal body joined to the anococcygeal raphe by the external anal sphincter posteriorly. This double-layered arrangement, when intact, provides optimal support for the pelvic organs and counterbalances the forces pushing them downward with gravity and with any increase in intra-abdominal pressure (Fig. 5.27). Dynamic imaging techniques, such as MRI, CT, and ultrasonography, increasingly are used to provide additional information in the evaluation of pelvic floor problems by visualizing anatomic landmarks during different functional phases.
Figure 5.27 The double-layered muscular support of the pelvic diaphragm.
Endopelvic Fascia
Controversy exists surrounding the use of the term “fascia” as it applies to the pelvis. Histologic studies reveal that the linings of the levator ani, piriformis, and obturator internus are genuine examples of pelvic fascia. One example in which the term “fascia” is incorrectly used is in reference to the tissue that is plicated in an anterior colporrhaphy. Histologically, it is the muscular lining of the vagina that is plicated. There are no discrete capsules of fascia that separate the bladder and vagina from each other.
The endopelvic fascia is a sheet of fibroareolar tissue following the blood supply to the visceral organs and acts as a retroperitoneal mesentery. The fascia divides the retroperitoneal space into avascular planes. The endopelvic or pubocervical fascia attaches the cervix and vagina to the lateral pelvic sidewall. It is composed of two parts: the parametrium, which is that part connected to the uterus (i.e., the uterosacral and cardinal ligaments), and the paracolpium, which is that part connected to the vagina. The parametrium and cardinal ligaments continue to the vaginal introitus and fuse directly to the supporting tissues associated with the vagina. The uterine and vaginal arteries travel in these structures. The uterosacral ligaments are the posterior components of the cardinal ligaments, extending from the cervix and upper vagina to the lateral sacrum. Lateral pelvic support is provided by linear condensations of obturator and levator ani fascia termed the arcus tendineus fascia pelvis and the arcus tendineus levator ani, respectively. The arcus tendineus levator ani serves as a point of attachment for the pubococcygeus and iliococcygeus muscles and lies on the fascia of the obturator internus muscle. It runs from the posterolateral pubic ramus to the ischial spine. The arcus tendineus fascia pelvis runs from the anterior pubis to the ischial spine as it joins with the arcus tendineus levator ani. It provides lateral (paravaginal) support to the anterior vagina.
Obturator Space
The obturator membrane is a fibrous sheath that spans the obturator foramen through which the obturator neurovascular bundle penetrates via the obturator canal. The obturator internus muscle lies on the superior (intrapelvic) side of the obturator membrane. The origin of the obturator internus is on the inferior margin of the superior pubic ramus and the pelvic surface of the obturator membrane. Its tendon passes through the lesser sciatic foramen to insert onto the greater trochanter of the femur to laterally rotate the thigh. The obturator artery and vein originate as branches of the internal iliac vessels. As they emerge from the cranial side of the obturator membrane via the obturator canal and enter the obturator space, they divide into many small branches, supplying blood to the muscles of the adductor compartment of the thigh. Cadaver work contradicted previous reports that the obturator vessels bifurcate into medial and lateral branches (48). Rather, the vessels are predominantly small (<5 mm in diameter) and splinter into variable courses. The muscles of the medial thigh and adductor compartment are (from superficial to deep) the gracilis, adductor longus, adductor brevis, adductor magnus, obturator externus, and obturator internus. In contrast to the vessels, the obturator nerve emerges from the obturator membrane and bifurcates into anterior and posterior divisions, traveling distally down the thigh to supply the muscles of the adductor compartment. With the patient in the dorsal lithotomy position, the nerves and vessels follow the thigh and course laterally away from the ischiopubic ramus. Transobturator incontinence slings and anterior trocar-based mesh prolapse kits are often placed beneath the adductor longus tendon and just lateral to the descending ischiopubic ramus in order to avoid the obturator neurovascular bundle, which lies lateral and superior to this relatively safe point of entry through the obturator membrane.
Summary
New surgical approaches are being developed to solve old problems and often require surgeons to revisit familiar anatomy from an unfamiliar perspective or with a different understanding of complex anatomic relationships. Examples of innovative surgical approaches that require renewed understanding of anatomic relationships include laparoscopic or robotic surgery, midurethral incontinence slings that traverse the obturator or retropubic spaces, and prolapse kits that traverse pararectal and paravesical spaces. Anatomic alterations secondary to disease, congenital variation, or intraoperative complications may make familiar surgical territory suddenly seem foreign. All of these situations require surgeons to be perpetual students of anatomy, regardless of their breadth or depth of experience.
Several strategies for continuing education in anatomy are suggested:
1. Review relevant anatomy before each surgical procedure.
2. Study the gynecologic literature on an ongoing basis—numerous publications document the evolution of newer concepts regarding anatomic issues such as pelvic support.
3. Operate with more experienced pelvic surgeons, particularly when incorporating new surgical procedures into practice.
4. Periodically dissect fresh or fixed cadaveric specimens; this practice may be arranged through local or regional anatomy boards or medical schools or by special arrangement at the time of autopsy.
5. Take advantage of newer computer-generated three-dimensional pelvic models and virtual reality interactive anatomic and surgical simulators, when available, to better understand functional anatomy and to help plan complicated surgical procedures (49,50).
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