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Abdominal and Pelvic Anatomy
Anatomy is to physiology as geography is to history; it describes the theater of events. Jean FranÇois Fernel
All gynecologic oncology surgeons should be familiar with the anatomy of the abdomen and pelvis to perform all complex and radical procedures required in the surgical management of women with gynecologic tumors. There has been an increasing emphasis on the role of upper abdominal surgery, particularly in the setting of advanced ovarian cancer. Therefore it is imperative that surgeons understand the detailed anatomy of the upper abdomen, in addition to the pelvic anatomy. A strong emphasis should be placed on the training of surgeons embarking on a career in gynecologic oncology to impart to them the skills and abilities to become proficient in surgery of the abdomen and pelvis. Gynecologic oncologists must understand the principles of multiple surgical disciplines, such as hepatobiliary surgery, urologic surgery, colorectal and intestinal surgery, and vascular surgery. The goal of this chapter is to provide surgeons with the anatomic details of the abdomen and pelvis. The material presented here aims to describe all structures relevant to the gynecologic oncologist.
Pelvic Anatomy
Pelvic anatomy remains the primary domain of the gynecologic surgeon. As a result, all who perform surgery in the pelvis should be thoroughly familiar with its intricate anatomic landmarks. The pelvic anatomy is complex and requires a great deal of expertise, given its detailed vascular and nerve structure, which demands the surgeon’s careful attention to the steps of the procedures. The consequences of severe complications, such as severe hemorrhage from vascular lacerations; fistulas of the urinary or gastrointestinal tract from injury to structures such as ureters, bladder, or bowel; and neuropathic injuries from lacerations or thermal injuries to nerves may all be potentially avoided by the surgeon’s devoting time to learning the complex anatomy of the pelvis ( Fig. 2.1 ).
Bony Pelvis
The bones that form the pelvis of the newborn are the ilium, ischium, pubis, sacrum, and coccyx. The ilium, ischium, and pubis join together at the age of 16 to 18 years to form a single bone, called the pelvic bone. Accordingly, in the adult, the bones of the pelvis comprise the right and left pelvic bones, the sacrum, and the coccyx ( Fig. 2.2 ). This bony pelvis is a firm structure to which all the pelvic ligaments and muscles are attached.
Ilium
The upper part of the pelvic bone is the ilium. Its superior aspect enlarges to form a flat wing that provides support for the muscles of the lower abdomen; it is also called the “false pelvis.” The medial surface of the ilium has two concavities forming the lateral borders of the pelvic channel. The superior and larger of these two concavities is the greater sciatic notch, and the ischial spine is its most prominent landmark.
Ischium
The ischium is the posterior and inferior part of the pelvic bone. The ischial spine marks the posterior margin of the bone.
Pubis
The anterior and inferior part of the pelvic bone is the pubis. The superior and inferior pubic branches are located anteriorly and articulate in the midline at the pubic symphysis.
Sacrum
The sacrum is composed of five sacral vertebrae that are fused together. Nerve outlets are positioned anterior and laterally; the sacral nerves run through them. The coccyx is attached inferiorly and is the posterior border of the pelvic outlet ( Fig. 2.3 ).
Orientation of the Bony Pelvis
Typically, surgeons operate with the pelvis in the horizontal position. However, in the erect woman the pelvis is naturally oriented so that the anterior superior iliac spine and the front edge of the pubic symphysis are in the same vertical plane, perpendicular to the ground. Therefore the pelvic inlet is tilted anteriorly, and the urogenital hiatus is parallel to the ground. This directs the pressure of the pelvic contents and forces them toward the pelvic bones instead of toward the muscular floor. Accordingly, in this position, the bony pelvis is oriented so that forces are distributed to diminish the stress on the pelvic musculature. In summary, most of the load of the abdominal and pelvic viscera is supported by this bony articulation inferiorly ( Fig. 2.4 ).
Anatomic Landmarks of the Bony Pelvis
The bones of the pelvis show some significant surgical landmarks that are important when the surgeon is operating inside the pelvis, including the ischial spine, coccyx, pubic arch, and pectineal line ( Fig. 2.5 ).
Ischial Spine
The ischial spine is a sharp protuberance on the inner surface of the ischium that separates the greater from the lesser sciatic notch. The ischial spine is important clinically and anatomically because it can be palpated easily via the vagina and rectum or throughout the retropubic space and serves as a point of fixation for many structures that are important for pelvic organ support. The arcus tendineus levator ani inserts posteriorly on the ischial spine. Also, the ischial spine represents the lateral attachment site of the sacrospinous ligament.
Coccyx
The coccyx is the terminal portion of the sacrum and consists of four joined coccygeal vertebrae. It is palpable through the vagina and the rectum and is a valuable landmark surgically for many pelvic interventions.
Pubic Arch
The two pubic bones form an arch beneath the pubic symphysis. The pubic arch serves as the upper and lateral borders of the urogenital triangle, under which the distal urethra and vagina exit. The mean pubic arch angle is 70 to 75 degrees; however, a wide variability can be seen.
Pectineal Line
The edge along the superior, medial surface of the superior pubic rami is denominated the pectineal line. Anteriorly, this line is continuous with the pubic crest. Overlying the pectineal line is the Cooper ligament.
Pelvic Ligaments
Two main ligaments connect the pelvic bones to the sacrum and coccyx: the sacrotuberous ligament and the sacrospinous ligament. These ligaments also convert the two indentations on the pelvic bones in two exit areas on the lateral pelvic walls: the greater and lesser sciatic foramina ( Fig. 2.6 ).
Sacrospinous Ligament
The sacrospinous ligament is a strong, triangular ligament; the high point of this ligament attaches to the ischial spine laterally, and the base joins to the distal sacrum and coccyx medially. This ligament divides the lateral pelvic outlet into two foramina: the greater sciatic foramen superiorly and the lesser sciatic foramen inferiorly. The coccygeus muscle is located on the superior surface of the sacrospinous ligament. The pudendal neurovascular package crosses behind the ischial spine and lateral aspect of the sacrospinous ligament as it exits the pelvis and enters the ischiorectal fossa. The S3 sacral nerve root and the pudendal nerve run over the superior margin of the sacrospinous ligament. The inferior gluteal artery, a branch of the posterior trunk of the internal iliac, is located close above the superior border of the sacrospinous ligament.
Sacrotuberous Ligament
The sacrotuberous ligament is also a triangular ligament. It has a broad base that extends from the posterior superior iliac spine along the lateral margin of the sacrum and coccyx. The apex of the ligament is attached to the medial margin of the ischial tuberosity. The sacrotuberous ligament forms the lateral-inferior border of the lesser sciatic foramen.
Pelvic Muscles
Muscles of the Lateral Pelvis
The obturator internus and piriformis are the muscles of the pelvic sidewalls.
Obturator Internus Muscle
The obturator internus muscle is found on the superior inner side of the obturator membrane. The obturator internus muscle originates from the inferior margin of the superior pubic ramus and from the pelvic surface of the obturator membrane. Its tendon exits the pelvis through the lesser sciatic foramen to insert onto the greater trochanter of the femur to laterally rotate the thigh. This muscle is innervated by the obturator internus nerve (L5–S2).
Piriformis Muscle
The piriformis muscle is part of the pelvic sidewall and is located posteriorly and lateral to the coccygeus muscle. It extends from the anterolateral sacrum to pass through the greater sciatic foramen and insert on the greater trochanter. Lying on top of the piriformis is a particularly large neurovascular plexus, the lumbosacral plexus.
Muscles of the Pelvic Floor
The skeletal muscles of the pelvic floor include the levator ani muscles and the coccygeus muscle. Both constitute the levator ani complex, called the levator platform when it is inserted in the midline.
Levator Ani Muscle Complex
The levator ani muscle complex is formed by several segments: the pubococcygeus, puborectalis, and iliococcygeus muscles. The urogenital hiatus is the space between the levator ani musculature through which the urethra, vagina, and rectum pass. Muscles of the pelvic floor, particularly the levator ani muscles, provide support to the pelvic visceral organs and play an integral role in urinary voiding, evacuation, and sexual function.
Arcus Tendineus Levator Ani
There is a linear thickening of the pelvic fascia covering the obturator internus muscle called the arcus tendineus levator ani. This thickened fascia forms a perceptible line from the ischial spine to the posterior surface of the superior pubic ramus in both sides. The muscles of the levator ani originate from this musculofascial attachment.
Puborectalis Muscle
The puborectalis muscle originates on the pubic bone, and its fibers pass posteriorly, forming a sling around the vagina, rectum, and perineal body. This results in the anorectal angle and promotes closure of the urogenital hiatus ( Figs. 2.7–2.12 ).
Avascular Spaces
Owing to its embryologic development, the pelvis comprises a number of avascular spaces and connective tissue planes that allow the different viscera to function independently. These spaces are limited by some of the visceral branches of both hypogastric arteries. Commonly they contain blood vessels and nerves and are filled with lax areolar tissue, allowing blunt and easy dissection without rupture of these structures ( Fig. 2.13 ).
The avascular spaces of the female pelvis include two lateral spaces (paravesical and pararectal) in both sides and four central spaces (space of Retzius or prevesical, vesicovaginal, rectovaginal, and presacral spaces) ( Fig. 2.14 ).
Retropubic Space (Space of Retzius)
The retropubic space, also called the space of Retzius, is a virtual space between the bladder and the pubic bone. The pubic bone, the peritoneum, and the muscles of the anterior abdominal wall limit it. Its lateral borders are the arcus tendineus and the ischial spines. Within the retropubic space appears the dorsal clitoral neurovascular bundle, located in the midline, and the obturator neurovascular pack, located laterally as it enters the obturator canal. In some women, an accessory obturator artery arises from the external iliac artery and runs along the pubic bone. The space lateral to the bladder neck and urethra contains some nerves innervating the bladder and urethra, as well as the venous plexus of Santorini, that results in excessive bleeding if the proper dissection is not performed. The dissection of this space must be a blunt dissection close to the pubic bone, avoiding the clitoral neurovascular bundle. The dissection is facilitated with a full bladder, which outlines its boundaries very clearly. The median umbilical ligament or urachus can then be grasped with downward traction and transected with monopolar cautery to enter the retropubic space ( Fig. 2.15 ).
Paravesical Spaces
The paravesical spaces are two lateral spaces that are localized anterior to the lateral parametria, lateral to the bladder, and lateral to the space of Retzius. Their margins are the superior vesical artery and bladder pillars medially; the external iliac vessels, obturator internus, and levator ani muscles laterally; the pubic bone anteriorly; and the lateral parametrium posteriorly. The paravesical space needs to be developed at the beginning for most pelvic radical procedures. Moreover, its dissection is indispensable to identify the anterior aspect of the lateral parametria or cardinal ligament. After transection of the round ligament, the surgeon develops this space softly between the superior vesical artery medially and the external iliac vessels laterally and medially displaces the lateral aspect of the bladder.
Pararectal Space
The pararectal spaces are bilaterally located posterior to the lateral parametria or cardinal ligaments. The cardinal ligament defines the borders of the pararectal space anteriorly; the space is defined medially by the rectum, posteriorly by the sacrum, and laterally by the internal iliac artery or pelvic sidewall. The pararectal space must always be developed at the time of radical hysterectomy and pelvic exenteration. Opening the broad ligament parallel and lateral to the infundibulopelvic ligament permits access to this space. The displacement of the uterus medially helps to expose the pararectal space. The ureter must be identified, and it usually remains attached to the peritoneum of the posterior leaf of the broad ligament. Then the space between the ureter and the internal iliac artery is developed with meticulous blunt dissection, avoiding bleeding of small vessels in this area that could delay the dissection ( Figs. 2.16 and 2.17 ).
Vesicovaginal Space
The vesicovaginal space is located in the midline. Its limits are the bladder anteriorly, the bladder pillars laterally, and the vagina posteriorly. The bladder pillars are composed of connective tissue and vessels, particularly small veins from the vesical plexus, and some cervical branches and contain the parametrial portion of the ureters. This plane is essential for the performance of any type of hysterectomy. To dissect the space, the surgeon should make a sharp incision in the midline between the bladder pillars; this incision will reveal a loose areolar avascular layer when in the proper plane. Misplacing the correct anatomic plane can result either in bleeding or in a bladder injury ( Fig. 2.18 ).
Rectovaginal Space
The rectovaginal space separates the posterior vaginal wall from the rectum. It starts at the pelvic cul-de-sac and extends to the perineal body. It contains lax areolar tissue that can easily be dissected. Its lateral margins are the rectal pillars, which are part of the cardinal-uterosacral ligament complex connecting the rectum to the sacrum. Frequently, the surgeon may need to enter the rectovaginal space during a hysterectomy when the patient has unrecognizable anatomic features owing to an obliterated cul-de-sac from endometriosis or malignant disease. In that case, both ureters should be identified in advance, followed by identification of the rectum, to prevent any injury ( Fig. 2.19 ).
Presacral Space
The presacral or retrorectal space is found between the rectum anteriorly and the sacrum posteriorly. This space is entered by dividing the peritoneum at the base of the mesentery of the sigmoid colon or through the pararectal spaces. Inferiorly this space terminates at the level of the levator muscles and laterally continues as the pararectal fossae. The middle sacral artery and a plexus of veins are attached superficial to the anterior longitudinal ligament of the sacrum. The endopelvic fascia in this space envelops the visceral nerves of the superior hypogastric plexus and lymphatic vessels. The lateral boundaries of the presacral space are formed by the common iliac arteries, both ureters, and the sigmoidal branches of the inferior mesenteric artery (IMA) crossing on the left side.
The correct plane of dissection is between the rectum and the presacral fascia. Adequate development of this plane allows a radical extirpation en bloc of the rectum with the entire mesorectum, critical in rectal cancer; a mistaken dissection from the natural plane, invading the presacral fascia, may lead to injury of presacral veins, leading to significant bleeding ( Fig. 2.20 ).
Uterine Support Structures
The structures that connect the cervix and vagina to the pelvic sidewall and sacrum are known as the cardinal and uterosacral ligaments, respectively or in conjunction, uterine parametria.
Parametria
The cardinal-uterosacral ligament complex suspends the uterus and upper vagina in their normal position. It serves to maintain vaginal length and keep the upper vaginal axis nearly horizontal in an erect woman so that the pelvic floor supports it. Absence of this support contributes to prolapse of the uterus and/or vaginal cuff. The cardinal ligaments are condensations of connective tissue that are several centimeters in width and run from the cervix and upper vagina to the pelvic sidewall. The uterine vessels run for much of their course within the cardinal ligaments.
The uterosacral ligaments are bands of connective tissue that are attached with the cardinal ligaments at their point of insertion in the cervix and upper vagina. The uterosacral ligaments pass posteriorly and inferiorly to attach to the ischial spine and sacrum.
The parametrium can be artificially divided into three bands of connective tissue: the posterior parametrium or uterosacral ligament, the cardinal ligament or lateral parametrium, and the cervicovesical ligament or anterior parametrium. The uterosacral ligaments are bands of connective tissue joining the cardinal ligaments at their point of insertion in the cervix. The uterosacral ligaments pass posteriorly and inferiorly to reach the ischial spine and sacrum. This ligament lies in close contact with the ureter before crossing the uterine artery within the lateral parametrium. The hypogastric nerve runs 1 to 2 cm inferior to the ureter and along the lateral aspect of the uterosacral ligament. The lateral parametrium contains the uterine artery and veins (superficial and deep) and some variable number of parametrial lymph nodes; in its deepest portion—close to the pelvic floor—appear the parasympathetic nerves (splanchnic nerves) coming from roots S2 to S4. Finally, the anterior parametrium, also known as the bladder pillar, includes the ureteric tunnel containing the ureter after crossing under the uterine artery ( Figs. 2.21–2.23 ).
Round Ligaments
The round ligaments are expansions of the uterine musculature. They originate at the uterine fundus anteriorly and inferiorly to the fallopian tubes, run retroperitoneally through the broad ligament, and then enter the inguinal canal, terminating in the labia majora.
Broad Ligament
The broad ligament covers the lateral uterine corpus and upper cervix. The limits of the broad ligament are as follows: superiorly, the round ligaments; posteriorly, the infundibulopelvic ligaments; and inferiorly, the cardinal and uterosacral ligaments. It consists of anterior and posterior leaves that separate to enclose viscera and blood vessels. Structures included within the broad ligament are considered retroperitoneal. Dissection between these sheets is necessary to provide retroperitoneal exposure of these structures. Various zones of the broad ligament are named for nearby structures such as the mesosalpinx (located near the fallopian tubes) and the mesovarium (located near the ovary). The broad ligament is composed of visceral and parietal peritoneum that contains smooth muscle and connective tissue.
Pelvic Vasculature
Arterial Supply
The aorta provides the blood supply to the pelvic structures. The aorta bifurcates at approximately the level of L4 to L5 into the right and left common iliac arteries. The common iliac arteries divide into the external iliac and internal iliac arteries; the internal iliac artery is also referred to as the hypogastric artery and provides most of the vascularization to the pelvic viscera and pelvic side wall and the gluteal muscles. The left common iliac vein travels anterior to the sacrum and medial to the aortic bifurcation and joins the right common iliac vein to form the vena cava under the right common iliac artery. The external iliac artery is located medial to the psoas muscle; it continues its course caudally to ultimately give off the femoral artery after crossing underneath the inguinal ligament. In the pelvis, the external iliac artery has few branches; these include the inferior epigastric artery and a variable superior vesical artery. The external iliac vein is much larger and lies posterior and medial to the artery. The external iliac vein also passes below the inguinal ligament before reaching the thigh.
The inferior epigastric vessels supply the rectus abdominis muscles. The inferior epigastric artery originates from the external iliac artery and travels through the transversalis fascia into a space between the rectus muscle and posterior sheath. In their course from the lateral position of the external iliac vessels, the inferior epigastric artery and vein run obliquely toward a more medial location as they approach the umbilicus. The superficial epigastric vessels originate from the femoral artery, perfuse the anterior abdominal wall, and branch extensively as they approach the umbilicus.
The hypogastric artery branches into anterior and posterior divisions. The posterior division runs toward the large sciatic notch, dividing into the lateral sacral, iliolumbar, and superior gluteal arteries. The anterior division of the internal iliac artery branches into the obliterated umbilical, uterine, superior vesical, obturator, vaginal, and inferior gluteal and internal pudendal arteries. The internal iliac vein lies medial to the internal iliac artery; the other veins travel with their corresponding arteries ( Figs. 2.24–2.26 ).
To reach the perineum, the internal pudendal artery courses through the greater sciatic foramen, around the sacrospinous ligament, and back in through the lesser sciatic foramen. In this way the pudendal artery ends up below the pelvic diaphragm. Its branches supply the anal sphincter, the pelvic diaphragm, and the external genital structures in the female.
The internal iliac artery is a retroperitoneal structure; for any of its branches to be identified and accessed, a retroperitoneal dissection must be performed. The ureter should be identified before ligation of any lateral pelvic vessel. Most of the blood supply to the uterus, tubes, and ovaries derives from the uterine and ovarian arteries. The uterine arteries originate from the anterior division of the internal iliac arteries in the retroperitoneum. They usually share a common origin with the obliterated umbilical artery or superior vesical artery. The obliterated umbilical arteries, also known as superior vesical arteries and as lateral umbilical ligaments, are a useful landmark for the identification of the uterine artery. Simply pulling up the obliterated umbilical artery permits easy identification of the uterine artery. The uterine artery travels through the cardinal ligament over the ureter and approximately 1.5 cm lateral to the cervix. It then joins the uterus near the level of the internal cervical os, branching upward and downward toward the uterine corpus and inferiorly toward the cervix. The uterine corpus branches anastomose with vessels that derive from the ovarian arteries, thus providing collateral blood flow. The uterine artery also sends a branch to the cervicovaginal confluence at the lateral aspect of the vagina. The vagina also receives its blood supply from this uterine branch, as well as from a vaginal branch of the internal iliac artery, which anastomoses along the lateral wall of the vagina. The ovarian arteries arise from the abdominal aorta. The right ovarian vein drains to the inferior vena cava (IVC), whereas the left ovarian vein drains to the left renal vein. The ovarian vessels travel through the infundibulopelvic ligaments in proximity to the ureter, along the medial aspect of the psoas muscle.
The ureter is supplied by small branches of the blood vessels it crosses: the common iliac, internal iliac, and superior and inferior vesical arteries. Above the pelvic brim the blood supply enters from the medial side; below the pelvic brim the blood supply to the ureter enters laterally. The blood supply to the bladder includes the superior and inferior vesical arteries, which are branches of the anterior trunk of the internal iliac artery. The blood supply to the rectum and anus consists of an anastomotic arcade of vessels from the superior rectal branch of the IMA and the middle and inferior rectal branches of the internal pudendal artery (see Figs. 2.24–2.26 ).
Venous Drainage
The IVC receives the venous flow from the right and common iliac veins and is located to the right of the aortic bifurcation. Similar to the arterial correspondents, the external iliac vein primarily drains the lower limbs, whereas the internal iliac vein drains the pelvic viscera, walls, gluteal region, and perineum. In most instances the major veins are mirror images of their arterial counterparts. However, the smaller vessels can vary from one individual to another. The inferior epigastric, deep circumflex iliac, and pubic veins are all pelvic tributaries of the external iliac vein. The external iliac vein is the upper continuation of the femoral vein. The nomenclature of the vessel changes at the mid-inguinal point, posterior to the inguinal ligament. The deep circumflex iliac vein crosses the anterior surface of the external iliac artery before entering the external iliac vein. Inferior to the entry point of the deep circumflex iliac vein, the inferior epigastric vein enters the external iliac vein cephalad to the inguinal ligament. The pubic vein forms a bridge between the obturator vein and the external iliac vein. On the left side, the external iliac vein is always medial to its corresponding artery. However, on the right side, it starts out in a medial position and gradually becomes posterior, as it gets closer to the point of fusion.
The internal iliac vein receives the middle rectal, obturator, lateral sacral, inferior gluteal, and superior gluteal veins as tributaries. The obturator vein enters the pelvis by way of the obturator foramen, where it takes a posterosuperior route along the lateral pelvic wall, deep to its artery. In some instances the vessel is replaced by an enlarged pubic vein, which then joins the external iliac vein. The superior and inferior gluteal veins are accompanying veins of their corresponding arteries. The tributaries of the superior gluteal veins are named after the branches of the corresponding artery. They pass above piriformis and enter the pelvis via the greater sciatic foramen before joining the internal iliac vein as a single branch. The inferior gluteal veins form anastomoses with the first perforating vein and medial circumflex femoral vein before entering the pelvis via the greater sciatic foramen. The middle rectal vein is a product of the rectal venous plexus that drains the mesorectum and the rectum. It also receives tributaries from the bladder, as well as gender-specific tributaries from the prostate and seminal vesicle or the posterior wall of the vagina. It terminates in the internal iliac vein after travelling along the pelvic part of levator ani. Finally, the lateral sacral veins travel with their arteries before entering the internal iliac vein.
The internal and external iliac veins unite at the sacroiliac joint, on the right side of the fifth lumbar vertebra, to form the common iliac vein. The right common iliac vein is almost vertical and shorter than the left common iliac vein, which takes a more oblique course. The right obturator nerve crosses the right common iliac vein posteriorly; the sigmoid mesocolon and superior rectal vessels cross the left common iliac vein anteriorly. The internal pudendal vein drains to the internal iliac vein, whereas the median sacral veins drain into the common iliac vessels directly. The median sacral veins unite into a single vessel before entering the left common iliac vein. The internal pudendal veins receive inferior rectal veins and either clitoral and labial or penile bulb and scrotal veins before joining the common iliac vein ( Figs. 2.27 and 2.28 ).
Pelvic Lymphatic System
The lymphatic drainage of the pelvis follows the vessels. The lymph nodes are located under the peritoneum adjacent to the pelvic vasculature. The main groups of pelvic lymph nodes include the common iliac, external iliac, internal iliac, obturator, and presacral nodes. The presacral nodes, also known as medial sacral lymph nodes, run along the middle sacral artery in the presacral space. The common iliac nodal group consists of three subgroups: lateral, middle, and medial. The lateral subgroup is an extension of the lateral chain of external iliac nodes located lateral to the common iliac artery. The medial subgroup occupies the triangular area bordered by both common iliac arteries from the aortic bifurcation to the bifurcation of the common iliac artery into the external and internal iliac arteries. Nodes at the sacral promontory are included in this chain. The middle subgroup is located in the lumbosacral fossa and between the common iliac artery and common iliac vein.
The external iliac lymph nodes are located lateral to the external iliac artery and medial to the external iliac vein. They receive their lymphatic flow from the legs via the inguinal nodes and also from the pelvic viscera. The external iliac nodal group consists of three subgroups: lateral, middle, and medial. The lateral subgroup includes nodes that are located along the lateral aspect of the external iliac artery. The middle subgroup comprises nodes located between the external iliac artery and the external iliac vein. The medial subgroup contains nodes located medial and posterior to the external iliac vein. The medial subgroups are also known as the obturator nodes. The obturator lymph nodes are located in the obturator fossa, medial to the external iliac vessels and lateral to the obliterated umbilical ligament. The obturator nodes can be located by identifying the obturator nerve, which is usually the most easily visualized component of the obturator neurovascular bundle as it enters the obturator canal.
The internal iliac nodal group, also known as the hypogastric nodal group, consists of several nodal chains accompanying each of the visceral branches of the internal iliac artery. Among the nodes of this group, the connecting nodes are located at the junction between the internal and external iliac nodal groups. The internal iliac lymph nodes are located along the internal iliac vessels and are most numerous in the lateral pelvic side walls. In addition to the lymphatic drainage from the pelvic viscera, these nodes drain the pelvic viscera, the lower urinary tract, and gluteal region.
The uterine lymphatic flow also drains to the superficial inguinal lymph nodes along the round ligament, as well as to the presacral nodes along the uterosacral ligaments. Metastasis of uterine and cervical malignancies may occur in the superficial inguinal lymph nodes, as well as to the external and iliac nodes, and presacral nodes. The lymphatic drainage of the uterus and the upper two-thirds of the vagina flows through the obturator and internal and external iliac lymph nodes and ultimately drains into the common iliac lymph nodes. The lymphatic drainage of the ovaries travels with the ovarian vessels to the paraaortic lymph nodes. The distal one-third of the vagina, urethra, and vulvar lymphatic drainage goes to the inguinal nodes, reflecting their distinctly different embryologic origin compared with the upper genital tract.
Finally, the inguinal nodes appear outside the pelvis. This group consists of superficial inguinal and deep inguinal nodes. The superficial inguinal nodes, which are located in the subcutaneous tissue anterior to the inguinal ligament, accompany the superficial femoral vein and the saphenous vein. The sentinel nodes for the superficial subgroup are those situated at the saphenofemoral junction, where the great saphenous vein drains into the common femoral vein. The deep inguinal nodes are those located along the common femoral vessels under the cribriform fascia. The anatomic landmarks that mark the boundary between the deep inguinal nodes and the medial chain of the external iliac nodes are the inguinal ligament and the origins of the inferior epigastric and circumflex iliac vessels ( Fig. 2.29 ).
Pelvic Nerves ( Fig. 2.30 )
Somatic Nerves
Nerves crossing the pelvis are derived from the lumbar (T12–L5) and sacral plexuses (L4–S4) ( Figs. 2.31 and 2.32 ). The lumbar and sacral plexuses are formed from the lumbar and sacral nerve roots, lateral to the intervertebral foramina. The lumbar plexus lies within the psoas muscle and forms the iliohypogastric and ilioinguinal nerves, the lateral cutaneous nerve of the thigh, and the genitofemoral nerve. They provide sensation to the inguinal region, mons pubis, upper vulva, and anterior upper thigh. The lumbar plexus has two major nerves of the lower extremity: the femoral and the obturator nerves ( Figs. 2.33 and 2.34 ). The former emerges laterally to the psoas major, and the latter emerges medial to it. The femoral nerve runs alongside the psoas major and passes beneath the inguinal ligament, just lateral to the femoral artery. The femoral nerve is the major branch of the lumbar plexus, supplying sensory and motor function to the thigh. The obturator nerve runs just below the pelvic brim and enters the obturator canal.
The sacral plexus lies on the sacrum and piriformis muscle. It is formed by the anterior rami of sacral roots S1 to S4. In addition, it receives a contribution from L4 and L5, through the lumbosacral trunk ( Fig. 2.35 ). The major branch of the sacral plexus, the sciatic nerve (L4–S3) ( Fig. 2.36 ), exits the pelvis through the inferior portion of the greater sciatic foramen to innervate the muscles of the hip, pelvic diaphragm, vulva, perianal area, and lower leg. Almost all nerves arising from the sacral plexus go to the lower extremity. A main nerve of the sacral plexus is the pudendal nerve (S2–S4), which is the principal nerve of the vulva; it also involves the small motor nerves to the pelvic diaphragm. It arises from S2 to S4 just above the sacrospinous ligament and passes lateral to the ischial spine to reenter the pelvis through the greater foramen. Then it travels forward along the Alcock canal attached to the obturator internus muscle. Its branches supply the anal sphincter, the muscles of the urogenital diaphragm, and the external genitalia. A small branch or branches from S3 or S4 supply most of the levator ani muscle and the coccygeus muscle ( Fig. 2.37 ).
Autonomic Nerves
The autonomic nerve supply to the pelvis runs through the superior hypogastric plexus, a ganglionic plexus that lies over the bifurcation of the aorta in the presacral space ( Fig. 2.38 ). The superior hypogastric plexus receives sympathetic input from the thoracic and lumbar splanchnic nerves and afferent pain input from the pelvic viscera ( Fig. 2.39 ). Parasympathetic input, sometimes called the nervi erigentes, derives from S2 to S4 via the pelvic splanchnic nerves, which travel to join the hypogastric plexuses through the lateral pelvic wall, crossing the lateral parametrium in its deepest portion. From the superior hypogastric plexus, the splanchnic nerves split into two hypogastric nerves that run along the internal iliac vessels. These nerves connect to the inferior hypogastric plexus ( Fig. 2.40 ). The inferior hypogastric plexus is located lateral to the pelvic viscera and consists of three areas: the vesical plexus, uterovaginal plexus, and middle rectal plexus. All these nerves, sympathetic and parasympathetic, are connected to a diffuse and extensive plexus of autonomic nerves called the pelvic plexus. The pelvic plexus lies within the fascia that covers this part of the pelvic wall and floor ( Fig. 2.41 ).
Pelvic Viscera
Female Upper Genital Tract
The female upper genital tract consists of the cervix, uterine corpus, fallopian tubes, and ovaries. The uterus includes the corpus and cervix. In women of reproductive age, the corpus is twice the size of the cervix, whereas in prepubertal and postmenopausal woman they are of similar sizes. However, the dimension of the uterus may vary significantly depending on hormonal status, previous pregnancies, or the presence of uterine pathology. The corpus, or body, of the uterus has a triangular shape. The upper portion is called the fundus, and the inferior portion that is continuous with the cervix is named the isthmus, or lower uterine segment. There are no anatomic landmarks that divide these portions from the rest of the uterine corpus. The uterus is made up of three layers. The endometrium is the inner lining of the uterine cavity, with a superficial layer that consists of glandular epithelium and stroma. The thickness of the endometrium changes with the menstrual cycle or any other hormonal stimulation. The myometrium is the thickest layer of the uterus. It is composed of smooth muscle fibers that are oriented in different directions. Finally, the serosa is the thin external lining layer of the uterus, investing the body of the uterus, consisting of the visceral peritoneum. The cervix is a cylindrical structure that acts as the conduit between the endometrial cavity and the vagina. The superior portion is continuous with the uterus. During hysterectomy, the junction between the uterine corpus and cervix can be located by palpating the area to feel the superior border of the cervix, which is tubular and firmer compared with the uterus. The inferior portion of the cervix projects into the vagina. In some women, because of special circumstances the cervix may appear flat with the vagina on examination rather than prominent. The cervical canal opens into the endometrial cavity at the internal orifice and into the vagina at the external os. The ectocervix is the surface of the cervix that can be visualized from the vagina. The cervix contains fibrous connective tissue mixed with smooth muscle located on the periphery that forms a continuous layer between the myometrium and the muscle in the vaginal wall. The endocervical canal is covered with glandular epithelium. This transforms into stratified squamous epithelium on the ectocervix owing to exposure to the acidic environment that is present in the vagina after menarche. The area where the epithelium changes from glandular to squamous is known as the transformation zone and is the area of the cervix that is most predisposed to dysplasia and malignant transformation.
The uterine adnexa consist of the ovaries and fallopian tubes. The ovaries are attached to the uterus laterally and/or posteriorly, depending on the position of the patient. The connecting structures of the ovaries include the utero-ovarian ligament, which attaches the ovary to the uterus; the infundibulopelvic ligament, which contains the ovarian vessels and joins the ovary to the retroperitoneum; and the part of the broad ligament that forms the mesovarium. The ovary consists of an external cortex, where the oocytes and follicles are located, and the central stroma, where the blood vessels and connective tissue create a fibromuscular tissue layer. The fallopian tubes arise from the uterine corpus posterior and superior to the round ligaments. The broad ligaments support the tubes with a progressive thickening of connective tissue called the mesosalpinx. Frequently, paratubal cysts appear within the mesosalpinx; these are fragments of the embryologic ducts that form and then disappear during embryologic development. The fallopian tube connects the uterine and abdominal cavities. Each tube is divided into four different portions: the interstitial portion, where the tube passes through the uterine cornua; the isthmus, with a narrow lumen and thick muscular wall; the ampulla, with a larger lumen and mucosal folds; and finally the fimbria, located at the end of the tube, with leaflike protrusions that increase the surface area on the distal part of the tubes to facilitate interaction with the oocyte. The fallopian tubes consist of an outer muscularis layer of the tube with longitudinal smooth muscle fibers and an inner layer with circular fibers. The fallopian tube mucosa is composed of numerous delicate papillae consisting of three cell types: ciliated columnar cells; nonciliated columnar secretory cells; and intercalated cells, which may simply represent inactive secretory cells.
Bladder
The bladder is located in the midline of the pelvis, just posterior to the pubic bone. The bladder is separated from the pubic bone by a virtual plane, called the retropubic space or the space of Retzius, which contains the venous plexus of Santorini. The borders of the bladder include the pubic symphysis anteriorly, the pelvic side walls on both sides, and the lower uterine segment and vagina posteriorly. The inferior boundary of the bladder is the lower uterine segment and anterior cervix. The superior border of the bladder is in contact with the obliterated umbilical arteries laterally and in the midline with the urachus. In the fetus, the urachus connects the developing bladder to the umbilicus. After delivery the urachus becomes the median umbilical ligament, which joins the apex of the bladder to the anterior abdominal wall. The upper part of the bladder is covered by the parietal peritoneum of the anterior abdominal wall. Inferiorly, the peritoneum reaches the vesicouterine fold. The rest of the bladder is located retroperitoneally. The bladder is very distensible. When empty, the bladder orients the apex toward the pubic bone. When full, the bladder is globular, with normal capacities ranging from 400 to 500 mL. When the bladder is expanded, the musculature of the dome can become thin. Consequently, before a pelvic surgical procedure is initiated, decompression of the bladder with a bladder catheter can help avoid injury. The regions of the bladder include the dome superiorly and the base inferiorly. The base of the bladder lies directly on the anterior vaginal wall and consists of the trigone and detrusor loop, a thickening of the detrusor muscle, the thickness of which does not vary with filling of the bladder. The bladder trigone is a triangular area at the base of the bladder bounded by the internal urethral meatus and the two ureteric orifices. The ureteric orifices and the internal urethral meatus form a triangle of 3 cm per side.
Histologically, three layers line the bladder: mucosa, muscle, and adventitia. The bladder mucosa consists of a transitional cell epithelium and underlying lamina propria and is also known as the urothelium. The muscular layer, or the detrusor muscle, consists of interlacing bundles of smooth muscle. This plexiform organization of detrusor muscle bundles is ideally suited to reduce all dimensions of the bladder lumen on contraction. The outer adventitial layer primarily consists of adipose tissue and loose connective tissue. The blood supply to the bladder includes the superior and inferior vesical arteries, which are branches of the anterior trunk of the internal iliac artery. Bladder innervation is provided by the parasympathetic and sympathetic autonomic fibers of the pelvic and hypogastric nerve plexuses, respectively.
Ureters
The ureters are retroperitoneal structures that run from the renal pelvis to the bladder. They are approximately 25 to 30 cm in length from the renal pelvis to the trigone of the bladder. The pelvic brim divides them into abdominal and pelvic segments, each of which is approximately 12 to 15 cm in length ( Fig. 2.42 ). The pelvic ureters can be injured during pelvic surgery. The ureters enter the pelvis at the pelvic brim, where they cross from lateral to medial, as well as anterior to the bifurcation of the common iliac arteries The ureters enter the pelvis very close to the ovarian vessels; therefore identification of the ureter is imperative before an adnexectomy is performed. The ureter usually lies first medial and deeper to the infundibulopelvic ligament, so typically it may be necessary to open the retroperitoneal space lateral to the infundibulopelvic ligament and create a window between the ovarian vessels and the ureter to safely secure the ovarian vascular pedicle. The ureters then descend into the pelvis within a peritoneal cover attached to the medial leaf of the uterine broad ligament and the lateral pelvic side wall. At the level of the uterus, the ureter descends along the lateral side of the uterosacral ligament. It then passes under the uterine arteries, entering the ureteric tunnel and crossing the anterior parametrium in the upper portion of the vagina. The ureters enter the posterior aspect of the bladder and run obliquely through the bladder wall for 1.5 cm before terminating in the trigone ( Fig. 2.43 ). The ureter is supplied by the blood vessels it crosses—the ovarian, internal iliac, superior vesical, and inferior vesical arteries. Above the pelvic brim the blood supply enters from the medial side; below the pelvic brim, the blood supply enters laterally.
Sigmoid Colon, Rectum, and Anus
The sigmoid colon enters the pelvis from the descending colon slightly to the left of the midline and is basically an extraperitoneal organ. Its blood supply derives from the sigmoid arteries, branches of the IMA. Once the sigmoid colon has descended into the pelvis, its course straightens. It enters the retroperitoneum at the pelvic posterior cul-de-sac and becomes the rectum. Then it gets wider, forming the rectal ampulla, an area of final storage, and turns downward to almost a 90-degree angle to become the anus. The rectum and anus rest on the sacrum and levator ani muscles, and the vagina lies anterior to the rectum, separated from it by the rectovaginal septum. The blood supply to the rectum and anus consists of an anastomotic arcade of vessels from the superior hemorrhoidal branch of the IMA, and the middle and inferior hemorrhoidal branches of the internal and pudendal artery, respectively. The anus is surrounded by the internal anal sphincter and external anal sphincter. The internal anal sphincter consists of a thicker layer of the circular involuntary smooth muscle fibers, which provides 80% of the latent tone of the sphincter. The external anal sphincter consists of skeletal muscle fibers and is attached to the coccyx ( Fig. 2.44 ).
Perineum
The area localized between the vagina and anus is typically referred to as the perineum; nevertheless, from the strictly anatomic point of view, the perineum is the anatomic territory that includes the pelvic outlet inferior to the pelvic floor. The area between the vagina and anus is more properly called the perineal body. The limits of the anatomic female perineum are the ischiopubic rami, ischial tuberosities, sacrotuberous ligaments, and coccyx. A virtual line linking the ischial tuberosities divides the perineum into the urogenital triangle above and the anal triangle below. It is remarkable that in the standing position the urogenital triangle is oriented horizontally and the anal triangle is inclined upward so that it faces more posteriorly.
Perineal Membrane
The perineal membrane is a dense fibrotic layer situated over the urogenital triangle. Laterally, it is inserted in the pubic arch and has a free posterior margin anchored in the midline by the perineal body. The urethra and vagina cross throughout the urogenital hiatus in the perineal membrane to exit at the introitus. The perineal membrane, therefore, offers the anatomic support of the distal urethra, distal vagina, and perineal body to be connected to the lateral pubic arches.
Urogenital Triangle
The urogenital triangle is divided into a superficial and a deep perineal area. The superficial perineal space contains the superficial perineal muscles including the ischiocavernosus and the superficial transverse perineal muscles, the erectile tissue of the clitoris, the vestibular bulbs, and the Bartholin glands. The deep perineal space lies just beneath the perineal membrane and inferior to the levator ani muscles. Within the deep perineal space lie the external urethral sphincter and the urethrovaginalis, and the deep transverse perineal muscles ( Fig. 2.45 ).
Perineal Body
The perineal body is the point of junction of the superficial and deep transverse perineal muscles, perineal membrane, external anal sphincter, posterior vaginal muscularis, and fibers from the puborectalis and pubococcygeus muscles. The perineal body plays an important role in support of the vagina and in normal anal function. The pudendal neurovascular trunk provides the vascular and nerve supply to the perineum, including the deep and superficial perineal spaces.
Anal Triangle
The anal triangle is formed on both sides by the internal margins of the sacrotuberous ligaments, anteriorly by the superior edge of the perineal membrane and perineal body, and inferiorly by the coccyx. The superior roof of the anal triangle is the levator ani muscle. The anal canal and anal sphincter muscles are situated in the middle of the anal triangle. Lateral to the anal sphincter complex on each side is the ischiorectal fossa.
Ischiorectal Fossa
The ischiorectal fossa is the space under the levator ani muscles and over to the perineum. This fossa is occupied primarily with fatty tissue, surrounding the anus and urogenital hiatus. The lateral wall of each fossa is formed by the ischium, obturator internus muscle, and sacrotuberous ligament. The medial wall is the levator ani muscle. Crossing the lateral margin of the ischiorectal fossa is the pudendal canal. Also called the Alcock canal, it contains the internal pudendal artery, the internal pudendal veins, and the pudendal nerve ( Fig. 2.46 ).
Vulva
The female external genitalia or vulva includes the labia majora, labia minora, clitoris, vulvar vestibule, external urethral meatus, and vaginal orifice. The labia minora split anteriorly to form medial and lateral folds. The lateral folds join superiorly over the clitoris to form the clitoral hood. The labia minora blend posterior to the vestibule to form the posterior fourchette. The labia majora are lateral to the labia minora and unite anteriorly to form the mons pubis. The mons pubis is a fat pad that overlies the inferior aspect of the pubic symphysis. The vulvar vestibule is the area encircled by the labia minora into which the urethra and vagina exit in the perineum. The hymen is a ring-shaped membrane that surrounds the vaginal orifice and typically has one or more central perforations. Within the vestibule, the outlets of the Skene glands appear on each side of the lateral margin of the urethra. Similarly, the exits of the Bartholin glands are found on the posterior lateral margin of the vagina, distal to the hymen insertion ( Figs. 2.47–2.49 ).
Vagina
The vagina is a fibromuscular cylindrical cavity with a great distensile capacity; it is covered with rugal mucosal folds that extend from the vestibule to the uterine cervix. The longitudinal shape of the vagina resembles a trapezoid, narrowest at the introitus and becoming progressively wider as it approaches the vaginal apex and cervix. In the transverse plane, the vagina has a boxlike configuration at its distal end (toward the introitus) and is flattened proximally. In the sagittal plane, the vagina has a distinct angulation. The upper two-thirds of the vagina angles toward the third and fourth sacral vertebrae and is almost horizontal in the erect woman. The lower one-third is almost vertical as it crosses through the perineal membrane to the vestibule.
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