Surgical Anatomy and Instrumentation




SURGICAL ANATOMY



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The complexities of radical extirpative surgery for locally advanced and recurrent pelvic cancer and the associated procedures necessary for successful functional and cosmetic reconstruction require a thorough understanding of anatomy that extends from the upper abdomen to the thigh. This chapter is not intended as an exhaustive anatomic discourse but rather as a summary of the relevant anatomic considerations important to the various operative procedures detailed in the chapters that follow.



Pelvis



1. Pelvic viscera


The true pelvis is bounded by the pelvic floor inferiorly and the pelvic brim superiorly and is defined by an imaginary line connecting the sacral promontory, the upper margin of the pubic symphysis, and the arcuate and pectineal lines (Figure 2-1). The pelvis contains the urinary bladder, rectosigmoid colon, uterus, adnexa, and a portion of the vagina, and important vasculature and lymphatic structures. The uterus is a centrally located organ between the bladder anteriorly and the rectosigmoid colon posteriorly. The muscular upper portion of the uterus is the fundus, while the tapered more fibrous component is the cervix, which directly communicates with the vagina. The fallopian tubes arise from the lateral, superior portion of the uterine corpus anterior to the utero-ovarian ligaments. The utero-ovarian ligaments suspend the ovaries and contain anastomoses between the uterine and ovarian vessels. The adnexa are classically lateral to the uterus; however, they may be found between the uterus and the rectosigmoid colon along the pelvic sidewall.




Fig. 2-1.


Pelvis lateral view, right paramedian section.





The only portion of the uterus not covered with serosa is the anterior cervix, which is covered by the bladder. The posterior portion of the bladder not only covers the anterior cervix, but it also overlies the proximal vagina. The anterior portion of the bladder lies against the pubic symphysis and abdominal wall, and the lateral and inferior portions lie against the obturator internus and levator ani muscles, respectively. The ureters are smooth muscle, retroperitoneal structures that drain urine from the kidney and enter the pelvis at the level of the bifurcation of the common iliac artery, medial to the infundibulopelvic ligament. They cross the common iliac vessels anteriorly and course laterally, under the infundibulopelvic ligaments while descending into the pelvis, running posterior to the ovary and deep to the broad ligament before traversing through the cardinal ligament and under the uterine artery approximately 2 cm lateral to the cervix. The ureters then curve anteromedially to enter the back of the bladder at the vesicoureteric junction.



The sigmoid colon is a short “S” curving of the descending colon just before the rectum. It is normally approximately 40 cm in length and is distinguished from the descending colon and rectum because it features a traditional mesentery and is not retroperitoneal. The sigmoid mesocolon fixes the sigmoid loop at the junction between the iliac colon and rectum; however, it can have a considerable range of motion. The sigmoid colon gradually transitions to the rectum just cephalad to the level of the posterior pelvic cul-de-sac, also known as the peritoneal reflection, and is defined by both a loss of appendices epiploicae and attenuation of the taenia coli. The posterior cul-de-sac, or pouch of Douglas, is formed by the posterior cervical and proximal vaginal peritoneum and the rectal peritoneum. The rectum is approximately 12 cm long, terminates at the anorectal ring, and transitions to the anal canal, which signifies the end of the gastrointestinal tract. The proximal one-third of the rectum is covered by peritoneum along the anterior and lateral portions. The middle third of the rectum is covered anteriorly by peritoneum, and the distal one-third is entirely retroperitoneal.



2. Ligaments and potential spaces


The term ligament, when used in the pelvis, refers to one of several membranous peritoneal folds that support the visceral organs and can contain vasculature, nerves, and smooth muscle. Five paired ligaments suspend the uterus. The round ligaments are extension of the uterine muscle that extend from the anterior fundus to the pelvic retroperitoneum lateral to the epigastric vessel and pass into each inguinal canal, where they continue to the labia majora and mix with the tissue of the mons pubis. The artery of Sampson runs in the round ligament. The broad ligaments are large folds of peritoneum that connect the lateral aspect of the uterus to the pelvic sidewalls and floor. The paired cardinal (Mackenrodt’s) ligaments are located at the base of the broad ligament and attach the cervix to the pelvic sidewall (Figure 2-2). Each cardinal ligament contains the uterine, inferior vesicle, vaginal, middle rectal arteries and veins, and associated lymphatics. The posterior portion of cardinal ligament also contains major components of the autonomic nerve supply to the bladder and rectum. The uterosacral ligaments arise from the inferior portion of the posterior uterus and attach to the front of the sacrum, “sandwiching” the rectum at the rectal pillars. The ovaries are suspended to the uterus by the utero-ovarian ligaments and to the pelvic sidewall by the infundibulopelvic ligaments, which contain the respective gonadal artery and vein.




Fig. 2-2.


Potential spaces and ligaments of the pelvis.





There are 8 potential spaces (2 paired lateral spaces and 4 unpaired midline spaces) in the pelvis that are filled with fatty or areolar tissue and that are important in radical pelvic surgery, as they provide relatively bloodless cleavage planes during dissection (see Figure 2-2). The retropubic space of Retzius is bounded anteriorly by the pubic symphysis and posteriorly by the bladder. Laterally, it merges with the paired paravesical spaces, with the point of delineation being the umbilical artery. The paravesical space is typically developed by first dividing the round ligament and extending the peritoneal incision superiorly, inferiorly, and parallel to the infundibulopelvic ligament. The paravesical space is then entered between the superior vesicle artery or umbilical artery and the external iliac vein. The boundaries of each paravesical space are the pubic symphysis anteriorly, the superior vesicle artery and umbilical artery medially, the obturator internus muscle and external iliac vein laterally, and the cardinal ligament posteriorly. The cardinal ligament is the demarcation between the paravesical spaces and the paired pararectal spaces. The boundaries of each pararectal space include the cardinal ligament anteriorly, the rectum medially, the internal iliac artery laterally, and the sacrum posteriorly. The pararectal spaces merge posteriorly with the retrorectal or presacral space. The retrorectal space is defined by the posterior rectal fascia anteriorly, the pararectal spaces laterally, and Waldeyer’s fascia along the anterior sacrum posteriorly. The rectovaginal space is bounded by the vagina anteriorly, the uterosacral ligaments laterally, and the rectum posteriorly. Lastly, the vesicouterine space continues inferiorly as the vesicovaginal space is defined by the posterior portion of the bladder anteriorly, the vesicouterine ligaments (bladder pillars) laterally, and the cervix (proximal) and vagina (distal) posteriorly.



3. Vascular anatomy and lymphatic drainage


The primary blood supply to the pelvis and lower extremities comes from the common iliac arteries, which arise from the bifurcation of the aorta at the level of L4 to L5 and extend laterally, where they divide across the sacroiliac joints to form the external and internal (hypogastric) iliac arteries (Figure 2-3). Each external iliac artery gives rise to an inferior epigastric artery, immediately proximal to the inguinal ligament, before it crosses under the ligament and becomes the femoral artery, which supplies the lower extremity. The inferior epigastric artery occasionally arises from the femoral artery and it supplies the lower portion of the rectus abdominis muscle and anastomoses with the superior epigastric artery, which arises from the internal thoracic artery. Preservation of the inferior epigastric artery is required for use of the rectus abdominis muscle for myocutaneous flap reconstructive surgery. The external iliac artery also gives rise to the deep circumflex artery at the level of the inferior epigastric artery. The deep circumflex iliac artery ascends obliquely behind the inguinal ligament to the anterior superior iliac spine, where it anastomoses with a branch of the lateral femoral circumflex artery.




Fig. 2-3.


Pelvic vasculature.





The external iliac veins enter the pelvis inferior to the corresponding arteries; however, the right common iliac vein lies lateral to the right common iliac artery, while on the left side this relationship is reversed. In a small percentage of cases (22%), an accessory obturator vein enters the external iliac vein near its midpoint, which can be prone to tearing during dissection of the overlying obturator lymph nodes.



Each internal iliac (hypogastric) artery bifurcates into anterior and posterior divisions approximately 4 to 5 cm distal to the common iliac bifurcation. The posterior division typically gives rise to 3 parietal arteries: the iliolumbar, lateral sacral (superior and inferior branch), and the superior gluteal arteries. The anterior division of the internal iliac artery gives rise to 3 parietal and 3 or 4 visceral arteries. The visceral branches are the umbilical, uterine, and middle rectal arteries; a separate vaginal artery may also be present. The umbilical artery gives rise to the superior and inferior vesicle arteries before traversing toward the umbilicus and becoming obliterated. The parietal branches of the anterior division of the internal iliac artery are the obturator, internal pudendal, and inferior gluteal arteries. The venous drainage of the internal iliac system is variable and typically forms a large plexus deep within the lateral pelvis.



The major blood supply to the uterus is via the uterine artery, which gives off an inferior vaginal branch and an ascending branch that anastomoses superiorly with a descending branch of the ovarian artery. The ovarian arteries are unique in that they arise as paired visceral branches from the anterolateral surface of the aorta 2 to 3 cm below the renal arteries. The ovarian venous system does not mirror its arterial partner. The left ovarian vein enters the left renal vein lateral to the aorta, whereas the right ovarian vein enters the anterolateral portion of the vena cava just inferior to the renal vein.



The blood supply to the bladder originates at the umbilical artery, which gives rise to the superior and inferior vesicle arteries. The venous drainage of the bladder does not follow the arterial supply, instead draining the bladder neck through a large plexus of veins, which also forms anastomoses with the dorsal vein of the clitoris and vaginal plexus veins. Venous drainage continues from the bladder neck through the bladder pillars and into the cardinal ligament. The blood supply to the ureter comes from multiple small branches that arise along its path from the abdomen to the deep pelvis and have multiple anastomoses in the ureteral adventitia. The vascular supply to the abdominal ureter consists of branches to its medial aspect arising from the aorta, common iliac artery, and ovarian vessels, whereas the pelvic ureter receives its blood supply along its lateral aspect via branches from the internal iliac, uterine, and vesicle arteries.



The blood supply to the upper vagina comes from descending branches of the uterine arteries. A separate vaginal artery can arise directly from the anterior division of the internal iliac artery or from the pudendal artery. The lower portion of the vagina is supplied by the inferior rectal artery or the inferior pudendal artery.



The rectum receives vascular supply from multiple sources including the inferior rectal artery (a branch of the internal pudendal artery), the middle rectal artery, the median sacral artery, and the superior rectal artery, which is a branch of the inferior mesenteric artery (IMA; Figure 2-4). The middle sacral artery arises from the posterior aspect of the aorta just above the aortic bifurcation and also gives off lateral sacral arteries. The critical point of Sudeck is represented by the bifurcation of the IMA into the superior rectal artery and the lowest sigmoid artery and has the potential for poor perfusion states if used for surgical anastomosis in the presence of hypotension.




Fig. 2-4.


Vascular supply to the rectum. Multiple anastomoses between the inferior mesenteric artery and internal iliac arterial systems, along with the middle sacral artery, to supply the rectum.





The lymphatic drainage of the pelvic viscera can follow multiple routes, depending on the primary site of origin. Lymphatic drainage from the ovaries, fallopian tubes, and uterine fundus usually follow the ovarian veins directly to the abdominal aorta lymphatics (para-aortic, para-caval, and aorto-caval lymph nodes). The proximal vagina, cervix, lower uterine segment, and occasionally, the uterine fundus typically drain through the lymphatics of the broad ligament to the pelvic lymph node group, which is composed of the obturator, internal iliac, and external iliac nodal chains. Jackson’s node refers to the distal-most external iliac lymph node. There is a separate lymphatic drainage pathway via the round ligament to the external iliac and inguinofemoral lymph nodes. The pelvic lymph node group drains to the common iliac lymph nodes and then to the aortic and caval node chains.



Vulva, Groin, and Anterior Thigh



Topographically, the vulva consists of the mons pubis, the paired labia majora and labia minora, clitoris, urethra, vaginal introitus, paired Bartholin’s glands, paired paraurethral (Skene’s) glands, the perineum, anus, and perianal tissue (Figure 2-5). Underlying the labia majora are the labial fat pads, which cover the superficial perineal compartment. The superficial perineal compartment contains the crura of the clitoris, the vestibular bulbs, and 3 paired muscles. The bulbocavernosus muscle immediately lies laterally to the lower vaginal wall, while the ischiocavernosus muscle runs along the medial margin of the pubic ramus (Figure 2-6). The perineal membrane is a tough connective tissue structure that traverses these 2 muscles. The ischiocavernosus muscles cover the clitoral crura and attach to the inferior pubic rami. The bulbocavernosus muscles cover the vestibular bulbs and run from the perineal body to the clitoris, passing around the vaginal introitus and urethral meatus. The superficial transverse perineal muscles run from the anterior ischial tuberosities to attach to the central tendon of the perineum. Cephalad to the superficial perineal space is the deep perineal space, which contains the deep transverse perineal muscle, and is delineated by the inferior and superior fascia of the urogenital diaphragm. The superior surface of the urogenital diaphragm is contiguous with the inferior surface of the levator ani muscle. The levator ani muscle (iliococcygeus, pubococcygeus, and puborectalis muscles) arises from the inner surface of the lesser pelvis and unites with its contralateral component in the midline, fusing with the bulbocavernosus and external anal sphincter muscles, to form the majority of the floor of the pelvic cavity (Figure 2-7). In combination with the coccygeus muscle, the levator ani muscle forms the pelvic diaphragm.




Fig. 2-5.


Topographic anatomy of the vulva.






Fig. 2-6.


Vascular and deep muscular anatomy of the vulva.






Fig. 2-7.


Musculature of the pelvic floor.





The vulva has 2 main sources of vascular support. The pudendal artery arises from the internal iliac (hypogastric) artery, which reaches the vulva via the pudendal (Alcock’s) canal, and gives off the inferior rectal artery (within the ischiorectal fossa) and the perineal artery (see Figure 2-6). As it traverses the vulva superiorly, the internal pudendal artery becomes the clitoral artery. The second major blood supply to the vulva arises from the common femoral arteries, which give rise to the superficial external pudendal arteries (supplying the anterior and medial vulva) and the deep external pudendal arteries (supplying the labia majora and labial fat pads). The venous drainage of the vulva generally follows the arterial system except for the superficial and deep external pudendal veins, which drain into the greater saphenous vein rather than the femoral vein.

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Jan 12, 2019 | Posted by in GYNECOLOGY | Comments Off on Surgical Anatomy and Instrumentation
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