General Anatomy

Anatomically, the retroperitoneum is not sharply defined. In principle, it includes the peritoneum-covered anatomic structures that constitute the posterior wall of the abdominal cavity and the pelvic space and are thus located dorsal to the abdominal cavity. Depending on the definition, the wall of the pelvic basin, well known to the gynecologic surgeon, may also be designated as retroperitoneal. Commentary on these retroperitoneal portions of the pelvis is found in the anatomic presentation of the pelvic spaces (Chapter 5, Uterus). They are only briefly presented here, together with a description of the course of important nerve structures.

The retroperitoneum of the posterior wall of the abdomen, cranial to the common and external iliac vessels, is usually reserved for the gynecologic oncologist. Although this retroperitoneal space seems like a closed book to the beginner, the anatomy of the zone is actually easily understandable. The surgeon encounters it especially in the context of para-aortic and paracaval lymphadenectomy. Its lateral boundary is the frame created by the colon (ascending colon on the right side, descending colon on the left). Whereas the ascending and descending large intestine are secondarily retroperitoneal, the transverse colon is located intraperitoneally. Cranially, the easily accessible portion of the retroperitoneal space can be extended by simply pushing aside the duodenum as far as the renal veins that usually form the most cranial border of the lymphadenectomy.

Retroperitoneum Nerves

The pelvic retroperitoneal space is traversed by the internal iliac vessels and their terminal branches, the lateral umbilical ligament, the superior vesical artery, the uterine artery and vein, the obturator vessels and the accompanying obturator nerve, and naturally by the ureter. Deep in the pelvic retroperitoneal space and not normally encountered by the gynecologic surgeon lie the branches of the sacral plexus (L5–S3), from which the superior and inferior gluteal nerves, the posterior cutaneous femoral nerve, the sciatic nerve, and the pudendal nerve arise.

The components of the autonomic nervous system, difficult to see intraoperatively, are functionally important. Emerging from the celiac plexus, nerve filaments run caudally along the anterolateral walls of the aorta, picking up fibers from the inferior mesenteric ganglion and the lumbar sympathetic trunk. At the bifurcation of the aorta, these filaments unite into the superior hypogastric plexus, also known as the presacral nerve, that lies on the sacral promontory, directly under the peritoneum. This divides into two nerve strands (right and left hypogastric branches) that run medial to the internal iliac vessels deep into the inferior hypogastric plexus. In addition to receiving preaortic visceral (sympathetic) fibers, the superior hypogastric plexus is supplied by the lumbar splanchnic nerves (parasympathetic system).

The inferior hypogastric plexus is thus supplied with sympathetic fibers via the right and left hypogastric branches from the sacral sympathetic trunk, T11–L2, and with parasympathetic fibers via the delicate nerve filaments of the pelvic splanchnic nerves, S2–S4. It supplies the autonomic innervation of the pelvic organs over its distribution network, also known as the pelvic plexus. The inferior hypogastric plexus lies deep in the pelvis bilaterally, medial to the internal iliac vessels. It is often described as lying directly on the levator plate. Nerve fibers of the inferior hypogastric plexus lead anterolaterally to the intestine as the pelvic plexus and from inferolateral and laterodorsal to the bladder and the internal genitalia. These terminal branches, accompanying the visceral branches of the internal iliac artery, reach the organs of the pelvis where they form nerve networks, also called the rectal plexus, uterovaginal plexus, and vesical plexus.

The nerve strands of the hypogastric branch/nerve associated with the inferior hypogastric plexus (running in the sacrouterine ligament) and of the splanchnic nerves (running in the cardinal ligament) are at particular risk when these ligaments are transected in a radical hysterectomy.

Retroperitoneal Space Vessels

The dominant vascular structures are the inferior vena cava and the aorta and—after their respective bifurcation—the common iliac arteries and the right and left common iliac veins. Major branches of these principal vessels are, from the bifurcation upward, the inferior mesenteric artery, which usually branches 5–7 cm above the bifurcation of the aorta, directly from its anterior wall, usually offset 2–3 mm to the left. (The inferior mesenteric vein runs back to the portal vein, and therefore the vena cava has no corresponding branch here.) The inferior mesenteric artery is usually spared by the gynecologic surgeon, but if necessary, and usually without negative consequences, it can be transected even when a deep intestinal anastomosis in the pelvis after partial sigmoid/rectum resection is planned. Further cranial to the branching of the inferior mesenteric artery, the two ovarian arteries branch directly from the anterior wall of the aorta at a sharp angle in a lateral caudal direction, attach themselves to the ovarian veins and thus pass caudally in the infundibulopelvic ligament to the adnexa. The ovarian arteries are rather delicate structures anatomically that are often only noticed during dissection and can then be easily coagulated. In contrast, the ovarian veins are more voluminous and easily seen, especially when they are ligated caudally; they must be distinguished from the ureter. The right ovarian vein runs to the anterior side of the inferior vena cava while the left vein usually leads to the left renal vein. This junction usually forms the cranial and left lateral border of complete para-aortic and paracaval lymphadenectomy. The small perforator veins from the inferior vena cava, running directly into the precaval lymphatic and fat tissue, are very important in dissection even though extremely delicate. If tension is placed on them, they can tear off during precaval lymphadenectomy and lead to direct, small hemorrhages from the vena cava that can only be coagulated with difficulty and therefore must sometimes be carefully sutured. Careful stepwise dissection of the precaval lymphatic and fat tissue with constant coagulation of even the finest vessels prevents these hemorrhages. The number of these perforators decreases significantly from caudal to cranial. The lumbar arteries and veins that branch dorsolaterally from the inferior vena cava and the abdominal aorta are important vessels at the most dorsal border of the surgically accessible retroperitoneum; they can be damaged in very aggressive lymphadenectomy or removal of clinically affected lymph nodes, for example, in the interaortocaval space.

Retroperitoneal Space Course of the Ureter

The most important structure for the gynecologic surgeon in the retroperitoneal space is the ureter. It must be exposed to view along its course in hysterectomy, lymphadenectomy, removal of the infundibulopelvic ligament, and mobilization of sigmoid and cecum. The total length of the ureter is between 25 and 30 cm. This length is divided by the edge of the pelvis into 12–15 cm abdominal and pelvic segments.

Abdominal segment. The abdominal segment of the ureter runs anterior to the psoas muscle and posterior to the ovarian vessels. The right ureter runs laterally to the inferior vena cava and crosses the common iliac artery to the right at the level of its division into external and internal iliac arteries. The left ureter runs lateral to the aorta, and posterior to the inferior mesenteric artery, the ovarian vessels, and the descending colon. At the left brim of the pelvis, because of the course of the sigmoid but in particular because of the physiologic peritoneal adhesions between the sigmoid and left infundibulopelvic ligament and the left wall of the pelvis, the ureter is often only visible after release of these structures as the first step in ureterolysis.

Pelvic section. In the pelvis itself, the ureters run close to the medial peritoneal lamina, posterior to the ovarian vessels, and continue to medially, toward the cervix, under the uterine arteries that extend into the uterus, and into the parametrium. Usually the distance from the internal cervical aperture laterally to the ureter is given as about 2 cm. From here, the ureter runs in a dense connective tissue sheath, also known as the “Wertheim tunnel,” that consists of the fibrous tissue of the cardinal ligament. Immediately after it crosses under the uterine artery, the ureter again approaches the cervix in an anterocaudal direction, in the so-called ureteral knee. Here it is particularly difficult to dissect the uterus free in a radical hysterectomy. The remaining path runs even more sharply medially and slightly anterocaudal, where the ureter enters the vesical trigone lying on the vagina, somewhat anterior to the vaginal fornix.