ANATOMY

There is no greater aid to surgical expertise than an intimate knowledge of anatomy. For the urologist, the areas of greatest importance are the retroperitoneum and pelvis. In this chapter, retroperitoneal structures important to the practice of urologic surgery are described in detail and clinical correlations are provided where helpful.

THE RETROPERITONEUM ( Fig. 1-1 )

The retroperitoneum is bounded posteriorly by the abdominal wall, which consists of the lumbodorsal fascia and the enclosed sacrospinalis and quadratus lumborum muscles. Laterally, the retroperitoneum is contiguous with the preperitoneal fat and is bounded laterally by the transversus abdominis musculature of the lateral abdominal wall. The peritoneum is the anterior limit while cranially the diaphragm ( Fig. 1-2 ) limits the retroperitoneum. Caudally the retroperitoneum is contiguous with the extraperitoneal pelvic structures.

Figure 1-1 A, The retroperitoneum dissected. The anterior perirenal (Gerota's) fascia has been removed. B, 1, Diaphragm. 2, Inferior vena cava. 3, Right adrenal gland. 4, Upper pointer, celiac artery; lower pointer, celiac autonomic nervous plexus. 5, Right kidney. 6, Right renal vein. 7, Gerota's fascia. 8, Pararenal retroperitoneal fat. 9, Perinephric fat. 10, Upper pointer, right gonadal vein; lower pointer, right gonadal artery. 11, Lumbar lymph nodes. 12, Retroperitoneal fat. 13, Right common iliac artery. 14, Right ureter. 15, Sigmoid colon (cut). 16, Esophagus (cut). 17, Right crus of diaphragm. 18, Left inferior phrenic artery. 19, Upper pointer, left adrenal gland; lower pointer, left adrenal vein. 20, Upper pointer, superior mesenteric artery; lower pointer, left renal artery. 21, Left kidney. 22, Upper pointer, left renal vein; lower pointer, left gonadal vein. 23, Aorta. 24, Perinephric fat. 25, Aortic autonomic nervous plexus. 26, Upper pointer, Gerota's fascia; lower pointer, inferior mesenteric ganglion. 27, Inferior mesenteric artery. 28, Aortic bifurcation into common iliac arteries. 29, Left gonadal artery and vein. 30, Left ureter. 31, Psoas major muscle covered by psoas sheath. 32, Cut edge of peritoneum. 33, Pelvic cavity. C, The retroperitoneum dissected. The kidneys and adrenal glands have been sectioned, and the inferior vena cava has been excised over most of its intra-abdominal course. D, 1, Inferior vena cava (cut). 2, Diaphragm. 3, Right inferior phrenic artery. 4, Right adrenal gland. 5, Upper pointer, celiac artery; lower pointer, superior mesenteric artery. 6, Right kidney. 7, Upper pointer, right renal artery; lower pointer, right renal vein (cut). 8, Lumbar lymph node. 9, Transversus abdominis muscle covered with transversalis fascia. 10, Right ureter. 11, Anterior spinous ligament. 12, Inferior vena cava (cut). 13, Right common iliac artery. 14, Sigmoid colon (cut). 15, Right external iliac artery. 16, Esophagus (cut). 17, Left adrenal gland. 18, Celiac ganglion. 19, Left kidney. 20, Upper pointer, left renal artery; lower pointer, left renal vein (cut). 21, Left renal pelvis. 22, Aorta. 23, Aortic autonomic nervous plexus. 24, Inferior mesenteric ganglion. 25, Left ureter. 26, Inferior mesenteric artery. 27, Psoas major muscle covered by psoas sheath. (A to D, Reproduced from the Bassett anatomic collection, with permission granted by Dr. Robert A. Chase.)

Figure 1-2 The diaphragm: abdominal surface. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 317.)

Posterior Abdominal Wall Posterior Musculature and Lumbodorsal Fascia (Figs. 1-3 to 1-6 [3] [4] [5] [6], Table 1-1 )

The lumbodorsal fascia surrounds the sacrospinalis and quadratus lumborum, which together comprise the posterior abdominal wall. The lumbodorsal fascia originates from the spinous processes of the lumbar vertebrae and extends anteriorly and cranially. As it progresses upward, it separates into three layers: posterior, middle, and anterior.

Figure 1-3 Posterior abdominal wall musculature, superficial dissection. A section of the latissimus dorsi muscle has been removed. The location of the right kidney within the retroperitoneum is shown by dashed outline.

Figure 1-4 Posterior abdominal wall musculature, intermediate dissection. The sacrospinalis muscle and three anterolateral flank muscle layers are seen in cut section, and the three layers of the lumbodorsal fascia posteriorly can be appreciated.

Figure 1-5 Posterior abdominal wall musculature, deep dissection. The lumbodorsal fascia and costovertebral ligament are visualized, arising from the transverse processes of the lumbar vertebrae. The relation of the kidney and pleura is also shown.

Figure 1-6 Muscles of the posterior abdominal wall. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 316.)

Table 1-1 -- Musculature of the Posterior and Lateral Abdominal Wall

Muscle	Origin	Insertion	Function
Sacrospinalis	Sacrum and lumbar vertebrae	Lower ribs and thoracic vertebrae	Extension of the spine
Quadratus lumborum	5th lumbar vertebra	1st through 4th lumbar vertebrae, 12th rib	Depress and stabilize 12th rib, lateral bending of the trunk
External oblique	Lower eight ribs	Lateral lip of iliac crest, aponeurosis ending in midline raphe	Compress abdominal contents, flexion of the trunk
Internal oblique	Lumbodorsal fascia, iliac crest	Lower four ribs, aponeurosis ending in linea alba	Compress abdominal contents, flexion of the trunk
Transversus abdominis	Lumbodorsal fascia, medial lip of iliac crest	Aponeurosis ending in linea alba	Compress abdominal contents
Psoas	12th thoracic through 5th lumbar vertebrae	Lesser trochanter of femur	Flexion of the hip
Iliacus	Inner aspect of iliac pelvic wing	Lesser trochanter of femur	Flexion of the hip

Adapted from Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, pp 250 and 316.

KEY POINTS: GENETICS AND DEVELOPMENT

▪ The three layers of the lumbodorsal fascia cover the musculature of the posterior abdominal wall. ▪ The lower ribs are in intimate contact with the kidneys and adrenal glands. Injury to the lower ribs suggests injury to retroperitoneal structures. ▪ The renal artery lies posterior to the renal vein, but this relationship is reversed when the aorta and inferior vena cava divide into the common iliac vessels. Here, the common iliac arteries are anterior to the common iliac veins. ▪ As lymphatic drainage moves within the retroperitoneum from caudal to cranial there is also a predominantly right-to-left flow. ▪ The nervous system is divided into the autonomic and somatic systems. ▪ The autonomic system is further divided into sympathetic and parasympathetic innervation. The sympathetics originate from the thoracic and lumbar vertebrae. From the sympathetic chain ganglia preganglionic fibers proceed to autonomic plexuses. From these plexuses postganglionic sympathetic fibers proceed to their targets. The parasympathetics originate from the cranial and sacral vertebrae and again synapse in peripheral plexuses before proceeding to their targets. ▪ The somatic system provides innervation to the retroperitoneum and lower extremities via the lumbosacral plexus.

The posterior layer provides the posterior covering for the sacrospinalis muscle as well as the origin for the latissimus dorsi muscle. The middle layer forms the fascial layer separating the anterior aspect of the sacrospinalis muscle from the posterior aspect of the quadratus lumborum. The anterior layer of the lumbodorsal fascia provides the anterior covering to the quadratus lumborum muscle and forms the posterior margin of the retroperitoneum. As one moves laterally away from the sacrospinalis and quadratus lumborum muscles, the lumbodorsal fascial layers fuse together and then connect with the transversus abdominis muscle.

The quadratus lumborum and sacrospinalis muscles (Figs. 1-6 and 1-7 [6] [7]) form the muscular portion of the posterior abdominal wall filling the space between the 12th rib, spine, and iliac crest. The quadratus lumborum serves a number of functions. It supports the 12th rib, thus improving diaphragmatic contraction and inspiration as well as aiding intercostal muscle function during forced expiration. Finally, it controls lateral bending of the trunk. The sacrospinalis also controls movement of the trunk by promoting extension of the spine. These muscular and fascial relationships become important clinically when performing a dorsal lumbotomy incision. As seen in Figure 1-7 , this is a vertical incision lateral to the border of the sacrospinalis and quadratus lumborum. This approach allows entrance to the retroperitoneum without the violation of the musculature.

Figure 1-7 Transverse section through the kidney and posterior abdominal wall showing the lumbodorsal fascia incised. Note that through such a lumbodorsal incision the kidney can be reached without incising muscle. (After Kelly and Burnam, from McVay C: Anson & McVay Surgical Anatomy, 6th ed. Philadelphia, WB Saunders, 1984.)

Lateral Flank Musculature ( Fig. 1-8 ; see Table 1-1 )

Three muscular layers comprise the lateral flank musculature. From superficial to internal, these are the external oblique, internal oblique, and transversus abdominis muscles. The most superficial structure is the external oblique muscle. This muscle arises from the lower ribs and moves from lateral to medial as it progresses caudally. Final attachment is to the iliac crest caudally and the rectus sheath anteriorly. The posterior border remains free as it terminates before reaching the lumbodorsal fascia. Next is the internal oblique muscle. Again, this muscle arises from the lower rib cage, but the orientation of the fibers is from medial to lateral as they move caudally. Final attachment is to the iliac crest and lumbodorsal fascia. The final structures are the transversus abdominis muscle and transversalis fascia. This muscle arises from the lumbodorsal fascia with fibers running directly transversely until it attaches anteriorly and medially onto the rectus sheath. Immediately deep to the transversus abdominis muscle is the transversalis fascia and then the retroperitoneal space. The function of the lateral flank musculature is to compress and stabilize the abdomen and trunk. This provides controlled movement as well as protection for the abdominal organs.

Figure 1-8 Transverse section showing layers of the lateral flank musculature. (From Drake RL, VoGL W, Mitchell AWM: Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 252.)

Psoas and Iliacus Muscles (see Fig. 1-6 )

The psoas major muscle originates on the 12th thoracic through the 5th lumbar vertebrae. A smaller psoas minor is identifiable in about one half of the population and resides medial to the psoas major. The psoas muscle(s) is covered by the psoas fascia. In close proximity to the psoas muscle is the iliacus muscle, which attaches to the inner aspect of the iliac pelvic wing. As the iliacus progresses caudally it joins with the psoas muscle to form the iliopsoas muscle. This combined muscle then joins to the lesser trochanter of the femur and controls flexion of the hip.

Lower Rib Cage ( Fig. 1-9 )

In addition to the protection provided by the muscular layers of the posterior and lateral abdominal wall, the 10th, 11th, and 12th ribs safeguard the upper retroperitoneal space and are intimately related to the adrenal glands and kidneys. Given the close proximity, injury to these ribs can be associated with significant retroperitoneal injury. While providing protection, the lower ribs and the accompanying pleura and lung limit surgical exposure to the upper retroperitoneum. The limits of the pleura are the 8th rib anteriorly, the 10th rib in the midaxillary line, and the 12th rib posteriorly. Given this location of the pleura, flank incisions at or above the 11th or 12th ribs risk pleural violation.

Great Vessels

The abdominal aorta and inferior vena cava are the great vessels of the abdomen, providing vascular supply to the abdominal organs and lower extremities (Figs. 1-10 and 1-11 [10] [11]).

Figure 1-11 Cross-sectional anatomy of the upper abdomen at the level of the kidneys demonstrated with transverse sections obtained by computed tomography. Sections are arranged from most cephalic to caudal. A, Section through the upper poles of the kidneys, superior to the renal vascular pedicles. B, Section through the level of the renal arteries and veins. C, Slightly more inferior section showing the renal pelves and relation of the duodenum to the right renal hilum. D, Section through the lower poles of the kidneys showing the upper ureters. Ao, aorta; DUO, duodenum; GB, gallbladder; IVC, inferior vena cava; LK, left kidney; PANC, pancreas; PNF, perinephric fat; RA, renal artery; RK, right kidney; RP, renal pelvis; RV, renal vein; SMA, superior mesenteric artery; SMV, superior mesenteric vein; U, ureter.

Figure 1-10 Inferior vena cava and abdominal aorta and their branches.

Abdominal Aorta

The aorta enters the abdomen via the aortic hiatus found between the diaphragmatic crura in the posterior diaphragm at the level of the 12th thoracic vertebrae (see Fig. 1-2 ). It continues caudally to the 4th lumbar vertebrae where it bifurcates into the common iliac arteries. During its course through the abdomen the aorta gives off a number of large branches ( Table 1-2 ). The paired inferior phrenic arteries are first. They supply the inferior diaphragm and the superior portion of the adrenal gland (see Fig. 1-2 ). Next is the celiac trunk, which is the origin for the common hepatic, left gastric, and splenic arteries that supply the liver, stomach, and spleen, respectively. The paired adrenal arteries follow with an artery going to each adrenal gland.

Table 1-2 -- Branches of the Abdominal Aorta

Artery	Branch	Origin	Parts Supplied
Celiac trunk	Anterior	Immediately inferior to aortic hiatus of diaphragm	Abdominal foregut
Superior mesenteric artery	Anterior	Immediately inferior to celiac trunk	Abdominal midgut
Inferior mesenteric artery	Anterior	Inferior to renal arteries	Abdominal hindgut
Middle adrenal arteries	Lateral	Immediately superior to renal arteries	Adrenal glands
Renal arteries	Lateral	Immediately inferior to superior mesenteric artery	Kidneys
Testicular or ovarian arteries	Paired anterior	Inferior to renal arteries	Testes in male and ovaries in female
Inferior phrenic arteries	Paired	Immediately inferior to aortic hiatus	Diaphragm
Lumbar arteries	Posterior	Usually four pairs	Posterior abdominal wall and spinal cord
Median sacral arteries	Posterior	Just superior to aortic bifurcation, pass inferiorly across lumbar vertebrae, sacrum, and coccyx
Common iliac arteries	Terminal	Bifurcation usually occurs at the level of L4 vertebra

From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 331.

The superior mesenteric artery leaves the aorta on the anterior side and supplies the entire small intestine and majority of the large intestine. Also of note, this artery communicates with the celiac trunk vasculature via the pancreaticoduodenal artery. Overlying the 2nd lumbar vertebrae, the paired renal arteries are the next branching point of the aorta. To the urologist, renal artery anatomy is obviously of great importance and is discussed in detail in the kidney section.

Moving distally on the aorta, the paired gonadal arteries are encountered. In the male this artery is also called the testicular artery and in the female it is the ovarian artery. The initial course in both the male and female is similar, with the artery moving caudally and laterally from the aorta, with the right gonadal artery crossing anterior to the inferior vena cava. In men, the gonadal artery then crosses over the ureter and exits the retroperitoneum at the internal inguinal ring. In women the course is different: instead of exiting the pelvis the artery crosses medially back over the external iliac vessels and enters the pelvis. It then proceeds via the suspensory ligament to the ovary. The destination of the gonadal artery (the testis in the male and the ovary in the female) has significant collateral sources of arterial blood, from the deferential and cremasteric arteries in the male and the uterine artery in the female. Thus the gonadal artery can generally be ligated during retroperitoneal surgery without detrimental effect.

After the gonadal arteries, the inferior mesenteric artery is found on the anterior side of the aorta before its bifurcation into the common iliac vessels. This vessel provides vascular supply to the left third of the transverse colon, descending colon, sigmoid colon, and rectum. In patients without significant vascular disease, this artery can be sacrificed without ill effect because there is collateral circulation to these bowel segments from the superior mesenteric, middle hemorrhoidal, and inferior hemorrhoidal arteries.

In addition to the listed arteries that exit the aorta from its anterior or lateral aspect, there are a number of small branches from the posterior side of the aorta. Lumbar arterial branches are found at regular intervals along the length of the aorta, with generally four pairs located within the retroperitoneum. These branches supply the posterior body wall and spine. Again these arteries can generally be ligated without detrimental effects, although spinal ischemia and paralysis has occurred after ligation at multiple levels. The final posterior branch from the aorta is the middle sacral artery, which exits the aorta immediately before the branching of the common iliac arteries and then sends branches to the rectum and anterior sacrum. The common iliac arteries then proceed into the pelvis, thus completing the arterial course through the retroperitoneum.

The Inferior Vena Cava

The inferior vena cava (IVC) arises from the confluence of the common iliac veins at the level of the 5th lumbar vertebra (see Fig. 1-10 ). Because the common iliac veins lie medial and posterior to the iliac arteries, the confluence of the iliac veins is posterior and to the right of the aortic bifurcation. As the IVC progresses cranially through the abdomen, tributaries include the gonadal, renal, adrenal, and hepatic veins. In addition, the middle sacral vein enters the inferior vena cava posteriorly and the lumbar veins enter throughout the length of the abdominal vena cava.

The first tributary encountered along the IVC is the middle sacral vein, which enters at the junction of the common iliac veins. Also entering along the posterior aspect of the IVC throughout its course are lumbar veins. These veins course anterior to the spinal transverse processes and generally parallel the lumber arteries. In addition to providing vascular drainage, the lumbar veins connect the IVC to the azygous venous system on the right side and hemiazygous venous system on the left side of the thorax. This provides alternate routes of venous drainage within the retroperitoneum ( Fig. 1-12 ).

Figure 1-12 Lumbar, azygos, and hemiazygos veins. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 332.)

The next tributaries to the IVC are the gonadal veins, whose course is analogous to the gonadal arteries until approaching the IVC. During the cranial portion of their course these veins are more lateral and closer to the ipsilateral ureter. Of surgical importance is their terminal drainage because the right gonadal vein drains directly into the IVC and the left empties into the inferior aspect of the left renal vein (see Fig. 1-10 ).

After the gonadal veins, the renal veins are encountered. The renal veins are generally directly anterior to the accompanying renal artery, but it is not unusual for them to be separated by 1 to 2 cm in the craniocaudal direction. The right renal vein typically is short and without branches, but in a small minority of patients the right gonadal vein can enter the right renal vein as opposed to the IVC. In a second anatomic variation, a lumbar vein will enter on the posterior aspect of the right renal vein as opposed to entering the IVC directly. The left renal vein is significantly longer than the right and receives additional branches before entering the IVC. Typically after exiting the renal hilum, the left renal vein receives a lumbar vein posteriorly, the left gonadal vein inferiorly, and the adrenal vein superiorly. Next, the left renal vein crosses anterior to the aorta and under the caudal edge of the superior mesenteric artery before draining into the IVC. Rarely the left renal vein crosses the aorta to the IVC in a retroaortic or circumaortic path.

Proceeding cranially, the posterior aspect of the IVC receives the right adrenal vein. This short vein is located posteriorly on the IVC, making it challenging to expose during right adrenal or renal surgery. As noted already, the left adrenal vein drains into the left renal vein as opposed to the IVC. The inferior phrenic vein on the right side enters along the posterior or posterior lateral aspect of the IVC, with the left inferior phrenic vein typically entering the left renal vein. The final tributaries to the IVC before it leaves the retroperitoneum are the short hepatic veins draining the liver. Inferiorly these veins are small, but superiorly three large hepatic trunks are encountered.

Lymphatics

Lymphatic drainage of the lower extremities, external genitalia, testes, kidneys, and intestines is located in the retroperitoneum ( Fig. 1-13 ). Knowledge of these lymphatic channels is useful not only for urologic oncology (e.g., testis cancer) but also for prevention of complications such as lymphocele. Drainage of the lower extremities, perineum, and external genitalia progresses through the retroperitoneum via common iliac lymph vessels and then forms ascending vertical lumbar lymphatic chains. There is flow not only cranially but also laterally, predominantly from the right to the left. Gastrointestinal lymphatic drainage also follows the vascular supply, with the majority of the lymphatics paralleling the inferior mesenteric, superior mesenteric, and celiac arteries. Eventually these lymphatics join posterior to the aorta at the level of the first or second lumbar vertebrae to form the thoracic duct. This coalescence is classically marked by a local dilation called the cisterna chyli, which tends to lie within the thorax just to the right of the aorta in a retrocrural position.

Figure 1-13 Retroperitoneal lymphatics. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 335.)

For the urologist, the lumbar lymphatics are important as the primary lymphatic drainage from two urologic organs: the kidneys and testes. Given the kidney's retroperitoneal location, the lumbar path of its lymphatic drainage is not surprising and is discussed in more depth later in this chapter. Embryologically, the testes develop within the retroperitoneum and maintain both blood flow (testicular arteries) and lymphatic drainage through this area even after they descend into the scrotum. To better describe the lymphatic drainage within the retroperitoneum a practical system has been developed. This system defines three major nodal areas: right paracaval, interaortal caval, and left para-aortic. The right paracaval nodal region extends from the midline of the IVC to the right ureter. The interaortal caval region extends from the midline of the IVC to the midline of the aorta, and the left para-aortic region extends from the midline of the aorta to the left ureter.

Study of lymphatic metastases from testicular tumors have shown that testicular lymphatic drainage is consistent and follows the general scheme of vertical drainage with lateral flow from right to left. Lymphatic metastases from the right testis drain primarily into the interaortal caval nodes with significant drainage to the right paracaval nodes. In addition there is a small amount of drainage to the left para-aortic nodes. On the other hand, the left testis drains primarily to the left para-aortic nodes with significant drainage to the interaortal caval nodes. There is essentially no drainage to the right paracaval nodes from left-sided tumors.

Nervous System Structures

The nervous structures within the retroperitoneum are part of the peripheral nervous system and can be divided into two categories: autonomic and somatic nerves. The autonomic nerves provide afferent and efferent innervation to organs, blood vessels, glands, and smooth muscles. They are further characterized by the presence of peripheral synapses. Thus there are least two peripheral nerves between the central nervous system and the viscera. The somatic nerves supply afferent and efferent innervation to the skin, skeletal muscles, and joints. Although these two nerve types leave the spinal column within shared spinal nerves, their course and functions quickly diverge.

Autonomic System

The autonomic system is further divided into sympathetic and parasympathetic fibers. The origin of these two nerve types is quite different, with the sympathetic preganglionic fibers originating from the thoracic and lumbar portions of the spinal column and the parasympathetic preganglionic fibers beginning in the cranial and sacral spinal column segments. Preganglionic sympathetic fibers enter the retroperitoneum through both the paired sympathetic chains and input from the lumbar spinal nerves ( Fig. 1-14 ). The lumbar portion of this sympathetic chain then sends preganglionic fibers to autonomic plexuses associated with the major branches of the abdominal aorta. Within these aortic plexuses the preganglionic fibers synapse and postganglionic fibers are then distributed to the various abdominal viscera and organs. Parasympathetic input from the vagus nerve also supplies these ganglia.

Figure 1-14 Sympathetic chain and splanchnic nerves. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 309.)

In more detail, the thoracic and lumbar portions of the sympathetic chain originate from preganglionic sympathetic fibers arising from the first thoracic through the third lumbar spinal nerves (see Fig. 1-14 ). This chain then courses vertically along the anterolateral aspect of the spine just medial to the psoas muscle. Within the retroperitoneum lumbar arteries and veins are closely associated with the lumbar sympathetic chain, in some instances even splitting the fibers as they cross the chain perpendicularly. From this sympathetic chain preganglionic fibers follow one of three courses. First, preganglionic fibers are sent to the various autonomic plexuses (splanchnic nerves). Once in the plexus, the preganglionic fibers synapse within a ganglion to postganglionic fibers, which in turn proceed to the abdominal viscera. Second, preganglionic fibers can synapse within the sympathetic chain ganglia and send postganglionic fibers to the body wall and lower extremities. Finally, preganglionic sympathetic fibers can proceed directly to the adrenal gland without synapsing. Within the adrenal medulla, these preganglionic fibers control release of catecholamines.

The major autonomic nerve plexuses are associated with the primary branches of the aorta. These plexuses include the celiac, superior hypogastric, and inferior hypogastric plexuses ( Fig. 1-15 ). These plexuses receive sympathetic input from the sympathetic chains via the greater, lesser, and least thoracic splanchnic nerves originating from the 5th through 12th thoracic spinal nerves. They also receive input from the lumbar portion of the sympathetic chain via the lumbar splanchnic nerves as well as parasympathetic input via the vagus nerve.

Figure 1-15 Autonomic plexuses associated with branches of the aorta. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 337.)

The largest is the celiac plexus and is located to either side of the celiac arterial trunk as a paired structure. It is through this plexus that much or all of the autonomic input to the kidney, adrenal, renal pelvis, and ureter passes. In addition, some of the sympathetic innervation to the testes passes through this ganglion before continuing in parallel with the testicular artery to the testis. A separate aorticorenal ganglion usually exists as an inferior extension of the celiac ganglion, forming part of the renal autonomic plexus. The latter plexus surrounds the renal artery and its branches and is contiguous with the celiac plexus. At the lower extent of the abdominal aorta, much of the autonomic input to the pelvic urinary organs and genital tract travels through the superior hypogastric plexus. This plexus lies on the aorta anterior to its bifurcation and extends inferiorly on the anterior surface of the fifth lumbar vertebra. This plexus is contiguous bilaterally with inferior hypogastric plexuses, which extend into the pelvis. Disruption of the sympathetic nerve fibers that travel through these plexuses during retroperitoneal dissection can cause loss of seminal vesicle emission and/or failure of bladder neck closure, resulting in retrograde ejaculation.

Somatic

The somatic sensory and motor innervation to the abdomen and lower extremities arises in the retroperitoneum and is called the lumbosacral plexus. The lumbosacral plexus is formed from branches of all lumbar and sacral spinal nerves, with some contribution from the 12th thoracic spinal nerve as well ( Fig. 1-16 ). Superiorly, nerves of this plexus form within the body of the psoas muscle and pierce this muscle, with more inferior branches passing medial to the psoas as the pelvis is entered ( Fig. 1-17 ). The origins and functions of these lumbosacral somatic nerves are summarized in Table 1-3 .

Figure 1-16 Diagrammatic representation of the lumbosacral nervous plexus.

Figure 1-17 Lumbar plexus in the posterior abdominal region. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 341.)

Table 1-3 -- Branches of the Lumbosacral Plexus

Branch	Origin	Spinal Segments	Function: Motor	Function: Sensory
Iliohypogastric	Anterior ramus L1	L1	Internal oblique and transversus abdominis	Posterolateral gluteal skin and skin in pubic region
Ilioinguinal	Anterior ramus L1	L1	Internal oblique and transversus abdominis	Skin in the upper medial thigh, and either the skin over the root of the penis and anterior scrotum or the mons pubis and labium majus
Genitofemoral	Anterior rami L1 and L2	L1, L2	Genital branch—male cremasteric muscle	Genital branch—skin of anterior scrotum or skin of mons pubis and labium majus; femoral branch—skin of upper anterior thigh
Lateral cutaneous nerve of thigh	Anterior rami L2 and L3	L2, L3		Skin on anterior and lateral thigh to the knee
Obturator	Anterior rami L2 to L4	L2 to L4	Obturator externus, pectineus, and muscles in medial compartment of thigh	Skin on medial aspect of the thigh
Femoral	Anterior rami L2 to L4	L2 to L4	Iliacus, pectineus, and muscles in anterior compartment of thigh	Skin on anterior thigh and medial surface of leg

From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 340.

The subcostal nerve is the anterior extension of the 12th thoracic nerve and extends laterally beneath the 12th rib. As one proceeds inferiorly, the iliohypogastric nerve and the ilioinguinal nerve originate together as an extension from the first lumbar spinal nerve. These three nerves cross the anterior or inner surface of the quadratus lumborum muscle before piercing the transversus abdominis muscle and continuing their course between this and the internal oblique muscle. Together they provide multiple motor branches to the muscles of the abdominal wall as well as sensory innervation to the skin of the lower abdomen and genitalia. The lateral femoral cutaneous nerve and the genitofemoral nerve arise from the first through third lumbar nerves and are primarily sensory nerves to the skin of the upper thigh and genitalia; however, the genital branch of the genitofemoral nerve also supplies the cremaster and dartos muscles in the scrotum. The genitofemoral nerve lies directly atop and parallels the psoas muscle throughout most of its retroperitoneal course and is easily identified in this position.

The femoral nerve is a larger structure arising from the second through fourth lumbar spinal nerves and is largely hidden by the body of the psoas muscle before exiting the abdomen just lateral to the femoral artery. This important nervous structure supplies the psoas and iliacus muscles as well as the large muscle groups of the anterior thigh. It also provides sensory innervation of the anteromedial portions of the lower extremity. Intraoperatively, it may be compressed by retractor blades placed inferolaterally against the inguinal ligament in lower abdominal incisions, producing a significant motor palsy that prevents active extension of the knee.

The final lumbosacral plexus nerves include the obturator and sciatic nerves. The obturator nerve, an important pelvic landmark, arises behind the psoas muscle in the retroperitoneum from the third and fourth lumbar spinal nerves. It then courses inferiorly, where its major function is to supply the adductor muscles of the thigh. The sciatic nerve receives input from the fourth lumbar through third sacral spinal nerves, taking final form in the deep posterior pelvis as the body's single largest nerve, supplying the bulk of both sensory and motor innervation to the lower extremity.

Duodenum, Pancreas, Colon ( Fig. 1-18 )

The duodenum is divided into four anatomic components. The first (ascending) portion is short (5 cm) and intimately related to the gallbladder. The second (descending portion) is of most importance to the urologist because it lies immediately anterior to the right renal hilum and pelvis. This portion of the duodenum is frequently mobilized (referred to as a Kocher maneuver) to expose the right kidney, right renal pelvis, and additional upper abdominal structures. The second portion of the duodenum also receives the common bile duct and surrounds the head of the pancreas. The third (horizontal) and fourth (ascending) portions of the duodenum cross from right to left over the IVC and aorta before transitioning into the jejunum.

Figure 1-18 Colon, duodenum, and pancreas within the retroperitoneum. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 274.)

As noted earlier, the head of the pancreas is on the medial border of the descending duodenum. The body and tail of the pancreas continue across the IVC and aorta to the left side of the abdomen where the pancreas is closely related to the left adrenal gland and the upper pole of the left kidney. The splenic artery and vein travel laterally along the posterior aspect of the pancreas, with the artery just superior to the vein. In this position these vascular structures are also closely related to the upper pole of the left kidney.

The final retroperitoneal gastrointestinal structure is the colon, with the ascending and descending portions being retroperitoneal. Both the ascending colon at the hepatic flexure and descending colon at the splenic flexure overlie the ipsalateral kidney. In addition, the hepatocolic ligament and splenocolic ligament tether the liver and spleen to the respective portions of the colon. Given the close anatomic relationship to the kidneys, mobilization of the colon and its mesentery is important for transperitoneal exposure of the kidneys and ureters.