It is of paramount importance that the Urologic surgeon possess a comprehensive anatomic understanding of the retroperitoneal compartment given that in this space, and the contiguous extravesical domain below the peritoneal reflection, reside all the major urologic organs. Moreover, traversing the retroperitoneum are the body’s primary blood vessels—the aorta and inferior vena cava (IVC)—from which emerge the vascular supply to the urologic organs. As control of arterial and venous structures is often a critical component to surgery, particularly when performed for an oncologic indication, familiarity with both the conventional and variant anatomic course of these vessels as they approach their target organ is essential. Within the retroperitoneal space is also a rich lymphatic network intimately associated with the aorta and IVC. Secondary infiltration of these lymphatics by kidney, upper tract urothelial, and primary testicular germ cell tumors may necessitate surgical resection of the peri-caval and peri-aortic lymph nodes, emphasizing the importance of understanding principles by which the retroperitoneal compartment is accessed.
Herein, we review the structural organization of the retroperitoneal space, highlighting how the anatomy of this compartment is maneuvered during major urologic procedures, performed via either an open or laparoscopic approach.
The retroperitoneum is bounded anteriorly by the parietal peritoneal layer and posterolaterally by the transversalis fascia. The compartment itself rests upon the belly of the psoas and paraspinal (specifically the quadratus lumborum) muscles, over which lies the lumbodorsal fascia—a connective tissue layer that is itself continuous more laterally with the transversalis fascia (Fig. 1.1).
The retroperitoneum can be divided further into four compartments, which from a surgeon’s perspective aids in the understanding of access to the urologic organs and major blood vessels situated within this space. These compartments include the Perirenal Space, the Anterior Pararenal Space, the Posterior Pararenal Space, and the Central Vascular Compartment (Figs. 1.2a, b).
The perirenal space contains within it the adrenal gland, kidney, and ureter—organs that are all supported by a body of perinephric fat. The volume of fat within this compartment varies widely and is based partly on age, gender, and body mass (Fig. 1.3). The perirenal space is delineated anteriorly by Gerota’s fascia (anterior perirenal fascia) and posteriorly by Zuckerkandl’s fascia (posterior perirenal fascia), which fuse laterally to essentially envelop these organs and overlying fat layer (Fig. 1.2c). The point of fusion along the lateral contour of the kidney is of clinical relevance as it offers a nice cleavage plane through the perinephric fat by which the capsular kidney surface can be accessed, as is necessary during partial nephrectomy.
The posterior perirenal fascia is in fact comprised of two layers, the deep and superficial lamina, which explains its prominence on cross-sectional imaging. Whereas the deep layer is continuous with the anterior renal fascia, the superficial layer of the perirenal fascia deviates anteriorly off the lateral contour of the perirenal space, and is referred to here as the lateral conal fascia. The lateral conal fascia runs along the lateral edge of the anterior pararenal space as it fuses here with the parietal peritoneum (Fig. 1.2c).
The perirenal space is shaped as an inverted pyramid, with the diaphragm serving as the base of this space and the apex of the space directed towards the pelvis. Although the superior border of the perirenal space is solely the diaphragm on the left (Fig. 1.4), the superior border of the perirenal compartment on the right is formed anteriorly by the bare segment of the liver, which is devoid of a peritoneal lining, and posteriorly by the diaphragm (Fig. 1.5). The perirenal space rests on top of the psoas and quadratus lumborum muscles; this interface is formed by close apposition of the Zuckerkandl fascia with the psoas fascia and thoracodorsal fascia, which overlie the psoas and quadratus lumborum muscles, respectively (Figs. 1.2c and 1.6).
Piercing the perirenal fascia medially are renal hilar vessels, which are derived from the great vessels situated within the central vascular compartment (Fig. 1.7). Although the right and left perirenal spaces are separated by this central vascular compartment, cross-talk is thought to exist between them, particularly given the anatomic configuration of Gerota’s fascia whereby it crosses the midline to drape over the great vessels at the level of the L3 to L5 vertebrae to fuse with the Gerota’s fascia of the contralateral side (Fig. 1.2c). Indeed, it is proposed that trabeculae within the anterior perirenal fascia connective tissue crossing the midline forms the Kneeland channels, allowing for communication between both perirenal spaces .
The ureter is the most posterior structure within the renal hilum, resting behind the renal vessels. It descends within the perirenal space on the anterior surface of the psoas muscle and associated fascia (Fig. 1.8). It courses lateral to the gonadal vein—an important anatomic consideration during urologic procedures in the retroperitoneum. When performing laparoscopic nephrectomy or nephroureterectomy, the gonadal vein should be kept medial (particularly for right-sided procedures) and the ureter displaced anterolateral off the psoas muscle to facilitate dissection towards to renal hilum; this maneuver helps separate the perirenal space (via Zuckerkandl’s fascia) off the psoas muscle and is critical in preventing violation of the perirenal fat (Fig. 1.8). Similarly, during retroperitoneal lymph node dissection, the ureter is identified and swept laterally and the gonadal vein kept medially so as to create a space between the perirenal space and central vascular compartment (Fig. 1.9) as well as facilitate ligation of the gonadal vein.
The ureter in its descent will subsequently course medially and travel underneath the gonadal vein and artery—an anatomic relationship that is often referred to by the aphorism “water under the bridge.” It will eventually cross over the common iliac artery just proximal to its bifurcation and dive medially to enter the bladder under the shade of the superior vesical artery.
Anterior Pararenal Space
The anterior pararenal spaceis situated directly in front of the perirenal spaces laterally and the central vascular compartment medially. It is bounded anteriorly by the parietal peritoneum and posteriorly by the Toldt’s fascia, which directly overlies and is opposed to the anterior leaf of the perirenal fascia (Gerota’s fascia) (Fig. 1.2e). The anterior pararenal space contains the ascending colon, its mesocolon, and the duodenum on the right and the descending colon along with its mesocolon on the left. The pancreas also resides here with the head oriented towards the right, the tail towards the left, and the pancreatic body in the midline anterior to the central vascular compartment.
Transperitoneal access to the kidney and ureter (perirenal space) as well as the major vessels (central vascular compartment) requires sufficient reflection of structures not only within the peritoneal cavity (intraperitoneal location), but also within the anterior pararenal space. In this regard, it is helpful to understand the relationship of the anterior pararenal space to the intraperitoneal contents.
As aforementioned, the anterior pararenal space is limited anteriorly by the posterior wall of the peritoneal cavity, which is formed by a sheet of mesothelial tissue referred to as the parietal peritoneum (Figs. 1.2 and 1.10) . The perpendicular projection of this mesothelial layer into the peritoneal space is referred to as the visceral peritoneum as it lines the mesentery of the small intestine, which is in an intraperitoneal location. At the level of this small bowel peritoneal reflection, the small bowel mesentery has a broad base that obliquely runs from the duodeno-jejunal flexure (left upper quadrant) towards the cecum (right lower quadrant), essentially mounting the small bowel to the posterior abdominal wall via its mesentery (Fig. 1.10). Invested within the thin fibroadipose layer of the small bowel mesentery are blood vessels derived from the superior mesenteric artery and vein accompanied by lymphatics. In fact, although the small bowel mesentery is attached to the posterior abdominal wall by a broad base, the root of this mesentery is situated primarily around the takeoff of the superior mesenteric artery such that if the small bowel mesentery were detached from its broad-based attachment, it would remain suspended by the SMA, which would essentially serve as a point of pivot (Fig. 1.10).