1. Gross and Laparoscopic Anatomy of the Upper Tract and Retroperitoneum

Paras H. Shah¹ and Bradley C. Leibovich¹

(1)

Division of Urology, Albany Medical Center, Albany, NY, USA

Paras H. Shah

Email: Shah.Paras@mayo.edu

Bradley C. Leibovich (Corresponding author)

Email: Leibovich.Bradley@mayo.edu

Keywords

Retroperitoneum anatomyRetroperitoneal surgeryLaparoscopyNephrectomyRetroperitoneal lymph node dissectionPerirenal spaceAnterior pararenal spaceCentral vascular compartmentGerota’s fascia

Introduction

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.

Anatomy

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).

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Retroperitoneum vs. peritoneal cavity: the boundaries of the retroperitoneal space, which is highlighted in yellow, are formed by the parietal peritoneum (red) and the transversalis fascia (green). The retroperitoneal compartment is continuous anteriorly with the pre-peritoneal space (dense yellow shade). Within the retroperitoneum are bilateral Kidneys (K), the 2nd and transverse segments of the Duodenum (D), Ascending Colon at the level of the hepatic flexure (AC), Descending Colon below the splenic flexure (DC), Aorta (A) and Inferior Vena Cava (*IVC*). Additionally, the Liver (L), Gallbladder (GB), Transverse Colon (TC) and Jejunal loops of small intestine are appreciated within the intraperitoneal space

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).

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Cross-sectional image of CT abdomen. (a) Cross-section image of CT abdomen. (b) Divisions of the Retroperitoneum: The peritoneal cavity is lined by a layer of mesothelial tissue referred to as the parietal peritoneum (yellow). The retroperitoneum can be subdivided into four compartments: the perirenal space (blue/green), the central vascular compartment (red), the anterior pararenal space (yellow/orange lines), and the posterior pararenal space (purple). (c) Perirenal Space: The Kidneys (K) are situated within the perirenal space, which is bordered by the Gerota’s fascia anteriorly (green) and the Zuckerkandl’s fascia posteriorly (blue). Additionally, the Gerota’s fascia crosses over the midline (dashed green) as it drapes over the central vascular compartment to connect to the contralateral perirenal space; within this are the Kneeland’s channels, which may allow for communication between the spaces. The Zuckerkandl’s fascia continues anteriorly (blue) off the lateral contour of the kidney, forming the lateral border of the anterior pararenal space and connecting to the parietal peritoneum. The perirenal space rests on top of the psoas (P) and Quadratus Lumborum (QL) muscles. (d) Central Vascular Compartment: The Aorta (A) and Inferior Vena Cava (*IVC*) are located within the central vascular compartment, outlined in red and shaded in purple. Peri-aortic and peri-caval lymph nodes are within the surrounding fibroadipose tissue. The Gerota’s fascia can be seen crossing the midline and draping over the central vascular compartment (dashed green lines). (e) Anterior Pararenal Space: Seen here within the Anterior Pararenal Space, which is outlined in yellow anteriorly and orange posteriorly, is the Ascending Colon (AC), the Duodenum (D), and the Descending Colon (DC). The anterior connective tissue border of this space is formed anteriorly by the parietal peritoneum (yellow), which serves as the posterior abdominal wall of the peritoneal compartment, and posteriorly by the Toldt’s fascia (orange). (f) Posterior Pararenal Space: This compartment, outlined in purple, contains only adipose tissue

Perirenal Space

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.

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Perinephric fat. (a) Intraoperative view of the Kidney with the surrounding Perinephric fat removed off its capsular surface. (b) A large volume of perinephric fat, as delineated by yellow arrows, is appreciated around both kidneys. The anterior and posterior perirenal fascia are delineated in green and blue, respectively. (c) Minimal perinephric fat volume, as delineated by yellow arrows, is appreciated around both kidneys. The anterior and posterior perirenal fascia are delineated in green and blue, respectively

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).

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Left perirenal space. (a) The superior border of the left perirenal space is the diaphragm (red). The anterior and posterior perirenal fascia are delineated in green and blue, respectively. (b) Medial reflection of the left mesocolon permits access to the left perirenal space. (**c, d**) Division of the splenorenal ligament permits medial reflection of the spleen (intraperitoneal location) off the superior aspect of the left perirenal space. DC descending colon, K kidney, S spleen

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Right perirenal space. (a) The superior border of the right perirenal space is formed by both the bare segment of liver (anteriorly; yellow) and the diaphragm (posteriorly; red). The anterior and posterior perirenal fascia are delineated in green and blue, respectively. (b) Intraoperative view of the intraperitoneal portion of liver. (c) The bare segment of the liver, serving as the superior border of the right perirenal space, can be visualized upon accessing the upper region of the right perirenal space. Of note, the adrenal gland and surrounding perirenal fat have been removed. K Kidney, L liver

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The posterior perirenal fascia of the right (a) and left (b) perirenal spaces is lifted anteriorly off the Psoas muscle/fascia

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 [1].

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Renal hilum. (a) The major renal vessels (RA and RV) pierce the perirenal fascia medially, exiting the central vascular compartment (encircled in red) to enter the hilum of the perirenal space (green and blue). The RA is generally situated posterior to the RV, with the right RA assuming a retrocaval location. (b, c) The renal vessels can be visualized within the hilum of the right (b) and left (c) kidney. A aorta, *IVC* inferior vena cava, RA renal artery, RV renal vein

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.

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The ureter is situated within the posterior-medial aspect of the perirenal compartment. As the perirenal compartment is lifted anteriorly off the psoas muscle, the ureter can be seen on the posterior-medial aspect of the plane that is created. RV renal vein

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Separation of the perirenal space and the central vascular compartment is facilitated by identification and lateralization of the ureter so as to separate it off from the lateral border of the IVC on the right (a) and the from the lateral border of the Aorta on the left (b). White vessel loops are used to isolate postganglionic sympathetic fibers. *CIA* common iliac artery, *IVC* inferior vena cava, RV renal 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 space is 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) [2]. 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).