Introduction to the Retroperitoneum

Relevant Anatomy and Embryology

The parietal peritoneum separates the peritoneal cavity from the retroperitoneum. The retroperitoneum contains all the abdominal contents located between the parietal peritoneum and the transversalis fascia. It is divided into 3 compartments by 2 well-defined fascial planes: The renal and lateroconal fasciae.

The perirenal space contains the kidney, adrenal, proximal ureter, and abundant fat, and it is enclosed by the renal fascia, which is also referred to as Gerota fascia. The perirenal spaces can communicate across the abdominal midline as shown through in vivo and cadaveric injection studies.

The anterior pararenal space contains the pancreas, duodenum, colon (ascending and descending), and a variable amount of fat.

The posterior pararenal space contains fat but no organs; it is contiguous with the properitoneal fat along the flanks.

The anterior renal fascia separates the perirenal space from the anterior pararenal space, and the posterior renal fascia separates the perirenal space from the posterior pararenal space.

The lateroconal fascia separates the anterior from the posterior pararenal space and marks the lateral extent of the anterior pararenal space.

The renal fascia joins and closes the perirenal space resembling an inverted cone with its tip in the iliac fossa. Caudal to the perirenal space, in the pelvis, the anterior and posterior pararenal spaces merge to form a single infrarenal retroperitoneal space, which communicates directly with the pelvic prevesical space (of Retzius). Due to an opening in the cone of the renal fascia caudally, the perirenal space communicates with the infrarenal retroperitoneal space. Thus, all 3 retroperitoneal compartments communicate with each other within the lower abdomen and pelvis. All of the pelvic retroperitoneal compartments, such as the perivesical and perirectal spaces, communicate with each other, which is evident and clinically relevant in cases of pelvic hemorrhage or tumor as well as with extraperitoneal rupture of the urinary bladder.

The renal and lateroconal fascia are laminated planes, which can split to form potential spaces as pathways of spread for rapidly expanding fluid collections or inflammatory processes, such as hemorrhage or acute pancreatitis. Splitting of the anterior renal fascia creates a "retromesenteric plane" that communicates across the midline; splitting of the posterior renal fascia creates a "retrorenal plane," which also communicates across the midline and anteriorly. Knowing this principle is crucial to understanding how diseases originating in the anterior pararenal space, such as acute pancreatitis, can extend posterior to the back of the kidney or how fluid collections within the posterior pararenal space or retrorenal plane can extend around the lateral or even anterior abdominal wall.