Anatomy of the retroperitoneum: observations of the distribution of pathologic fluid collections.

Purpose: To correlate anatomic dissections with clinical observations regarding anatomic distribution of retroperitoneal fluid, and to document the existence of planes that lie between classically described retroperitoneal spaces.

Materials And Methods: Latex was injected in varying amounts into the pancreatic tail in three fresh cadavers to simulate peripancreatic fluid collections. Spiral computed tomography (CT) was performed of the abdomen and pelvis after each latex injection. Two cadavers were subsequently frozen and sectioned in axial planes; limited dissections were performed on these specimens. One was embalmed and underwent extensive anatomic dissection. Five embalmed, unprepared cadavers were also dissected to confirm observations made in the three prepared cadavers.

Results: Latex injected into the tail of the pancreas entered a retromesenteric plane that was posterior to the anterior pararenal space and anterior to the anterior renal fascia. The plane continued superiorly, extending to the diaphragm near the esophageal hiatus; inferiorly, extending to the pelvis along the anterolateral surface of the psoas muscle; and laterally, posterior to the descending colon and its mesentery. The plane also communicated with a retrorenal plane lying between the posterior renal fascia and the posterior pararenal space.

Conclusion: Embryologic development of the dorsal mesenteries suggests the existence of retromesenteric planes, and clinical observations further support their existence. These findings may explain the observed distribution of retroperitoneal fluid collections from diaphragm to pelvis.