The anterior pararenal space is the portion of the retroperitoneum that lies between the posterior surface of the parietal peritoneum and the anterior reflection of the perirenal fascia.

Gross anatomy

It contains the duodenum (D2 and D4), pancreas and retroperitoneal segments of the ascending and descending colon. It also contains the roots of the small bowel mesentery and transverse mesocolon.

Boundaries

medially: there is continuity with the contralateral anterior pararenal space although in most cases, fluid will lateralize to the side of pathology
laterally: the compartment is limited as the lateroconal fascia and parietal peritoneum merge
superiorly: fluid may extend to the dome of the diaphragm immediately posterior to the esophagus and phrenicoesophageal ligament
inferiorly: fluid may extend to the iliac fossa, from there into the pelvis and potentially to the rectus sheath, around the round ligament or ductus deferens and even into the femoral sheath

Radiographic features

There is a paucity of fat within the compartment and therefore, it is difficult to identify on CT or MRI in patients with no additional pathology.

When fluid collects within the anterior pararenal space it becomes easier to identify on CT or MRI. Additionally, because the perirenal fascia is bilaminated, fluid in the compartment can dissect between the anterior and posterior fascia and sit behind the kidney.

Additionally, fluid can dissect along ligaments and mesenteries to lie in the subperitoneal space, e.g. gastrosplenic ligament, transverse mesocolon and greater omentum.