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Anterior pararenal space

Dr Jeremy Jones et al.

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

Medially, the space is in continuity with the opposite side. There is a paucity of fat within the compartment and therefore, is it difficult to identiy 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.

Fluid extends throughout the space until it reaches its boundaries:

medially : there is continuity with the other side 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 oesophagus 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 vas deferens and even into the femoral sheath

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