Perirenale

Perirenale, or perirenal, refers to the anatomical region surrounding the kidney within the retroperitoneum. This space is bounded by the renal fascia, also known as Gerota's fascia, which encloses the kidney and adrenal gland together with their perirenal fat, forming the perirenal space. The space extends from the superior region near the diaphragmatic crura to the lower abdomen near the iliac crest, and lies between the anterior and posterior layers of the renal fascia, which fuse laterally to create a continuous enclosure.

Contents and boundaries are defined by the surrounding fascia. The perirenal space contains the kidney with its fibrous capsule, the adrenal gland, the proximal portion of the ureter, perirenal fat, portions of the renal vessels and lymphatics, and the sympathetic nerve plexus. Medially the space interfaces with other retroperitoneal compartments and is bordered anteriorly by the posterior surface of the peritoneum and posteriorly by the posterior layer of the renal fascia; laterally, it blends with surrounding fascia and fat.

Clinical relevance arises from the space’s role as a potential site for pathology. Perirenal involvement can occur with infections such as perirenal abscess, traumatic or iatrogenic hemorrhage leading to a perirenal hematoma, or urine leakage forming a urinoma when the collecting system is disrupted. Inflammation or infection can cause fat stranding or fluid collections visible on imaging, and the fascial boundaries influence the spread of disease within the retroperitoneum.

Imaging typically shows the perirenal fat as a distinct radiodensity around the kidney on CT, with any abnormal fluid, air, or enhancement indicating pathology. Ultrasound can detect fluid collections and assess surrounding structures; CT or MRI provides detailed delineation of fascial planes and extent of disease. See also: retroperitoneum, renal fascia, Gerota's fascia.