Anatomy of adipose compartments and fascial structures in the posterolateral region of the kidney with special focus on the thin adipose compartment

Objectives To anatomically and histologically define adipose and fascial structures posterior and lateral to the kidney and propose a compartment-based anatomical model aligned with intraoperative observations. Methods Seven cadavers were used for macroscopic and histological analyses. In the macroscopic analysis, the spatial relationships between the perirenal fat, pararenal fat, posterior renal fascia, and extraperitoneal fascia were examined. Histological observations focused on the distribution and continuity of adipose compartments and the organization of the surrounding dense fibrous connective tissues. Results Macroscopically, the extraperitoneal fascia covered the anteromedial pararenal fat and extended posteriorly to the kidney. Upon incision, a small amount of adipose tissue was observed directly beneath it. Removing this thin adipose layer exposes the peritoneum and posterior renal fascia, with a clear demarcation between them. Histological analysis confirmed that the posterior renal and extraperitoneal fascia were distinct, with dense connective tissue structures enclosing a separate, thin adipose compartment. This compartment extended anteriorly between the perirenal fat and peritoneum, and laterally between the peritoneum and extraperitoneal fascia. These extensions converge near the peritoneal reflection in the lateral renal region, forming the characteristic triradiate configuration of the adipose tissue. Conclusions Our findings challenge the classical notion that the renal fascia is a single continuous layer supporting a compartment-centered anatomical model. The posterior and lateral regions of the kidney contain a distinct third adipose compartment bordered by the posterior renal and extraperitoneal fasciae. This model offers improved anatomical clarity and may aid understanding during laparoscopic, retroperitoneoscopic, and robot-assisted surgeries.