Caudally, fusion of the anterior and posterior layers is incomplete, which allows perinephric fluid to seep into the iliac fossa of the greater pelvis. Likewise, air injected into the presacral space is known to reach the perinephric space through this same opening; this technique was formerly used to visualize the kidneys in a procedure known as retroperitoneal pneumography.

External to the renal fascia lies the retroperitoneal paranephric fat (pararenal fat body), a continuation of the extraperitoneal fat. The perinephric and paranephric fat are both traversed by variably developed strands of collagenous connective tissue that extend from the renal fascia, which may cause them to appear multilaminate in sectional studies.