Bridging septa of the perinephric space: anatomic, pathologic, and diagnostic considerations

The perinephric space is not a simple fat-filled chamber through which fluid may be distributed unhindered. It is divided into multiple compartments by fibrous lamellae, the bridging septa. Some of these structures arise from the renal capsule and extend to the perinephric fascia; others are attached only to the renal capsule and are arranged more or less parallel to the renal surface. Still others connect the anterior to the posterior leaves of the perinephric fascia. The resulting compartments exert an important influence on pathologic processes, resulting, for example, in limitation of the spread of pus and tamponade of bleeding points. The configuration of many perinephric collections can only be understood by knowledge of the existence and arrangement of these lamellae. The current criteria for differentiation of subcapsular from perinephric hematomas are shown to be in error, and a new sign for such differentiation is described. There are also implications regarding therapeutic drainage of perinephric abscesses, particularly by the percutaneous route. A new classification of the perinephric fascia is proposed.