Mass effect in the renal sinus: an anatomic classification

Before the advent of modern imaging techniques, pathologic processes in the renal sinus were diagnostic enigmas. Many of the conditions create nonspecific deformities of the contrast-filled collecting system. In the past, the discovery of these abnormalities often led to unnecessary exploration. Modern imaging techniques usually allow a specific diagnosis to be made, but because a number of the pathologic conditions affecting the renal sinus have similar appearances on a single type of imaging study, complete delineation may require correlation of a number of diagnostic techniques. An understanding of the normal sinus anatomy allows classification of pathologic processes that occur in this region and ensures an orderly imaging investigation. The anatomic classification is based on the structure from which the mass arises. The source of the mass may be any structure within the renal sinus (intrinsic), the enveloping renal parenchymal (adjacent), or a source outside the kidney itself with subsequent sinus involvement (extrinsic). This classification will be used to review a number of pathologic processes that occur in the renal sinus and pertinent imaging features.