Renal sinus lipomatosis is the accumulation of excessive nontumorous fatty tissue within the renal sinus. In the normal young adult, a thin layer of loose fatty tissue envelops the pelvocalyceal and vascular structures which traverse the sinus. In the course of normal aging this layer undergoes a slight, gradual increase. Under extraordinary conditions the amount of fat in the renal sinus is so excessive that pelvocalyceal deformity results. The most obvious of these conditions is massive obesity. Proliferation of fat also occurs when there is loss of renal parenchyma as the result of infection, infarction, or arteriosclerotic ischemia. In a small number of cases lipomatosis occurs without evident cause. This entity has been referred to as fibrolipomatosis (11, 14), fatty replacement (3–6, 8, 10, 16, 18, 19, 23), fatty transformation (17), lipomatous paranephritis, and lipoma diffusum renis (8). Since neither replacement phenomena nor fibrosis are invariably present, we prefer the general term renal sinus lipomatosis as one which encompasses all variants of the process. Renal sinus lipomatosis should not be confused with lipomas (15) or hamartolipomas (9) which are true tumors arising from embryonic rests within the renal substance. There should be no confusion between lipomatosis and either fatty degeneration of the kidney or lipoid nephrosis, both of which are characterized by intracellular lipid deposition. Anatomy The renal sinus (Fig. 1) is a shallow depression on the medial aspect of the kidney through which pass the infundibula, part or all of the renal pelvis, and the renal arteries, veins, lymphatics, and nerves. The sinus is lined by an invagination of the renal capsule, which is perforated by the calyces and vessels as they enter the renal substance. These perforations are tightly sealed so that there is no communication between the sinus and the parenchyma. The fatty tissue within the renal sinus is continuous with the perirenal fat through crevices between the hilar structures (Fig. 2) (7, 12, 13). Nephrotomographic Technic The technic of nephrotomography proposed by Evans and his associates (1, 3) is simple and safe and provides a favorable radiographic setting for the diagnosis of lipomatosis. A large volume of concentrated opaque material is injected via an antecubital vein. Either a single exposure or a series of rapid sequence exposures are made over the lumbar region, commencing with the predetermined circulation time. These films show the contrast agent in the renal vessels. Immediately thereafter, the large bolus of opaque material induces a marked nephrogram which lasts several minutes. Tomograms are made in the anteroposterior and posterior oblique projections during this nephrogram phase. The nephrotomographic phase thus obtained is of great value in the diagnosis of lipomatosis. The lucent, avascular fat is boldly contrasted against the brightly opacified renal parenchyma.
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Faegenburg et al. (1964) studied this question.