Alteration of perirenal fat secondary to diffuse retroperitoneal infiltration

Inflammatory effusions and diffuse neoplasia in the fatty retroperitoneal space, which can alter the perirenal fat, can be recognized radiographically because of density differences. The opacity of fluid and tumor accentuates the remaining fat which conforms to the renal contour. This perirenal fatty border appears as a lucent strip when the perirenal fat is not violated and as abnormal perirenal streakiness when the perirenal fat is infiltrated by fluid or tumor. Six cases are described.