Renal papillary necrosis: review and comparison of findings at multi-detector row CT and intravenous urography.

Renal papillary necrosis is not a pathologic entity but rather a descriptive term for a condition--necrosis of the renal papillae--that has various possible causes. The renal medulla and papillae are vulnerable to ischemic necrosis because of the peculiar arrangement of their blood supply and the hypertonic environment. The etiology of renal papillary necrosis includes diabetes, analgesic abuse or overuse, sickle cell disease, pyelonephritis, renal vein thrombosis, tuberculosis, and obstructive uropathy. Renal papillary necrosis has been diagnosed with the use of intravenous urography and ultrasonography, but contrast material-enhanced computed tomography (CT) may better depict a full range of typical features, including contrast material-filled clefts in the renal medulla, nonenhanced lesions surrounded by rings of excreted contrast material, and hyperattenuated medullary calcifications. In the presence of papillary sloughing, CT may depict hydronephrosis and filling defects in the renal pelvis or ureter, which also may contain calcifications. During healing, the epithelialized papillary tip appears blunted. Shrinkage of the kidney, a common sequela, also may be detected at CT. Multi-detector row CT depicts these and other features more clearly and directly than single-detector row CT, given the advantages of thinner sections and multiplanar reformation, and it may help identify the condition at an earlier stage, when effective treatment can reverse the ischemic process. Familiarity with the CT features of the condition therefore is useful for its successful diagnosis and management.