Severe hydronephrosis and severe renal cystic disease: ultrasonic differentiation.

End-stage renal cystic disease and severe hydronephrosis may reveal similar ultrasonographic findings. A "blind analysis" of 13 cases selected on the basis of smiliar extensive end-stage disease (little or no renal parenchyma visualized) was performed. The identification of a dilated renal pelvis was the most reliable ultrasonographic indicator of hydronephrosis. If the renal pelvis cannot be identified, renal cystic disease is the most likely diagnosis. All eight cases of hydronephrosis were correctly identified in this fashion. Four of five cases of severe cystic disease were correctly diagnosed. In one patient a peripelvic cyst was incorrectly interpreted as a dilated renal pelvis leading to the incorrect diagnosis of hydronephrosis. There may be ancillary signs that may help distinguish severe hydronephrosis from severe renal cystic disease. If these signs are not present, the only reliable criterion is whether the renal pelvis is dilated on careful examination of the renal sinus.