Ultrasonographic unilateral hydronephrosis with bladder outlet obstruction.

Renal ultrasonography plays an important role in the evaluation of azotemic patients. Knowledge of its limitations is crucial for the proper evaluation of obstructive uropathy. Two cases are presented in which screening ultrasonography detected unilateral hydronephrosis despite lower urinary tract obstruction. Both patients had markedly asymmetrical renal function, with the hydronephrosis found in the better functioning kidney. The importance of searching for asymmetry of renal function in the azotemic patient with atypical ultrasonogram findings is emphasized. Other clinical factors which would heighten suspicion for obstructive uropathy and lead to further investigation despite a minimally abnormal or even normal renal ultrasonogram are also discussed.