Hydronephrosis of the lower pole of the duplex kidney: another renal pseudotumor.

Obstruction and reflux occur fairly commonly in the duplex kidney. Although obstruction with attendant hydronephrosis is more frequently seen in the upper pole of a duplex system, a similar process involving the lower pole should be considered in the differential diagnosis of renal mass lesions. Four cases are described in which lower pole hydronephrosis simulated neoplasm.