Sonography of the fetal duplex kidney.

The sonographic features of the fetal duplex kidney are reviewed in five cases. Four cases had proven obstruction of either an upper (3 cases) or lower pole (1 case) moiety. Identification of two separate collecting systems may be difficult in utero. Therefore, the key to the sonographic diagnosis is recognition of asymmetric hydronephrosis between the dilated and nondilated moieties.