Ischiopagus tetrapus twins: urological aspects of separation and 10-year followup.

Conjoined twins occur once in 50,000 births. Only 6% of conjoined twins are of the ischiopagus type in which the twins are joined symmetrically at the pelvis and fusion begins at the level of the common umbilicus. The longitudinal axis extends in a straight line in opposite directions and the genitourinary and gastrointestinal tracts are shared. Tetrapus is a subtype in which all 4 lower extremities are present and oriented at right angles to the axis of the common trunk. Two sets of female ischiopagus tetrapus twins were born in 1977 and successfully separated at the St. Louis Children's Hospital in the following year. We describe the genitourinary and associated anomalies, surgical separation and long-term urological followup of these 2 sets of ischiopagus tetrapus twins.