Dicephalus conjoined twins: a historical review with emphasis on viability.

Dicephalus conjoined twins (2 heads on 1 body) form a distinct subgroup. They are often stillborn because of cardiopulmonary malformations. This article describes 17 historical cases with particular emphasis on viability. There are reliable reports of unseparated dicephali reaching maturity; 1 pair (the Tocci brothers) reached at least 34 years of age. In the absence of concomitant cardiac, pulmonary, and intestinal malformations, dicephalus conjoined twins may well attain adulthood. This appears to be unrelated to whether they have 4 (dicephalus tetrabrachius) or 3 (dicephalus tribrachius) arms at birth.