Department of Pathology, U.T. Southwestern Medical Center, Dallas 75235-9072, USA.
A case of craniopagus parasiticus is described in which the parasitic twin is more fully developed anatomically than in any of the previous reports. Somatic and placental vascular anastomoses between the twins and hypoplasia of the umbilical cord of the parasite were also observed. These findings support the hypothesis that craniopagus parasiticus results from compromise of the blood supply to one of a pair of craniopagus conjoined twins.