Acardius anceps with evidence of intrauterine vascular occlusion: report of a case and discussion of the pathogenesis.

An acardiac anomaly (holoacardius anceps) showed advanced development of the head and lower body parts in the absence of all thoracic and upper abdominal viscera. Large vascular anastomoses in the vertebral canal formed the only blood supply to the head. The two-vessel umbilical cord of the acardius contained calcified mural thrombi in both vessels. Severe fetal hydrops resulted in an exceptionally large birth weight of 3720 g. Fibroblasts from the acardius showed chromosomal mosaicism. The surviving co-twin was remarkable for a widely patent ductus arteriosus, unilateral multicystic renal dysplasia, and a normal chromosome complement. The circumscribed absence of organ development in the thorax and upper abdomen of the acardius and the vascular anatomy with thrombosis of the umbilical vessels suggest that an occlusion of thoracic and abdominal vessels was significant in the development of this acardiac malformation and should be considered as a possible pathogenetic mechanism in similar cases of acardia.