Anomalies in cephalothoracopagus synotus twins and their implications for morphogenesis in conjoined twins

The anatomical features of a pair of female conjoined twins of the cephalothoracopagus type are described: the anterior face was well formed but the posterior face was cyclopean with a single ear canal. Visceral abnormalities included two shared hearts linked by an anastomotic arterial ring. The smaller of the hearts was univentricular with atrial situs ambiguus and anomalous pulmonary venous return, and was associated with two trilobed lungs. This, and the presence of a single spleen, suggested asplenia syndrome in one twin. The brains, orientated with respect to the notochordal axes, were joined only at the frontal poles. The abnormalities described in previous reports of twins of this type are reviewed and compared. In addition to alterations in body pattern due to conjoining, endodermal developmental defects and abnormal laterality appear to have been involved in the morphogenesis of this case.