Craniofacial microsomia in a parasite of a heteropagus conjoined twin: a clinical and histopathologic evaluation.

This report evaluates a rare case of craniofacial microsomia in a partially developed, malformed heteropagus conjoined twin. In this instance, several major components of the craniofacial complex were involved: bones, cartilage, teeth, salivary glands, auditory apparatus, cerebrum, cranial nerves, and ocular neuroepithelium. In addition, cervical vertebrae and appendicular long bones were markedly affected. To date, the underlying disorder (whether genetic, metabolic, or environmental) responsible for the development of this congenital malformation is not fully understood. Our clinical and pathologic examinations tend to suggest that an apparent lack of an adequate arterial blood supply to the growing embryo could have contributed to the elaboration of this complex syndrome. The fact that the parasite's blood supply relied mainly upon a single, medium-sized artery (1.5 mm in diameter) could have brought about local ischemic milieus during the critical phases of embryogenesis; hence, impeding the preprogrammed migration of neural crest cells to their end targets in the upper branchial arches. In such a case, the normal sequence of cell differentiation is damaged, which in turn imposes a severe impact on the morphogenesis of the various tissues composing the craniofacial complex.