Hemorrhage in development of the face.

Focal hemorrhages, early in embryogenesis, may play a significant part in the pathogenesis of specific malformations. Animal models of hemifacial microsomia and thalidomide-induced otomandibular dysostosis are described; the causal mechanism of malformation appeared to be closely related to the formation of a hematoma at the time of development of the stapedial arterial systems. The effects of the hematoma on morphogenesis are described, and the changes observed in the animal models compared with similar anomalies in man.