Congenital absence of the atlas posterior arch. A case report.

A report of a healthy young adult woman with non-pathological congenital absence of the lateral and posterior parts of the atlas is presented. This occurred in association with a steep mandibular plane angle and an extremely obtuse gonial angle. Similar facial features are common in females with hypoplastic dorsal arches, and this case illustrates the intimate developmental association between the upper part of the cervical spine and the craniofacial complex.