Craniosynostosis with associated cranial base anomalies: a morphologic and histologic study of affected like-sexed twins.

A set of like-sexed male twins with the same malformation syndrome and exhibiting identical anomalous alterations of the craniofacial complex were studied in detail. The right and left coronal and left lamboidal sutures were prematurely synostosed in both specimens. The cranial base exhibited a mediolateral asymmetry, with the right half larger than the left. The occipital bone demonstrated the greatest abnormality, including bilateral clefting of the basioccipital component and alterations in the size and shape of the exoccipital bone. In lateral view, the cranial base was flattened and the ventral flexure occurred between the two components of the basioccipital. The odontoid process of the second cervical vertebra was rotated anteroinferiorly and formed part of the cranial floor. Histologically, the bilateral clefts of the basioccipital bone were united by fibrous connective tissue, and the central area of union contained chondroid-like bone. The cartilaginous spheno-occipital synchondrosis and the epiphyseal cartilage of the finger demonstrated similar dystrophic alterations. The brain was normal but exhibited external cerebral deformation secondary to aberrant skull shape.