Cranial deformation in craniosynostosis. A new explanation.

Skull growth after premature fusion of a single suture was described by Virchow in 1851. He observed that growth was restricted in a plane perpendicular to a fused suture. However, he failed to predict the compensatory growth patterns that produce many of the deformities recognized as features of individual craniosynostosis syndromes. The deformities resulting from premature closure of a coronal, sagittal, metopic, or lambdoid suture can be predicted by the following observations: (1) cranial vault bones that are prematurely fused act as a single bone plate with decreased growth potential; (2) asymmetrical bone deposition occurs mainly at perimeter sutures, with increased bone deposition directed away from the bone plate; (3) sutures adjacent to the stenotic suture compensate in growth more than those sutures not contiguous with the closed suture; and (4) enhanced bone deposition occurs along both sides of a nonperimeter suture that is a continuation of the prematurely closed suture. These four rules were derived by critically examining the clinical deformities observed with each form of craniosynostosis. These rules assume that cranial sutures have the capacity to compensate by depositing bone asymmetrically along their edges. Unequal growth patterns have been demonstrated in the frontonasal suture of rabbits by Selman and Sarnat. In addition, unequal bone deposition has also been demonstrated along the parieto-interparietal suture in albino rats by Baer. Human studies to determine if asymmetrical bone deposition actively occurs along cranial vault sutures in response to a stenotic suture have not been performed, however. It is also unclear whether these four guidelines apply to cranial base abnormalities observed with craniosynostosis. As new radiologic techniques develop to define the configuration of the skull in intricate detail, a skull pattern of growth explaining the pathogenesis of all deformities created by premature fusion of a cranial vault suture may become apparent.