Involvement of the Basilar Coronal Ring in Unilateral Coronal Synostosis

Abstract

Unilateral coronal synostosis denotes one-sided premature fusion of the frontoparietal suture. However, this is only one component of the coronal hemi-ring that includes the contiguous frontoparietal, frontosphenoidal, and frontoethmoidal sutures. Possible fusion of the basilar sutures in unilateral coronal synostosis is poorly documented. The authors retrospectively reviewed the radiographic records of 91 patients with unilateral coronal synostosis who were evaluated in their unit between 1986 and 2003. Fifty-one computed tomography scans were of sufficient quality to adequately assess the basilar sutures. Each suture in the coronal hemi-ring (frontoparietal, frontosphenoid, and sphenoethmoid) was assessed on axial images for evidence of synostosis, extent and location of fusion, and cranial base angulation. The data were analyzed using SAS statistical software (SAS, Cary, N.C.). One frontoparietal ("coronal") suture was fused in all 50 patients. Synostosis was incomplete in 19 patients; specifically, the superior and inferior portions of the frontoparietal suture were patent. Fourteen of the 19 scans showing partial frontoparietal fusion were in infants less than 5 months of age. Scans were grouped according to extent of fusion in the basilar coronal hemi-ring: group I (n = 15), the frontosphenoidal suture was open on the affected side, whereas in group II (n = 36), there was variable synostosis in the lateral portion of the ipsilateral frontosphenoidal suture. Patients in group I were significantly younger than those in group II at the time of computed tomographic study (p < 0.001). Furthermore, group I patients were more likely to have incomplete frontoparietal fusion, as compared with group II (p < 0.001). The frontosphenoidal suture was patent in 100 percent of patients younger than 3 months, in 43 percent of those between 3 and 5 months old, and in 0 percent of patients older than 5 months at the time the scan was obtained. There was also a trend toward a larger cranial base angulation in group II, although this difference was not significant (p = 0.33). Seven patients were syndromic; however, their mean age (207 days) at the time of computed tomography was not statistically different from that of patients without a detectable mutation (188 days), nor did the cranial base angulation differ in this subgroup. The authors conclude that unilateral coronal fusion begins in the middle of the frontoparietal suture and extends superiorly and inferiorly. There also is age-dependent, progressive involvement of the lateral frontosphenoidal suture between 3 and 5 months of age. Nevertheless, synostotic extension into the basilar coronal hemi-ring is not associated with increased cranial base angulation.