INTRODUCTION

Unilateral coronal synostosis is the common appellation for premature, one-sided fusion of the frontoparietal suture, the most common cause of synostotic frontal plagiocephaly. The frontoparietal (“coronal”) suture is part of a continuous ring that extends around the calvaria and across the cranial base. This coronal ring is composed of the frontoparietal, frontosphenoid, and sphenoethmoid sutures. Growth in the coronal ring produces anterior enlargement of the calvaria and ventral expansion of the anterior cranial fossa. The sphenoethmoidal synchondrosis at the most medial aspect of the coronal ring has a major effect on antero-posterior growth of the cranial base and midface. Extension of the unilateral frontoparietal fusion into the frontosphenoidal suture has been reported, however, these reports are based on a few patients and plain radiography.

PURPOSE

The purpose of this study is to clarify the involvement of the basilar coronal ring in unilateral coronal synostosis, and to explore a possible correlation between the extent of sutural fusion and the degree of angulation in the cranial base.

MATERIALS AND METHODS

We retrospectively reviewed the radiographic record of 74 patients with unilateral coronal synostosis treated at our center between 1986 and 2001. Age, gender, and any possible syndromic association were recorded. Only patients with CT scans with axial images of acceptable quality were included. For each patient in the study, the axial images were carefully examined for evidence of premature fusion in the frontoparietal, frontosphenoidal, and sphenoethmoidal sutures. The extent of fusion was grossly quantified into quartiles (25%, 50%, etc.). The cranial base angulation was measured using the method of Lo et al. Analysis was performed using SAS statistical software.

RESULTS

Thirty-six patients were excluded because the CT scan was not available, was of poor quality, or had never been obtained (diagnosis by plain radiography) leaving 38 patients in the study (21 female, 17 males). Thirteen patients had a patent frontosphenoidal suture on the affected side by CT (Group I) and 25 patients had varying fusion along the lateral frontosphenoidal suture (Group II). The medial aspect of this suture was narrowed but consistently patent in all patients. The sphenoethmoidal suture was patent in all cases.

Mean age at time of CT scan study was 57.5 days in Group I (open frontosphenoidal suture), and 262.9 days in Group II (fused frontosphenoidal suture). The difference was statistically different (p=.001). In Group I, 77% of patients (10/13) had incomplete fusion of the frontoparietal suture, while in Group II only 20% (5/25) had incomplete fusion of the frontoparietal suture. The difference was statistically significant (p<0.05). All CT studies obtained before 3 months of age (11/11) showed a patent frontosphenoidal suture, while all patients in whom the CT study was done after 5 months of age (23/23) demonstrated partial frontosphenoidal fusion. Between 3 and 5 months, 2 patients had synostosis and 2 had an open frontospenoidal suture.

Mean cranial base angulation was 13.5 degrees in Group I and 15.7 degrees in Group II. The difference was not statistically significant (p=0.72). There was no statistically significant relationship between age at CT study and cranial base angulation.

CONCLUSIONS

Extension of the synostosis from the frontoparietal suture to the frontosphenoidal suture in the cranial base was not observed before 3 months of age, and was always present after 5 months. Thus, fusion along the coronal ring in UCS appears to progress and extend to the cranial base in early infancy. The sphenoethmoidal suture was patent in all patients and is not fused in UCS.
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