Metopic Synostosis: Defining the Temporal Sequence of Normal Suture Fusion and Differentiating It from Synostosis on the Basis of Computed Tomography Images

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Abstract
Only the metopic suture normally fuses during early childhood; all other cranial sutures normally fuse much later in life. Despite this, metopic synostosis is one of the least common forms of craniosynostosis. The temporal sequence of normal physiologic metopic suture fusion remains undefined and controversial. Therefore, diagnosis of metopic synostosis on the basis of computed tomography images alone can prove misleading. The present study sought to determine the normal sequence of metopic suture fusion and characterize both endocranial and ectocranial suture morphology. An analysis of computed tomography scans of 76 trauma patients, ranging in age from 10 days to 18 months, provided normative craniofacial data that could be compared to similar data obtained from the preoperative computed tomography scans of 30 patients who had undergone surgical treatment for metopic synostosis. Metopic suture fusion was complete by 6 to 8 months in all nonsynostotic patients, with initiation of suture fusion evident as early as 3 months of age. Fusion was found to commence at the nasion, proceed superiorly in progressive fashion, and conclude at the anterior fontanelle. Although an endocranial ridge was not commonly seen in synostotic patients, an endocranial metopic notch was virtually diagnostic of premature suture fusion and was seen in 93 percent of synostotic patients. A metopic notch was not seen in any nonsynostotic patient. The morphologic and normative craniofacial data presented permit diagnosis of metopic synostosis based on computed tomography images obtained beyond the normal fusion period.