Osseous Convexity at the Anterior Fontanelle: A Presentation of Metopic Fusion?

Background: Craniosynostosis, or a premature fusion of 1 or more cranial vault sutures, results in characteristic head shape deformities. In previous reports, an osseous prominence at the anterior fontanelle has been suggestive of adjacent suture fusion and local elevation in intracranial pressure (ICP). This prominence has been termed the "volcano" sign, and has been described in the anterior fusion of the sagittal suture and serves as an indication for surgery. Methods: Two patients presented for head shape evaluation with mild metopic ridging and anterior fontanellar osseous convexities consistent with the volcano sign. Low-dose computed tomography imaging was performed in both patients due to concern for underlying craniosynostosis with elevated locoregional ICP. Results: In both patients, imaging was significant for a localized, superior forehead metopic fusion, as well as a bony, convex prominence at the site of the ossified anterior fontanelle. There were no other clinical or radiologic signs or symptoms to suggest elevated ICP. Surgery was not indicated in either patient. Conclusions: Here the authors present 2 patients with osseous convexities at the site of the closed anterior fontanelle without signs or symptoms of elevated ICP, or classic signs of metopic synostosis. The authors hypothesize that this pattern may be due to a form of mechanically induced premature fusion of a normal metopic suture that is focused superiorly at the bregma, with minimal resultant restriction of overall skull growth. This is in contrast to metopic synostosis, which primarily has a sutural pathology and leads to characteristic findings of hypotelorism and trigonocephaly.

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