Isolated Squamosal Synostosis: Defining the Phenotype

This study aims to characterize the clinical manifestations of isolated squamosal synostosis (ISS) and review the relevant published literature. Computed tomography imaging from 2008 to 2022 was reviewed to identify patients with ISS. Patients were reviewed for age at presentation, signs of intracranial pressure, and management. A systematic review was conducted of all studies on ISS from 1990 to 2023. Eighteen patients from our institution were included. Three unilateral cases were diagnosed at 1.4 ± 0.6 years. None had signs of intracranial hypertension nor required surgery. Of the 15 bilateral cases, 6 were completely fused and 9 were partially fused. Concern for intracranial hypertension was more frequent in patients with bilateral complete ISS (66%) than partial (22%). Vault remodeling was pursued in 5/6 patients with bilateral complete ISS and 4/9 patients with bilateral partial ISS. Systematic review yielded 13 cases of ISS. Four had unilateral ISS diagnosed at 5.2 ± 2.8 months. None had intracranial hypertension. Nine had bilateral ISS diagnosed at 31 ± 47.3 months. Three patients had signs of elevated intracranial pressure. ISS presentation seems to vary based on laterality. Unilateral ISS typically presents without intracranial hypertension. Bilateral ISS is often associated with intracranial hypertension, more so in cases of complete suture fusion. Bilateral ISS warrants close observation.