Impact of the Extent of Suture Fusion and Minor Suture Involvement on Craniofacial Morphology in Unilateral Lambdoid Synostosis

Introduction: Unilateral lambdoid synostosis (ULS) is the rarest form of single-suture craniosynostosis, producing characteristic posterior cranial asymmetry. Although typically described as an isolated defect, recent studies suggest that adjacent minor sutures may also exhibit premature fusion. The purpose of this study is to evaluate the degree of suture fusion and frequency and impact of minor suture involvement in patients with ULS. Methods: A retrospective review of 50 patients with ULS computed tomography (CT) scans was performed to assess the degree of lambdoid suture fusion (complete, upper 2/3, lower 2/3) and minor suture involvement. Three-dimensional CT scans were used to determine the impact on craniometric measurements. Results: The lambdoid suture fusion distribution was 36% complete, 40% upper 2/3, and 24% lower 2/3. Minor suture synostosis was found in 16% of patients with ULS. The minor sutures involved included 8% with occipitomastoid suture synostosis and 12% with posterior intraoccipital suture synostosis. All patients demonstrated cranial asymmetry, ipsilateral posterior fossa deflection, ipsilateral inferior skull base, and significantly anterior ipsilateral deviation of the petrous ridge, external acoustic meatus, midface, and articular fossa. No significant difference was found in any measurement based on the degree of suture fusion or minor suture involvement. Conclusions: The degree of lambdoid suture fusion and minor suture involvement did not significantly impact the degree of craniofacial malformations in ULS. Minor suture involvement was observed in 16% of patients, with posterior intraoccipital suture synostosis being most common.