Squamosal Suture Synostosis: An Under-Recognized Phenomenon

Introduction: The squamosal suture (SQS) joins the temporal to the parietal bones bilaterally and is a poorly described site of craniosynostosis. SQS fusion is thought to occur as late as the fourth decade of life and beyond; however, we have incidentally noted its presence among our pediatric patients and hypothesize that it may occur earlier in life and more frequently than previously believed.

Methods: A retrospective review of imaging performed on pediatric patients was completed to identify patients with SQS synostosis. This included a review of clinical notes as well as computed tomography (CT) images obtained by our craniofacial clinic. Relevant patient data and imaging were reviewed.

Results: Forty-seven patients were identified with SQS synostosis, 21 were female (45%). Age at the time of radiographic diagnosis was 10.1 ± 8.4 years (range 17 days to 27 years). A majority of patients had bilateral SQS synostosis (57%), with a relatively even distribution of unilateral right (23%) versus left (19%). SQS was an isolated finding (no other suture involvement) in 15 patients (32%), all of whom were normocephalic and did not require surgical intervention. Thirty-two patients (68%) had concomitant craniosynostosis of other sutures, most commonly sagittal and coronal. Nine patients (19%) underwent surgery to correct cranial malformations-all these patients had multi-suture synostosis (P = 0.012). Twenty-seven patients (57%) had SQS synostosis diagnosed incidentally compared to 20 (43%) who were imaged with suspicion for synostosis. In those who were symptomatic, common findings included developmental delay, elevated intracranial pressure, hydrocephalus, seizures, and visual/hearing impairments. Ten patients (21%) were syndromic, the most frequent of which was Crouzon syndrome. No single pattern of calvarial malformation could be definitively described for SQS synostosis.

Conclusion: Given that most isolated SQS synostosis cases were normocephalic, asymptomatic, and discovered incidentally, it is likely that there are many cases of unidentified SQS synostosis. The significance of SQS synostosis is currently unclear, and warrants further investigation into this phenomenon, its natural course, and its potential presence in the spectrum of normal development.