Distinguishing Craniomorphometric Characteristics of Unilateral Lambdoid Craniosynostosis.

Abstract

Unilateral lambdoid synostosis (ULS) represents the rarest form of single suture nonsyndromic craniosynostosis. Differentiating between posterior deformational plagiocephaly (DP) and ULS has been difficult due to overlapping clinical findings. Past analyses have been limited by sample size. This study was undertaken to clarify anatomical features of ULS. A multiinstitution study was undertaken, analyzing CT imaging from patients with documented ULS to determine clinical and pathological characteristics. Similar analyses were performed on DP patients to differentiate the 2 conditions. Twenty-seven ULS patient scans and 10 DP scans were included. For ULS patients mean age was 6.6 months, majority male (75%), and majority left-sided ULS (71%). The synostosed side ear was anteriorly displaced in 100% of ULS patients, mean difference of 9.6° (P < 0.001), and inferiorly in 96.3% of patients, mean difference of 4.4 mm, relative to the nonsynostosed side. The posterior fossa deflection (PFD) was deviated 5.9° toward the synostosed side relative to the anterior midline. In DP, there was no significant difference between sides in EAC measurements. The PFD and EAC displacements were significantly smaller in DP relative to ULS (P < 0.001 for each). An ipsilateral mastoid bulge was found in 100% of ULS and 0% of DP on CT imaging. Contrary to some previously published findings, the ear is more anteriorly displaced ipsilateral to the fused lambdoid suture in 100% of ULS patients. Ear position alone is not a reliable indicator to differentiate between DP and ULS. A mastoid bulge is a more reliable indicator of ULS.