The child with unilateral lambdoid synostosis has a thick ridge over the fused suture, with compensatory contralateral parietal and frontal bossing 1). There is an ipsilateral occipitomastoid bulge, with a posteroinferior displacement of the ipsilateral ear. These characteristics are opposite to the findings in the children with deformational plagiocephaly. In the view from above, the shape of the head will be trapezoid in lambdoid synostosis and parallelogram in deformational plagiocephaly. A 3D CT will confirm the diagnosis. Torticollis is most commonly associated with deformational plagiocephaly. Chiari malformation can be present with lambdoid synostosis.
1)
Huang MH, Gruss JS, Clarren SK, Mouradian WE, Cunningham ML, Roberts TS, Loeser JD, Cornell CJ. The differential diagnosis of posterior plagiocephaly: true lambdoid synostosis versus positional molding. Plast Reconstr Surg. 1996 Oct;98(5):765-74; discussion 775-6. doi: 10.1097/00006534-199610000-00001. PMID: 8823012.