The deformed petrous bone: a new plain film sign of premature lambdoid synostosis.

Towne-view skull radiographs of 38 infants with unilateral lambdoid synostosis were reviewed. The diagnosis of lambdoid synostosis was based on other plain film findings, CT findings, or clinical examination. All patients had deformity of the ipsilateral petrous bone, presumably because of pressure caused by redirected brain growth. Specific changes included flattening of the petrous ridge and depression of the roof of the mastoid portion of the petrous bone and adjacent structures such as the semicircular canals. Flattening of the petrous ridge and depression of the roof of the mastoid portion of the petrous bone are useful signs of lambdoid synostosis when sutural closure has produced sutural indistinctness rather than sclerosis.