The open opercular sign: diagnosis and significance.

Four children with varying clinical manifestations, but with the unifying feature of severe developmental delay, had bilateral enlargement of the sylvian fissure confirmed by magnetic resonance imaging (MRI). Subsequently, we examined 125 consecutive MRI scans of the heads of pediatric patients, looking for this insular exposure, and did not find it. Pathological correlation in 1 child revealed arhinencephaly and abnormal gyral formation; another is known to have migrational abnormalities. We suggest that the open operculum is a sign of arrested development and is associated with other anomalies and a poor prognosis.