Benign external hydrocephalus in a boy with autosomal dominant microcephaly.

In a 3-month-old boy with microcephaly, magnetic resonance imaging (MRI) revealed accumulation of bifrontal extracerebral fluid. Because of the typical MRI findings and the disappearance of these findings later on, he was diagnosed as a case of benign external hydrocephalus. Both his mother and maternal grandmother had microcephaly, without neurological or dysmorphic manifestations. The pedigree is most consistent with an autosomal dominantly inherited microcephaly. This seems to be the first report of benign external hydrocephalus found in a patient with an autosomal dominant microcephaly.