Extreme microcephaly with agyria-pachygyria, partial agenesis of the corpus callosum, and pontocerebellar dysplasia.

A 1-year-old boy with extreme microcephaly and a complex brain malformation is reported. Magnetic resonance imaging revealed an abnormal gyral pattern with features of the agyria-pachygyria spectrum, partial agenesis of the corpus callosum, severely hypoplastic posterior cerebellar vermis, and an abnormal foliation pattern of the cerebellar hemispheres associated with a flat and wide isthmus and pons. Although this phenotype shares some features with malformations classified as microcephaly with a simplified gyral pattern, microlissencephaly, or lissencephaly with cerebellar hypoplasia, none of the several subgroups of these categories are identical to the cerebral dysgenesis found in this patient.