Hypertrophy of the cerebral white matter in hemimegalencephaly.

We morphometrically measured the cut surface of the cerebral hemisphere and localized epidermal growth factor (EGF)-like immunoreactivity in 4 patients with hemimegalencephaly. On the affected side, the area of cerebral white matter was more than twice as large as that on the unaffected side, while the area of the cerebral cortex on the affected side was relatively small. EGF-like immunoreactivity was demonstrated in cortical neurons (4 of 4 patients) and glial cells (3 of 4 patients), notably in astrocytes. Significant enlargement of the cerebral white matter compared to the cerebral cortex and the expression of EGF-like molecules in astrocytes suggest excessive proliferation in the white matter with hemimegalencephaly and the possible relevance of EGF to these events.