Unilateral megalencephaly: hamartoma or neoplasm?

The clinical and pathologic findings in three cases of unilateral megalencephaly, showing a spectrum of mild to severe involvement, are presented. The first case demonstrated an increase in neuronal size and mild gliosis and is contrasted with the second and third cases, which showed a progressive enlargement and bizarre appearance of neurons associated with an increase in number and size of astrocytes. The relationship of these cases to developmental and neoplastic disease in the brain is discussed.