Basal plate dysplasia presenting as a hamartoma of the pontine tegmentum

A child with an intractable, nonfocal seizure disorder, progressive lethargy, and psychomotor retardation had a malformation involving rhombencephalic structures deriving from the embryonic basal plate. Its principal component was a mature neuroepithelial hamartomatous mass arising from the pontine tegmentum. Diencephalic, metencephalic, and myelencephalic derivatives of the alar plate were remarkably spared. To our knowledge, the morbid anatomy and embryopathology of this central nervous system malformation has not been previously described.