Hydranencephaly versus maximal hydrocephalus: an important clinical distinction.

To define better the syndromes of hydranencephaly and maximal hydrocephalus, we followed 10 neonates demonstrating (by computerized tomography) virtual absence of the cerebral substance with serial computerized tomographic (CT) scans, electroencephalograms (EEGs), and developmental evaluations. The follow-up period ranged from 4 to 23 months. Two well-defined syndromes emerged. Five patients showed absence of cortical activity on EEG and a CT picture of minimal occipital brain parenchyma connected by a thin bridge of tissue to intact basal ganglia. These patients were shunted and showed no improvement with time, either neurologically or radiologically. Five patients showed minimal frontal cerebral mantle on CT and the presence of electrical activity on EEG. These patients required bilateral shunts to control head size and showed remarkable progress with time. Serial CT scans demonstrated the appearance of considerable brain substance, and neurological development was either normal or slightly delayed. We believe that the former pattern of only minimal occipital brain and absent EEG activity defines true hydranencephaly, whereas the presence of small amounts of frontal brain tissue associated with EEG activity seems to represent maximal hydrocephalus. The differences in CT pattern, EEG, and clinical progress all suggest a different pathophysiology for these two conditions. (Neurosurgery, 6: 35--38, 1980).