Hydranencephaly and maximal hydrocephalus: usefulness of electrophysiological studies for their differentiation.

The EEG was evaluated in three cases of hydranencephaly and two cases of maximal hydrocephalus, and the visual evoked potential was studied in one case each of hydranencephaly and maximal hydrocephalus. The EEG tracing of hydranencephaly typically showed a flat pattern in most bipolar derivations because of the differential amplification of the same activity from remote generators. However, the EEG of maximal hydrocephalus did not demonstrate a flat pattern in bipolar as well as referential derivation, and the activities were different from various electrodes in referential derivation. The visual evoked potential of maximal hydrocephalus showed a normal pattern, while that of hydranencephaly showed no response. Electrophysiological examinations (such as EEG and visual evoked potential) are useful for differentiation of hydranencephaly and maximal hydrocephalus in cases whose computed tomographic scans do not provide clear differentiation.