The electroencephalogram in cases of subdural hematoma and hydroma

Abstract

The EEG findings in 32 patients with subdural effusion are reported. Twenty-four of these were unilateral subdural hematomas, 4 were bilateral hematomas, and 4 were unilateral hydromas. The EEG abnormalities were of two types: (A) suppression of alpha activity on the side of the lesion in 13 of the 24 unilateral hematomas and in 2 of the unilateral hydromas; (B) slow wave activity of either low or increased voltage, which occurred in 11 of the unilateral lesions and 3 of the bilateral ones. The slow activity characteristically was irregular, from 1 to 5 per sec. and non-paroxysmal in character. Suppression of alpha activity was a specific effect and was best demonstrated between electrodes closely spaced in an anterior-posterior line. In 5 anteriorly placed hematomas suppression of alpha activity was encountered. Spiking did not occur; and sharp waves were rare. The EEG gave a correct lateralization in 75 per cent of the cases and a correct localization on the side indicated in 47 per cent. The EEG did not distinguish between unilateral and bilateral subdural accumulations. Only 4 per cent of the group showed normal EEG's with subdural hematoms; whereas EEG's from 2 of the 4 patients with unilateral hydromas were normal. A total figure of 90 per cent abnormality was encountered in the entire group. The data reported agree very well with other reviews and cases reports in the literature.