The Electroencephalogram in Intracranial Aneurysms

Abstract

Multiple eegs. were taken on 42 cases of proved aneurysms and in 53 cases of spontaneous subarachnoid hemorrhage with hemiparesis or cranial nerve palsies. Recordings were taken as soon after the history of rupture of the aneurysm as possible, and subsequent serial records were made in many instances. The eeg. picture in the proved and unproved aneurysms was identical. In 4 proved aneurysms there was no history of rupture. In all instances the initial changes in the eegs. within the first 1-2 weeks subsequent to rupture were: ipsilateral decrease in amplitude; ipsilateral delta focus; and ipsilateral slowing of the alpha activity. These 3 factors were present alone or in combination. Of these, the voltage decrease was the most constant factor. With the passage of time, the initial amplitude reduction might be replaced by a subsequent increase, usually in 2-4 weeks. The end result in all cases was substantial decrease, although the increased phase might reappear one or more times. The permanent voltage reduction usually appeared by the 3d month subsequent to rupture. The voltage changes were most notable in the temporal and occipital areas. 3 of 4 unruptured aneurysms showed ipsilateral amplitude decrease, the 4th showed increase. In subsequent weeks following rupture an initial eeg. might appear to be inconclusive for the purpose of lateralization. Serial records taken over the next 7-10 days will usually resolve this difficulty. Evidence is given that delta foci usually indicate one or more of the following: intracerebral hematoma; vasospasm and/or thrombosis of the major vessel involved in the aneurysm; and aneurysm of the middle cerebral, anterior cerebral or anterior communicating arteries. Persistence of a delta focus beyond 3 weeks subsequent to rupture and without operative interference usually indicates an intracerebral hematoma. The delta foci are most commonly seen in the temporal and frontal areas. Using the above criteria, the eeg. definitely can lateralize an intracranial aneurysm or hematoma. Although our studies are incomplete, there is some indication that the eeg. may aid in localization.