[Localized fast rhythms in EEG tracings following surgery for intracranial meningioma]

Forty-six patients were followed up after removal of an intracranial meningioma. Nine of the 46 patients in their 3rd month postoperative EEG had localised fast rhythms which remained stable. The fast rhythms appeared in small 20-25 Hz and 20-40 microV bursts; they were localised over the craniotomy flap as shown by the control X-ray of the sites of the electrodes; they were unaffected by eye-opening and slightly reduced by fist-clenching. These fast rhythms were sometimes mixed with sharp waves and theta activity and seemed to be equivalent to the 'breach rhythm' described first by Fischgold et al. (1952) and then by Cobb et al. (1979). In our study, these rhythms were more frequently observed in patients with an olfactory or sphenoidal meningioma, in patients with pre-operative seizure and in patients with an extensive post-operative intracranial atrophy (as shown by the scanner). On the other hand, incomplete removal or recurrence of the tumour or post-operative epilepsy did not seem to play a role in the appearance of these rhythms.