Abstracts

Rationale: We reported very high frequency activities of 1000-2500 Hz in highly localized cortical areas of patients with neocortical epilepsy recorded by subdural electrodes, and named these activities very high frequency oscillations (VHFO) (Usui et al., Clin Neurophysiol. in press). In this study, the clinical significance of VHFO was investigated. Methods: Ten patients with intractable focal epilepsy (eight with neocortical epilepsy, and two with medial temporal lobe epilepsy) were studied. All patients underwent intracranial EEG monitoring. EEG recording with a sampling rate of 10 kHz was conducted. The presence or absence of VHFO, the location of VHFO, postoperative seizure outcome, and pathology were analyzed. Results: In five patients with neocortical epilepsy and one with medial temporal lobe epilepsy, VHFO of 1000-2500 Hz was detected in highly localized areas. In all six patients with VHFO, the areas with VHFO were included in the seizure onset zone and irritative zone. In four of five neocortical epilepsy patients, surgical resection included the areas with VHFO. Three of these four patients have been seizure-free, and the remaining patient had simple partial seizures. In the fifth patient with VHFO, the area with VHFO was located over primary somatosensory area and was not included in the resection. She has also been seizure-free. Surgical resection was not performed in the medial temporal lobe epilepsy patient with VHFO. VHFO was not detected in the remaining three patients with neocortical epilepsy and one with medial temporal lobe epilepsy. In three neocortical epilepsy patients without VHFO, postoperative seizure outcome was favorable in one and unfavorable in the remaining two. One medial temporal lobe epilepsy patient without VHFO had an unfavorable outcome. Histology revealed cortical dysplasia in all five patients with VHFO. In three neocortical epilepsy patients without VHFO, cortical dysplasia was detected in two. Hippocampal sclerosis was detected in one patient with medial temporal lobe epilepsy. Conclusions: The presence of VHFO may be related to favorable seizure outcome. Further studies are necessary to clarify the clinical significance of VHFO.