Use of frameless stereotaxy with location of electroencephalographic electrodes on three-dimensional computed tomographic images in epilepsy surgery.

Epileptiform activity corresponding to structural lesions was identified by three-dimensional (3D) imaging using computed tomographic (CT) scan data concurrently with scalp EEG electrodes. The electrodes, placed according to the international 10-20 system, were used to record interictal and ictal epileptogenic foci in eight patients. Electrodes placed where marked or moderate epileptiform activity was detected were replaced with markers detectable on CT. Scans with these markers on the skin were obtained and the data transferred to a 3D imaging system, and correlated with underlying cerebral structures. The reformatted images were used to assess the relation among intracranial lesions, brain surface structures, and epileptogenic zones depicted by the markers. The images help the surgeon plan a craniotomy with enough space for both lesionectomy and resection of the epileptogenic zone. In the central regions where crucial motor functions are located, the markers indicate the central fissure or postcentral gyrus. An intraoperative 3D frameless stereotactic pointing device helps in directing further examination of the epileptogenic zone. This system improves on the precision available through intraoperative electrocorticographic recording in the extratemporal lobes, thus avoiding only approximate excision of lesion and epileptogenic zone and enabling the neurosurgeon to perform epilepsy surgery with greater confidence.