Stereotactic Electroencephalography in Patients with Drug-resistant Epilepsy

Stereotactic electroencephalography (SEEG) is an important method for invasive presurgical exploration of candidates for epilepsy surgery by means of stereotactic implantation of intracerebral electrodes without craniotomy. Implantations of intracerebral electrodes through craniotomy in drug-resistant epileptic patients have been performed in Bulgaria in the 1980s, but no further development of epilepsy surgery followed. The aim of our study is to present the first Bulgarian series of patients with drug-resistant epilepsy explored by SEEG. Our study included 53 patients with drug-resistant epilepsy explored by SEEG. Stereotactic Leksell frame, stereotactic software for avascular trajectory planning and depth electrodes with diameter of 0.8 mm and 8–18 contacts were used in all patients. Subsequently, long-term video-SEEG monitoring of various duration was performed and registered interictal and ictal EEG activity in order to evaluate the putative epileptogenic zone. Fifty-three patients were explored by 62 SEEGs because one patient underwent three SEEG procedures and seven patients – two SEEG procedures. We implanted 753 electrodes in these 62 SEEGs (mean: 12 electrodes per exploration; range: 5–20 electrodes). The mean age in our cohort was 23.6 years (4–60 years). The main indication for SEEG was MRI-negative epilepsy (20 patients). Focal cortical dysplasia was found in 17 cases, and hippocampal sclerosis in 8 cases. Surgical intervention was done in 48 patients (91%). Surgical resection of the epileptogenic zone (EZ) as defined by the SEEG was performed in 27 patients; radiofrequency stereotactic thermocoagulation (RFTC) on selected electrode contacts was applied in seven patients, and both procedures (i.e. RFTC followed by resective surgery) were performed on 14 patients. Full seizure control (Engel class I) was achieved in 28 patients (58.3%) and significant improvement – in 17 patients (35.4%). Three patients (6.2%) had no effect from surgery. No complications were observed in our series of 62 SEEGs. SEEG is a major tool for the determination of the EZ in patients with drug-resistant epilepsy who are candidates for epilepsy surgery, including MRI-negative cases or such without congruent data from the clinical, neurophysiological and neuroimaging perspectives. SEEG is a low-risk invasive diagnostic and even a therapeutic method when performed by experienced epilepsy surgery team.