Abstracts

Rationale: Intracranial recordings are used to define the epileptogenic region in complex cases with insufficient or inconsistent localizing information from non-invasive studies, and particularly in non-lesional cases to prove uniregional seizure origin and to plan surgical interventions. The type of intracranial investigation greatly differs between centers without universal agreement as to the optimal diagnostic procedure. We here retrospectively analyzed outcomes of subdural and depth electrode recordings at the Freiburg Epilepsy Center to compare the diagnostic yield of these approaches.

Methods: 443 consecutive patients (347 with MR-lesion, 96 non-lesional) undergoing intracranial presurgical evaluation were analyzed using electronic charts and information from MR imaging and intracranial electrophysiology. 147 patients underwent purely subdural evaluation, 160 patients depth electrode recordings, and 136 a combined approach. Patients were analyzed as to whether (1) the epileptogenic region could be identified with certainty or approximately, (2) surgery was recommended, and (3) how the brain region of implantation influenced these results.

Results: (1) In lesional epilepsy, in 63% of patients undergoing subdural recordings, 69% of patients with depth recordings, and 61% of patients with combined recordings were considered to have a clear definition of the seizure onset zone. Rates were lower in non-lesional epilepsy, with a clear seizure onset zone in 54% of patients undergoing subdural recordings, 55% of patients with depth recordings, and 55% of patients with combined recordings were considered to have a clear definition of the seizure onset zone.

(2) In lesional epilepsy, 86% of patients undergoing subdural recordings, 64% of patients with depth recordings, and 83% of patients with combined recordings proceeded to surgery with a mean Engel I outcome of 60.8 %. In non-lesional epilepsy, 63% of patients undergoing subdural recordings, 57% of patients with depth recordings, and 55% of patients with combined recordings proceeded to surgery with a mean Engel I outcome of 54.2%.

(3) In both, temporal and frontal implantations of lesional patients, the rate of patients proceeding to surgery was higher following subdural recordings than in those undergoing depth recordings only, although the proportion of patients with clearly identified channels with seizure onset was at least as high with depth electrodes.

Conclusions: In both, non-lesional and lesional patients subdural and depth electrode recordings showed high rates of succesful identification of the seizure onset zone. In subdural recordings, patients in whom seizure onset was defined only approximately, more frequently proceeded to surgery. Resulting proportions of operated patients obtaining complete seizure control was almost as high in non-lesional cases as in patients with imaging-defined lesions. Either implantation strategy thus proved valid and rewarding in properly selected patients.

Funding: Please list any funding that was received in support of this abstract.