Role of Subdural Interhemispheric Electrodes in Presurgical Evaluation of Epilepsy Patients

Surgery is a well-established and safe treatment option for focal drug resistant epilepsy. However, difficulties are often encountered in diagnosing mesial cortical lesions. The aim of this study was to evaluate the usefulness and overall complication rate of subdural interhemispheric electrodes (IHEs) as part of an invasive presurgical evaluation of epilepsy patients.

A total of 100 patients who underwent implantation of subdural IHE were included in the study. Data on surgical complications, subdural electrodes and contacts, benefits of invasive electroencephalography recording, and final seizure outcome were collected and analyzed.

A total of 343 subdural strip electrodes with a total of 1470 contacts were implanted. There were 6 perioperative/postoperative complications, none of them leading to a permanent neurologic deficit. An increased number of IHE (P = 0.005) and IHE-contacts (P = 0.03) also increased the rate of focus detection, while not significantly changing complication rate (P = 0.26). Two benefits of IHE (focus detection of interhemispheric lesions and mapping) in extratemporal resections were significantly associated with excellent seizure outcome (ILEA1) (P = 0.03, respectively P < 0.001). Other features associated with excellent seizure outcome are pure resections (w/o multiple subpial transection, P = 0.006), specific histology (P < 0.001), and a visible magnetic resonance imaging lesion (P = 0.002).

Implantation of IHE for the preoperative evaluation of epilepsy patients is an established surgical procedure with an acceptable complication profile. The benefits delivered from IHE can positively influence final seizure outcome in the challenging group of extratemporal resections due to interhemispheric lesions. Thus IHEs demonstrate a useful diagnostic utility for the presurgical evaluation of selected epilepsy patients.