Interhemispheric propagation of seizures in mesial temporal lobe epilepsy

To investigate interhemispheric propagation of mesial temporal lobe epilepsy seizures in patients undergoing long-term video-EEG monitoring with combined scalp and foramen ovale electrodes.

To reveal possible interhemispheric propagation patterns in mesial temporal lobe epilepsy, to improve presurgical evaluation of temporal epileptic patients.

Sixty-five seizures from 20 patients were analyzed. We defined two contralateral seizure propagation patterns: Type I for those seizures that spread to the contralateral foramen ovale electrodes earlier than to the contralateral scalp electrodes, and type II for the opposite.

Twenty drug resistant epileptic patients were investigated in frame of their presurgical evaluation.

The majority of seizures (80%) were classified as type I. Inter-foramen ovale electrode propagation time was significantly shorter for type I compared to type II seizures. Ninety percent of patients had either type I or type II seizures only. Patients with type I seizures significantly more often had mesiotemporal structural alterations evident on magnetic resonance imaging scans, and became more often seizure-free after surgery compared to patients with type II seizures whose surgical outcome was less favorable or surgery could not be indicated because of independent bilateral ictal seizure-onset.

The two types of contralateral propagation patterns we are describing seem to represent two subtypes of mesial temporal lobe epilepsy with different morphological and prognostic features. The predominance of type I over type II seizures together with shorter propagation times for type I seizures indicate a role of a more direct and dominant interhemispheric pathway in mesial temporal lobe epilepsy.