Interhemispheric propagation of seizures in mesial temporal lobe epilepsy.

Objectives: 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.

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

Methods: 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.

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

Results: 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.

Conclusions: 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.