Abstracts

RATIONALE: Epileptogenic zones (EZ) which include part of the temporal lobe structures but extend outside the boundaries of a standard temporal lobectomy (temporal plus) might well be misdiagnosed as reflecting a typical temporal lobe epilepsy (TLE), eventually leading to an incomplete surgical removal of the EZ and an increased risk of post-operative seizure relapse. Although this hypothesis have largely contributed to the pre-surgical method developed by several french epilepsy surgery centers, it has not yet been validated in a specific study.
METHODS: We have undertaken a retrospective and mutlicentric study of surgical results in populations presenting with a drug resistant TLE or temporal plus epilepsy who underwent surgery between 1990 and 1998 in our centers, and had more than two years post-operative follow-up. Temporal plus epilepsy was defined as an EZ including at least part of the anterior temporal lobe structures, as well as one of the three following brain regions : 1) the posterior temporal cortex behind the boundary of standard temporal lobectomy, eventually extending to the temporo-parieto-occipital junction, 2) the perisylvian area encompassing the insula, as well as the frontal and parietal operculum, or 3) the frontobasal or orbito-frontal cortex. Completeness of removal of the EZ was evaluated by comparing pre-surgical data with the post-operative MRI.
RESULTS: 281 patients were selected in this study, including 221 suffering from TLE, and 60 from a temporal plus epilepsy (21%). 182 patients has benefited from an intra-cranial EEG study, including all those with temporal plus epilepsy. A complete removal of the EZ was more frequently performed in TLE patients (97%), than in temporal plus epilepsy (65%) (p[lt]0.001). In both groups, patients whose EZ was fully removed had a significantly better seizure outcome than those with an incomplete removal (92% vs 17% of class I in TLE patients ; 74% vs 26% in temporal plus patients : p[lt]0.001). Considering all types of surgery, TLE patients had a significantly better seizure outcome than temporal plus epilepsy (90% vs 57% of class I : p[lt]0.001). Considering patients with either a normal MRI or signs of hippocampal sclerosis who underwent a standard anterior temporal lobectomy, the difference in outcome between TLE and temporal plus epilepsy was even more striking with 89% and 9% of class I, respectively.
CONCLUSIONS: Temporal plus epilepsy appears to represent a valid and clinically useful concept with respect to epilepsy surgery. Misdiagnosing patients with temporal plus epilepsy might account for a significant number of surgical failure in TLE, whereas recognizing those patients might enable to tailor a more extensive cortectomy resulting in a better seizure outcome.