Long-term epilepsy surgery outcomes in patients with MRI-negative temporal lobe epilepsy

The outcome of surgery in patients with temporal lobe epilepsy (TLE) and normal high-resolution magnetic resonance imaging (MRI) has been significantly worse than in patients with unilateral hippocampal damage upon MRI. The purpose of this study was to determine the long-term outcomes of consecutive true MRI-negative TLE patients who all underwent standardized preoperative evaluation with intracranial electroencephalography (EEG) electrodes.

In this study we present all adult MRI-negative TLE surgery candidates evaluated between January 1990 and December 2006 at Kuopio Epilepsy Center in Kuopio University Hospital, which provides a national center for epilepsy surgery in Finland. During this period altogether 146 TLE surgery candidates were evaluated with intracranial electrodes, of whom 64 patients with normal high-resolution MRI were included in this study.

Among the 38 patients who finally underwent surgery, at the latest follow-up (mean 5.8 years), 15 (40%) were free of disabling seizures (Engel class I) and 6 (16%) were seizure-free (Engel class IA). Twenty-one (55%) of 38 patients had poor outcomes (Engel class III-IV). Outcomes did not change compared to 12-month follow-up. Histopathologic examination failed to reveal any focal pathology in 68% of our MR-negative cases. Only patients with noncongruent positron emission tomography (PET) results had worse outcomes (p = 0.044).

Our results suggest that epilepsy surgery outcomes in MRI-negative TLE patients are comparable with extratemporal epilepsy surgery in general. Seizure outcomes in the long-term also remain stable. Modern imaging techniques could further improve the postsurgical seizure-free rate. However, these patients usually require chronic intracranial EEG evaluation to define epileptogenic areas.