Abstracts

Rationale: Management of patients with mesial temporal lobe epilepsy (MTLE) with evidence of hippocampal sclerosis (HS) on brain MRI is now considered relatively straightforward with most centers reporting favorable outcomes in upto 80% cases, after anterior temporal resection. Risk of post-operative memory dysfunction is thought to be reduced by the presence of HS on brain MRI. Little, however, is known about outcome in patients with MTLE and normal brain MRI. We present clinical, EEG and neuropsychologic data in a series of patients with MTLE and normal brain MRI who had resective surgery. Methods: 16 of 254 patients with refractory temporal lobe epilepsy who had resective surgery at Henry Ford Hospital (1995 to 2007) met inclusion criteria: 1) Normal high resolution brain MRI; 2) Mesial temporal epileptogenic zone as determined by intracranial EEG; 3) Post-surgical follow-up of at least 1 year. Results: 16 (12 females) patients had surgery at a median age of 33 years (21-52 years). Seizure frequency ranged from an average of one seizure every 2 months to multiple daily seizures. Patients had failed a mean of 5.6 ± 1.75 antiepileptic drugs (AED's) prior to surgery. Scalp EEG revealed bitemporal inter-ictal discharges in 5 patients; 10 patients had inter-ictal discharges localized to one temporal lobe. Scalp EEG seizure onset was unitemporal in 10 patients, regional/hemispheric (2), bitemporal (1), and non-localizable in 1 patient. No scalp EEG data was available on 1 patient. SPECT scan (interictal/ictal)was helpful in localization/lateralization in 7 of 16 patients. 13 patients had video EEG monitoring after implantation of intracranial electrodes which revealed seizure onset from mesio-basal temporal regions. All 16 patients had electrocorticography with predominant spiking noted in the mesiobasal temporal regions. 13 of 16 patients had left sided resection. 13 patients had amygdalo-hippocampectomy (1 selective; 12 had additional antero-inferior temporal resection). The hippocampus was left intact in the 3 remaining patients who had anterior temporal lobectomy with uncal resection. After a median follow up of 8 years (1 to 12 years), 10 patients (62%) had Engel Class 1 outcome, 4 (25%) had Class 2, and 2 patients (13%) had a Class 3 outcome. Patients were on a mean of 1.8 ± 0.91 AED's at last follow-up with one patient completely off medications. In the 9 patients, who had 1 year post-operative neuropsychologic data available, 4 reported improvement in verbal memory function after left temporal resection, 1 reported imrovement in non-verbal memory after right temporal resection, 1 reported no change and 3 patients reported worsening verbal memory after left temporal resection. Pathologic exam revealed HS (5), dysplasia (2), dual pathology (2), non-specific changes (7) and was not available in 1 case. Conclusions: Our data suggests that resective surgery is an effective treatment option in patients with refractory MTLE and normal brain MRI scans, with 87% patients reporting good post-operative outcome with regard to seizure freedom.