Abstracts

Rationale: Magnetic resonance (MR) volumetry studies have showed longitudinal deceases of the hippocampal volume (HV) in patients with newly diagnosed focal epilepsy. We examined the long-term HV changes after contralateral hippocampectomy in patients with mesial temporal lobe epilepsy (MTLE) to elucidate whether non-epileptic hippocampal damage could be progressive or not after surgery.Methods: Ten patients with typical MTLE were scanned with 1.5-Tesla MRI before anterior temporal lobectomy. A typical MTLE was defined as epilepsy with complex partial seizures, unilateral hippocampal atrophy with hyperintensity on FLIAR and/or T2-weighted images on MRI, and concordant localization results from ictal/interictal scalp-video EEG monitoring. Serial MRI studies were scheduled at postoperative 1 and >2 years in the follow-up study. The non-epileptic HVs were measured from MRI scans according to the Wu s method (AJNR, 2005). We compared the HVs of patients with those of age-matched controls (n=14), and the results were subjected to neuropsychological examination.Results: No difference in age was observed between controls (35 11.3 years; mean SD) and patients (36.7 8.2 years) at surgery. The seizure duration ranged from 15 to 37 years (mean: 27.5 years). The epileptogenic HV before surgery was 0.97 0.34 cm3 (mean SD), significantly (p<0.01) smaller than the non-epileptic HV (1.61 0.40 cm3). The preoperative non-epileptic HV was not significantly different from HVs of controls (right: 1.58 0.25; left: 1.54 0.21). During the follow-up period (15-40 months), HVs of patients decreased at postoperative 1 (1.55 0.37) and >2 (1.41 0.33) years. There was a significant difference (p<0.05) between preoperative and postoperative (>2 years) HVs. The mean HV decrease rate was 9.9 % (range: 0-19%) at postoperative > 2 years. All patients experienced no seizure after surgery. Neuropsychological examinations revealed a decline of memory function and/or intelligence in 3 of 4 patients with left MTLE in the follow-up period. Neuropsychological functions in 6 patients with right MTLE remained unchanged, and in fact improvements were observed in one patient.Conclusions: Decreases in the non-epileptic HVs occurred in patients with anterior temporal lobectomy during postoperative 1 and > 2 years, although seizures were terminated. The findings suggest that achieving a good seizure control with surgery may not completely halt further progressive hippocampal damage, although excessive seizures have once affected the non-epileptic hippocampus for an extended period before surgery. However, the extent of the volume decreases was not enough to affect the neuropsychological findings in this study.