Abstracts

Rationale: Magnetic resonance (MR) volumetry studies have showed progressive contralateral hippocampal atrophy after surgery for medically intractable temporal lobe epilepsy. Significantly less atrophy of the contralateral hippocampus was observed in seizure free patients. We evaluate long-term post-operative hippocampal volume (HV) on non-epileptic hippocampus using MR volumetry in patients who underwent surgery for unilateral mesial temporal lobe epilepsy (MTLE) and achieved seizure freedom. Methods: We studied 1.5-Tesla MRI before and after epilepsy surgery in 24 patients (age13 to 53 years, mean: 36.9 years) with MTLE. Serial MRI studies were scheduled at 4 post-operative periods between1 period; 6 months and 1year (6m-1y),2; 1 and 2 years (1-2 y), 3; 2 and 3 years (2—3 y), and 4; 3 and 5 years (3-5 y). The non-epileptic HV were measured from MRI scans according to the Wu’s method (AJNR, 2005). We compared the HV of patients with those of age-matched controls (n=14). We analyzed the correlation between consecutive post-operative non-epileptic HV and seizure duration, age at surgery, pre-operative both epileptogenic HV and non-epileptic HV. Results: Twenty-four patients with MTLE were analyzed, after anterior temporal lobectomy in 19 patients and selective amygdalohippocampectomy in 5 patients. All patients were seizure-free after surgery. The seizure duration ranged from 7 to 52 years (mean: 26.5 years). The epileptogenic HV before surgery was 0.81±0.28 cm3 (mean±SD), significantly smaller than the non-epileptic HV (1.32±0.37 cm3) (p < 0.01). The pre-operative non-epileptic HV was also significantly smaller than HV of controls (right: 1.58±0.25; left: 1.54±0.21). During the follow-up period, the volume reduction (%) of post-operative HVs compared to pre-operative HVs were 1;-6.0±8.7, 2;-1.5±9.0, 3;-4.9±9.7, and 4;-5.7±8.7% at the post-operative consecutive periods. There was a significantly progressive atrophy of the HV over the follow-up periods (p < 0.01). The progression of atrophy was correlated with the age at surgery (p < 0.01) and pre-operative non-epileptic HV (p < 0.01), but not correlated with seizure duration. Conclusions: In patients who achieved seizure freedom after the resection of hippocampal sclerosis, the progression of non-epileptic hippocampal atrophy was significantly more pronounced in patients with older age at surgery and larger pre-operative non-epileptic hippocampus. The achievement of seizure freedom in patients with MTLE could not guarantee the non-epileptic hippocampus changes. The volume of functional hippocampus can be affected by the resection of epileptogenic hippocampus which might support the memory function for the contralateral hippocampus. Thus, after the epileptogenic hippocampus is resected, the remaining hippocampus alone might exhaust, especially in elders. Funding: None