Surgical removal of mesial structures has been the leading treatment for refractory Mesial Temporal Lobe Epilepsy with hippocampus atrophy. However, few studies have performed a long-term evaluation of these patients.

This study aimed to evaluate postoperative structural changes on the contralateral hippocampus of patients with refractory Mesial Temporal Lobe Epilepsy, determining its correlation with surgical outcome. 

We performed a longitudinal study of 45 patients (38 controlled, 7 refractory) with unilateral hippocampal sclerosis, who underwent preoperative/postoperative (6 months after surgery) MRI acquired in a 3T scanner (Philips). We included 35 controls with 2 MRIs at long-term intervals. Manual hippocampal volumetry was performed (blinded for seizure outcome) with free software Display (Montreal Neurological Institute). After normalizing volumes with individual´s intracranial volumes, we used SPSS22 (repeated measures ANOVA) to test the interaction between time and groups. Statistical analyses were covariated for age and multiple comparisons adjusted with SIDAK. 

The paired comparison between preoperative and immediate postoperative (first week after surgery) hippocampal volume revealed non-significant volume reduction (p>0.05). However, at long-term evaluation, we observed significant atrophy of the contralateral hippocampus in both groups of patients (controlled, p<0.001, refractory=0.02), but no volumetric changes in controls (p=0.8). The mean interval of 2 MRIs was 2.6 years.

Manual volumetry can reveal a reduction in contralateral hippocampal volume that could not be detected by visual analysis. A speculative explanation could be an association with the deafferentation process triggered after severing the connections between both hippocampi via surgical intervention. These findings suggest that dynamic processes persist after surgery, and further studies may help to understand underlying mechanisms.