Mammillary body changes and seizure outcome after laser interstitial thermal therapy of the mesial temporal lobe

Objective: The mammillary bodies have long been known as the primary relay center for the hippocampus. The fornix is the primary efferent pathway of the hippocampus, with its postcommissural fibers terminating in the mammillary bodies. In this study, we describe change in mammillary body volume after laser interstitial thermal therapy (LiTT) for mesial temporal lobe epilepsy and correlate it with seizure outcome. Methods: Pre-and post-LiTT ablation magnetic resonance imaging was reviewed in axial and coronal planes to determine mammillary body volume as calculated by the ellipsoid method. Patient demographics, clinical semiology, and seizure localization were analyzed. The primary end -point was seizure freedom at 1 year after LiTT. The change in the size of the mammillary body were correlated with the postoperative seizure freedom at 1 year using the Wilcoxon/Kruskal-Wallis test for statistical significance. Results: Between December 1, 2012 and June 1, 2015, 22 patients underwent LiTT for mesial temporal lobe epilepsy. Two patients were excluded due to lack of follow-up. Of the remaining 20 patients, 13 were seizure free at 1 year. In the seizure free group, there was an average 34.6% (13%) decline in ipsilateral mammillary body volume, as opposed to an average decline of 8.4% (10.9%) in patients with continued seizures (P = 0.0026). Conclusions: Our findings show a statistically significant correlation between postoperative volume reduction in ipsilateral mammillary body and seizure outcomes after LiTT. With further validation, this finding could be a useful marker of adequacy of ablation independent of ablation volumes and determinant of potential benefit of additional surgical intervention in patients with poor outcomes after LiTT.