Three-dimensional preoperative maps of hippocampal atrophy predict surgical outcomes in temporal lobe epilepsy

Abstract

The authors used surface-based anatomic mapping to detect features of hippocampal anatomy that correlated with surgical outcomes in patients undergoing surgery for mesial temporal lobe epilepsy with hippocampal sclerosis. Compared with a seizure-free group, hippocampal profiles for the non-seizure-free group had greater diffuse ipsilateral atrophy and more region-specific contralateral atrophy in the anterior, lateral hippocampus. These atrophic regions may indicate areas of increased epileptogenicity, contributing to poorer surgical outcomes.

Figure 1

Steps involved in three-dimensional hippocampal modeling. Each individual’s hippocampus is traced in consecutive coronal MRI sections (A) and converted to a three-dimensional parametric surface (B) in which the radial size of the hippocampus is measured from a centerline and plotted in color on the surface, to index radial atrophy. These meshes are averaged across subjects (C) and atrophy relative to the contralateral hippocampus in each surgical outcome group (seizure free and not seizure free) and across the two surgical outcome groups is computed at each surface grid point (D)

Figure 2

Maps identifying regions where seizure-free (SF) and non– seizure-free (NSF) surgical outcome groups differ in their degree of atrophy (A and B) and regions of hippocampal asymmetry in each surgical outcome group (C and D). Group difference maps show mean hippocampal volume differences ipsilateral (A) and contralateral (B) to the side of seizure onset. Areas of significant atrophy between the two surgical outcome groups are plotted as a map of p values. The NSF groups show significantly greater diffuse atrophy in the ipsilateral hippocampus (A), whereas the contralateral side shows more region-specific atrophy pattern (B). Maximal atrophy is seen in the anterior and lateral aspects of the contralateral hippocampus. The average distribution of atrophy was computed for patients with seizure-free postsurgical outcome (C) and those who continued to have seizures (D) by directly comparing the ipsilateral to the contralateral hippocampus. Areas of significant asymmetry are visualized as a map of p values. Both SF and NSF groups showed severe diffuse deficits along the entire hippocampus. The overall asymmetry pattern suggests that the NSF group (D) had a lesser degree of asymmetry when compared with the SF group (C). However, the anterior to posterior distribution of the asymmetry pattern does not differentiate the two surgical groups.