Limbic system abnormalities associated with Ammon's horn sclerosis do not alter seizure outcome after amygdalohippocampectomy

Purpose: To evaluate whether limbic system abnormalities associated with Ammon's horn sclerosis alter seizure outcome after selective amgydalohippocampectomy. Methods: In 45 patients with unilateral mesial temporal lobe epilepsy, histologically proven Ammon's horn sclerosis, and uneventful postoperative course, volumes of the hippocampus, hemisphere, amygdala, entorhinal cortex, mamillary body, and fornix were measured by using a T-1-weighted 3-D gradient-echo sequence with roughly isotropic (1.17 x 1.17 x 1-mm) voxels. In addition, signal intensity of the hippocampus and of the temporal lobe white matter was visually assessed and graded on a coronal T-2-weighted fast-spin-echo sequence with 2-mm-thick slices. Volumetric measurements and visual analysis were compared between seizure-free and non-seizure-free patients examined 12 months after surgery. Results: Hippocampal, hemispheric, entorhinal cortex, mamillary body, and fornix volumes, but not amygdalar volumes, were significantly smaller on the operated-on than on the non-operated-on side and significantly smaller in patients compared with controls. No volume differences of the hippocampus, hemisphere, amygdala, entorhinal cortex, mamillary body, and fornix existed between seizure-free (Engel class IA) and non-seizure-free patients (Engel class IB-IV). Increased temporal lobe white matter signal was observed in 15 patients but did not alter seizure outcome. Conclusions: Limbic system abnormalities are not a surrogate marker to predict postsurgical seizure outcome in patients with unilateral Ammon's horn sclerosis.