Histopathology of 3 Tesla MRI-negative temporal lobe epilepsies

Abstract

Introduction: Histopathology of MRI-negative temporal lobe epilepsies (TLE) shows heterogeneous findings. The use of either 1.5 or 3 Tesla MRI for the selection of MRI-negative cases and use of older classification systems instead of the current ILAE classification system may account for this heterogeneity. We focus on histopathology of 3 Tesla MRI-negative TLE according to ILAE criteria and investigate potential correlation to seizure outcome 1 year postoperatively.

Materials and methods: Twenty specimens (9 neocortical, 11 hippocampal) from eleven 3 Tesla MRI-negative patients with TLE were examined in two steps. Standard stains and immunohistochemical reactions as well as Palmini and Wyler criteria were used prospectively during the initial examination. Retrospectively, all specimens were re-examined and re-evaluated. Phospho-6 and calretinin stains and the ILAE criteria were used during the review examination.

Results: Initial examination revealed 7 focal cortical dysplasias (FCDs) Palmini type 1, two cases of cortical gliosis, 4 cases of hippocampal sclerosis (HS) Wyler grade 1 and seven cases of hippocampal gliosis. The review examination according to ILAE criteria revealed 4 FCDs type I and 5 mild malformations of cortical development. All hippocampal specimens showed "no HS/gliosis only" after the review examination. Histopathology showed no correlation to seizure outcome.

Discussion: This is the first histopathological study to include only 3 Tesla MRI-negative cases. The use of ILAE criteria lead to the diagnosis of "no HS/gliosis only" of all hippocampal specimens, a finding not in line with previously reported series. The spectrum of diagnoses within neocortical specimens showed accordingly more mild findings.

Keywords: Histopathology; MRI-negative; Surgery seizure outcome; Temporal lobe epilepsy.