Histopathological substrate of increased T2 signal in the anterior temporal lobe white matter in temporal lobe epilepsy associated with hippocampal sclerosis

Objective: This study was undertaken to analyze the histology underlying increased T2 signal intensity (iT2SI) in anterior temporal lobe white matter (aTLWM) epilepsy due to hippocampal sclerosis (TLE/HS). Methods: Twenty-three patients were included: 16 with increased T2 signal in the aTLWM and seven with HS only. Magnetic resonance imaging (MRI) findings were consistent across two neuroradiologists (kappa = .89, p < .001). Quantification of neuronal cells, astrocytes, oligodendrocytes, and vacuolization in the white matter of temporal lobe specimens was performed by immunohistochemistry (neuronal nuclear antigen, glial fibrillary acidic protein, oligodendrocyte transcription factor, and basic myelin protein, respectively). Surgical specimens from TLE/HS patients with and without iT2SI in the aTLWM were compared. Samples of aTLWM were divided into three groups, according to MRI features: G1 = samples of iT2SI, G2 = samples with normal T2 signal intensity from patients without white matter imaging abnormalities, and G3 = samples with normal T2 signal intensity adjacent to areas with iT2SI. Results: Patients with increased T2 signal had a significantly younger age at epilepsy onset (p < .035). Histological analysis revealed a higher percentage of vacuolar area in these patients (p < .004) along with a lower number of ectopic neurons (p = .042). No significant differences were found in astrocyte or oligodendrocyte counts among groups. Significance: A higher proportion of vacuoles in regions with iT2SI may be the histopathologic substrate of this signal alteration in the white matter of the temporal lobe in patients with TLE/HS. This method of quantifying vacuoles using digital image analysis proved reliable and cost-effective.