Identifying Morphological Patterns of Hippocampal Atrophy in Patients With Mesial Temporal Lobe Epilepsy and Alzheimer Disease

Abstract

Purpose: Mesial temporal lobe epilepsy (MTLE) and Alzheimer's disease (AD) are two distinct neurological disorders associated with hippocampal atrophy. Our goal is to analyze the morphologic patterns of hippocampal atrophy to better understand the underlying pathological and clinical characteristics of the two conditions. Methods: Twenty-five patients with AD and 20 healthy controls with matched age and gender were recruited into the AD group. Twenty-three MTLE patients and 28 healthy controls with matched age and gender were recruited into the MTLE group. All subjects were scanned on 3T-MRI scanner. Automated volumetric analysis was applied to measure and compare the hippocampal volume of the two respective groups. Vertex-based morphologic analysis was applied to characterize the morphologic patterns of hippocampal atrophy within and between groups, and a correlation analysis was performed. Results: Volumetric analysis revealed significantly decreased hippocampal volume in both AD and MTLE patients compared to the controls. In the patients with AD, the mean total hippocampal volume was 32.70% smaller than that of healthy controls, without a significant difference between the left and the right hippocampus (p < 0.05). In patients with MTLE, a significant reduction in unilateral hippocampal volume was observed, with a mean volume reduction of 28.38% as compared with healthy controls (p < 0.05). Vertex-based morphologic analysis revealed a generalized shrinkage of the hippocampi in AD patients, especially in bilateral medial and lateral regions. In MTLE group, atrophy was seen in the ipsilateral head, ipsilateral lateral body and slightly contralateral tail of the hippocampus (FWE-corrected, p < 0.05). Conclusions: MTLE and AD have distinctive morphologic patterns of hippocampal atrophy, which provide new insight into the radiology-pathology correlation in these diseases.

Keywords: Alzheimer's disease; hippocampus; mesial temporal lobe epilepsy; morphologic analysis; volumetric analysis.

Figure 1

Hippocampus and subcortical structure delineation by different image segmentation tools. (A) Segmentation of hippocampus using the FreeSurfer surface delineation (blue) and manual delineation of the hippocampus (red) on coronal slices. (B) Automated segmentation of subcortical structures (including hippocampus, amygdala, caudate, nucleus accumbens, putamen, globus pallidus, and thalamus) by FSL-FIRST.

Figure 2

Comparisons of hippocampal volume between patients and controls. (A) The average volume of the ipsilateral hippocampus of the patients with MTLE was 28.38% (1,050 mm³) less than that of the healthy controls (p < 0.05). (B) The average volume of the hippocampi in patients with AD was 32.70% (817.44 mm³) less than that of the healthy controls (p < 0.05). MTLE, mesial temporal lobe epilepsy; AD, Alzheimer's disease.

Figure 3

Morphologic views of hippocampi in patients with MTLE (B,D,F,H) and AD (A,C,E,G) from a superior, inferior, right lateral side and left lateral side. The results were color-coded by uncorrected F-statistic values. The transition from red to blue indicates an increase from lower to higher statistical significance, with blue indicating p < 0.05. Patients with MTLE had hippocampal atrophy predominantly in the ipsilateral head, partly in the ipsilateral lateral body and slightly in the contralateral tail (blue). The right-sided atrophic hippocampi of patients with MTLE were flipped to the left to facilitate comparison with those of the patients with AD. Patients with AD had generalized bilateral hippocampal atrophy, primarily in the medial and lateral regions and a small proportion of anterior and posterior regions (blue), most of the anterior and posterior regions had no significant atrophy (green and red). MTLE, mesial temporal lobe epilepsy; AD, Alzheimer's disease; FWE, Family-Wise Error.