Abstract
The aim of the present study is to differentiate subtypes of hippocampal sclerosis (HS) using ex vivo ultra-high field magnetic resonance imaging (MRI). Included were 14 surgically resected hippocampi of patients with medically intractable temporal lobe epilepsy. The resected hippocampi were histologically categorized into subtypes of hippocampal sclerosis (HS type 1 (n = 10), HS type 2 (n = 2) and no-HS (n = 2)) and subsequently scanned on a preclinical 7T MRI acquiring T2-weighted morphology, relaxometry and diffusion tensor imaging. On the morphological images, the pyramidal cell layer (PCL) of the hippocampus was segmented and the following parameters were derived: T2 signal intensity, T1-, T2- and T2*-relaxation times, apparent diffusion coefficient (ADC), fractional anisotropy (FA) and mean diffusivity (MD). Furthermore, the area of the PCL was determined, as well as the parameter product which refers to the widths of the PCL parallel and perpendicular to the stratum moleculare. Spearman correlation coefficient was used to demonstrate relationships between MR-parameters and type of sclerosis. In comparison to no-HS specimens, the PCL was significantly narrower in HS type 1 and HS type 2 hippocampi. This narrowing affected the entire cornu ammonis sector (CA) 1 in HS type 1, while it was limited to the upper half of CA1 in direction to CA2 in HS type 2. The parameter product median increased from 0.43 to 1.67 and 2.91 mm2 for HS type 1, HS type 2 and no-HS, respectively. Correlation coefficients were significant for the PCL parameters product (0.73), area (0.71), T2*-time (-0.67), FA (0.65) and ADC (0.55). Our initial results suggest that HS type 1, HS type 2 and no-HS subtypes can be distinguished from each other using ex vivo UHF MRI based on T2-weighted morphologic images and the assessment of the parameter product. Upon clinical translation, UHF-MRI may provide a promising technique for the preoperative differentiation of HS subtypes in patients.
Highlights
Hippocampal sclerosis (HS) is observed in up to 70% of patients with mesial temporal lobe epilepsy (TLE) [1]
The question we focus on in this ex vivo study is whether HS characteristics can be visualized and quantified by morphological and multiparametric UHF Magnetic resonance imaging (MRI)
The study results can be divided into a qualitative analysis, based on morphologic T2-weighted MR images, and a quantitative part, including the parameters area, product, T2 signal intensity (a.u.), T1-time, T2-time, T2Ã-time, fractional anisotropy (FA) (a.u.), apparent diffusion coefficient (ADC) (Ã10−6 mm2/s) and mean diffusivity (MD) (Ã10−6 mm2/s)
Summary
Hippocampal sclerosis (HS) is observed in up to 70% of patients with mesial temporal lobe epilepsy (TLE) [1]. Up to one third of TLE patients suffer from intractable or drug-resistant epilepsy, and based on the evidence of hippocampal involvement in seizure generation, surgical resection of the ipsilateral hippocampus is the standard of care for these patients [2,3,4]. According to the International League against Epilepsia (ILAE), HS can be histologically divided into four subtypes based on specific patterns of neuronal cell loss in the pyramidal cell layer (PCL) [5]. Typical features of HS are reduced hippocampal volume, increased signal intensity of the PCL on T2-weighted and T2-fluid attenuation inversion recovery (FLAIR) images and loss of internal architecture [13,14]. An increase of the mean diffusivity (MD) and a reduction of fractional anisotropy (FA) have been reported in patients with HS [15,16,17]
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