Single Voxel Proton MR Spectroscopy in Hippocampal Sclerosis

Abstract

To evaluate proton MR spectroscopy (MRS) of patients with hippocampal sclerosis (HS). We obtained MRS spectra from both hippocampi of 20 normal adult volunteers and 25 patients with unilateral HS as seen on MR images. The MRS was performed on a 1.5 T MR unit by using PRESS sequence with 1500 TR and 136 TE. We used multiple voxel sizes ranging from 6 cm³ (2.0 cm × 2.0 cm × 1.5 cm) to 1 cm³ (1.0 cm × 1.0 cm × 1.0 cm) to see the effect of voxel size change. NAA/Cho and NAA/Cr ratios were calculated and the results were compared between normal control subjects and the patients with HS.

In HS patients, mean NAA/Cho and NAA/Cr ratios of the ipsilateral hippocampus were significantly lower than those of contralateral hippocampus (NAA/Cho: 0.78 ± 0.19 vs. 0.91 ± 0.19; NAA /Cr: 0.95 ± 0.23 vs. 1.11 ± 0.25). Mean NAA/Cho and NAA/Cr ratios of the contralateral hippocampus of HS patients were also significantly lower than those of normal control subjects (NAA/Cho: 0.91 ± 0.19 vs. 1.19 ± 0.35, NAA/Cr: 1.11 ± 0.25 vs. 1.53 ± 0.64). However, there was wide overlapping in both NAA/Cho and NAA/Cr ratios between the ipsilateral and contralateral hippocampus of HS patients and normal subjects. With the threshold value of either NAA/Cho being 0.8 or NAA/Cr being 1.0 (95% confidence level), sensitivity of MRS was 72% (18/25), when MRI was used as a gold standard. When combination of MRI, PET, invasive study and/or surgery was used as a gold standard, it was 57% (13/23). Bilateral abnormality was noted in 24% (6/25). There were trends for better sensitivity with smaller voxel size and with NAA/Cho rather than NAA/Cr.

Single voxel proton MRS may be a useful, promising diagnostic tool in the evaluation of hippocampal sclerosis. However, one should be cautious in interpreting the data, because there is a wide overlap in both NAA/Cho and NAA/Cr ratios between the hippocampi of normal subjects and HS patients.