Limited Predictive Ability of Hippocampal Single Voxel MR Spectroscopy in Surgically Proven Epilepsy

ABSTRACT

OBJECTIVE: The authors evaluate the predictability of single voxel proton magnetic resonance spectroscopy(MRS) for hippocampal abnormalities in medial temporal lobe epilepsy(MTLE), lateral temporal lobe epilepsy(latTLE) and extratemporal lobe epilepsy(extraTLE). METHODS: Twenty healthy volunteers and 42 patients with MTLE, 17 with latTLE and 23 with extraTLE, were examined preoperatively with MRS. The NAA/(Cho+Cr) ratios were calculated from the MRS peaks obtained bilaterally from both hippocampi. RESULTS: The mean NAA/(Cr+Cho) ratios showed a stepwise increase from the ipsilateral hippocampus in the MTLE group to the normal control group. In the 42 MTLE patients, the mean NAA/(Cho+Cr) ratio value for the ipsilateral hippocampus was 0.39. This was 17.3% lower than the 0.489 measured for the contralateral hippocampus (p=0.005). This was also significantly lower when compared with the hippocampi of latTLE and extraTLE patients ipsilateral to the epileptogenic zone and also with the normal control group (p< 0.05). The mean ratio value of the contralateral hippocampi was also significantly lower when compared with the normal control group (p=0.000). The mean ratio value measured on postoperative MRS showed little metabolic recovery in the MTLE (from 0.455 to 0.481, p=0.48) compared to the latTLE (from 0.438 to 0.52, p=0.09). CONCLUSION: The MRS might be inconclusive in determining whether the non-epileptogenic hippocampus is affected by epileptiform discharge propagation from the epileptogenic hippocampus or from the remote epileptogenic zone other than the hippocampus. Therefore, physicians should be cautious when determining whether the contralateral hippocampus in MTLE or both hippocampi in neocortical epilepsy is abnormal and whether they should be resected together with the epileptogenic zone.