Abstracts

Rationale: The presence of unilateral hippocampal atrophy (HA) in the evaluation of MTLE is often a defining factor that if concordant with the EEG and PET, and is not contraindicated from neuropsychological data, will typically result in candidacy for surgical resection. However, it is possible to have HA without intractable seizures, as seen in familial MTLE (Kobayashi et al 2003). We used ultra-high field MR spectroscopic imaging at 7T to assess MTLE with patients who are all HA positive. We studied n=11 patients who were medically intractable and n=2 patients who were very well controlled (seizure free for >2years on medication). Methods: Clinical: All patients (n=13) were recruited from the Yale Epilepsy Program. All patients demonstrated hippocampal atrophy on conventional MR imaging (n=9 R HA; n=4 L HA). All except 1 of the 13 patients also had Phase 1 monitoring data that demonstrated clinical and lateralized electrographic changes that were consistent with the side of hippocampal atrophy. One surgical patient who had been seizure free >2 years sought surgical resection for the purposes of medication discontinuation. One non-surgical patient was medically well controlled on monotherapy, and had semiology consistent with medial temporal lobe epilepsy. Imaging: We used a head only Varian 7T MR system with an 8 element transceiver array for all studies. All acquisitions targeted the medial temporal lobes and were angulated along the planum temporale. A moderate TE40msec spin echo sequence was used to acquire measurements of the singlet resonances including NAA, creatine and choline. This acquisition was used to minimize contributions from overlapping amino acids (glutamate, glutamine). The nominal voxel size is 0.64cc. A single voxel reconstruction technique was used to consistently place the hippocampal spectra in three loci as shown in Fig 1. Results: Spectral data from a patient are shown in Fig. 1. As a group, the n=11 patients who were medically intractable demonstrated a significantly higher (abnormal) Cr/NAA value in the ipsilateral medial temporal lobe anteriorly in comparison to control (1.06 0.21 patients vs. 0.83 0.04 controls; p<0.005, Table). The n=2 patients who were well controlled had values of 0.84 and 0.65, mean 0.74. Conclusions: Spectroscopic imaging at 7T of medically intractable MTLE is consistent with previous data showing a mean ~28% drop in NAA/Cr in comparison to control. The two patients with MRI documented hippocampal atrophy but who were medically seizure free had NAA/Cr values similar to control. As an evaluation of neuronal mitochondrial function, these data are consistent with the view that NAA/Cr reflects ongoing dysfunction and may be more accurate for an assessment of tissue health than tissue loss directly.