APPLICATION OF SPECTROSCOPIC IMAGING IN EPILEPSY

Functional and anatomical neuroimaging has had a dramatic effect on th e evaluation of patients for seizure surgery. The demonstration by PET that the epileptogenic focus has interictal metabolic abnormalities h as allowed a greater number of patients to come to seizure surgery, wi th fewer of these patients requiring intracranial electrode evaluation s. Metabolic changes have also been demonstrated utilizing single voxe l and whole brain H-1 and P-31 MRS imaging techniques with the interic tal focus characterized by increased Pi, pH, and decreased PME and NAA . These findings can be used to accurately lateralize temporal lobe as well as frontal lobe epilepsy. Furthermore, there is evidence that th ese findings can be used to localize the seizure focus with the change s specific for the epileptogenic region; although, more diffuse change s both ipsilaterally and contralaterally have been seen. In patients w ith anterior hippocampal seizure foci the pH is significantly alkaline only in the ipsilateral hippocampus, whereas the increased Pi and dec reased PME can be seen throughout the ipsilateral temporal lobe. When compared to controls the contralateral hemisphere is acidotic, Decreas ed NAA concentrations as well as NAA/Cr ratios have been demonstrated in the epileptogenic region in temporal and frontal lobe epilepsy. The decreased NAA has been correlated with the severity of cell loss, and may be a more sensitive measure than qualitative or quantitative meas ures of the hippocampal atrophy; however, the NAA decrease is more wid espread than just the epileptogenic focus but may be maximal at the si te of seizure initiation. In preliminary work, NAA maps of deviation f rom normality have suggested the maximal change to coincide with the e pileptogenic region. These results suggest that in focal epilepsy ther e is abnormal metabolic activity throughout the brain detectable by MR S, with patterns of metabolic asymmetry that are useful for seizure lo calization.