Neuroimaging and presurgical evaluation of symptomatic epilepsies.

The goal of presurgical evaluation of intractable epilepsy is to identify epileptogenic regions in the brain. From our experience of 38 cases of resective epilepsy surgery from the last 3 years, ictal SPECT was considered the most sensitive at detecting focal changes relating to seizures compared to other neuroimaging modalities, such as MRI, FDG-PET, SPECT and MEG. At interictal state, on the other hand, FDG-PET was most sensitive, especially in cases with focal cortical dysplasia, which is often MRI-invisible. In dysplastic tumors, MRI showed the highest concordance rate to clinically verified epileptogenic regions. Activation studies using functional neuroimaging such as PET and fMRI is useful to evaluate brain functions at epileptogenic regions presurgically. The role of functional brain imaging in epilepsy surgery is considered to be: (i). case selection for resective surgery, (ii). case selection for invasive EEG monitoring, and (iii). navigation of electrode placement and cortical resection.