Seeking subtle lesions for 'MRI-negative' frontal lobe epilepsy

Frontal lobe epilepsy that is not detected on magnetic resonance imaging (MRI) is one of the difficult epilepsy syndromes in epilepsy surgery due to poor seizure outcomes. However, subtle lesions, such as focal cortical dysplasia, would have been overlooked and diagnosed as MRI 'negative' epilepsy in some MRI-negative cases. This study conducted a detailed MRI assessment for patients who had previously been diagnosed with MRI-negative frontal lobe epilepsy. We tried to find subtle lesions using 3T MRI, single photon emission computed tomography (SPECT), and 18F fluorodeoxyglucose positron emission tomography (FDG-PET). We detected subtle lesions in 15 out of 32 cases. The surgical treatment for the 15 cases resulted in good seizure outcomes (Engel class I: 73%), while the rest of the 17 cases demonstrated poor outcomes (Engel class I: 37%)[P < 0.05]. Additionally, most of the subtle lesion-positive cases skipped chronic subdural grid implantation. Therefore, detecting subtle lesions should be an important approach for patients previously suspected of MRI-negative frontal lobe epilepsy. However, this study revealed that we were still unable to detect subtle lesions in 17 of the 32 cases. Device innovation and imaging diagnosis development would help detect more subtle lesions and cause better surgical outcomes in the future. (author)