Qualitative MR imaging of refractory temporal lobe epilepsy requiring surgery: Correlation with pathology and seizure outcome after surgery

OBJECTIVE. The purpose of this study was to compare MR imaging findings with histologic findings of either hippocampal sclerosis or gliosis in patients with intractable temporal lobe epilepsy requiring surgery and to correlate MR imaging findings with seizure outcome after surgery and with clinical parameters such as febrile seizure history. MATERIALS AND METHODS. A retrospective study of MR scans of 66 patients with medically refractory temporal lobe epilepsy requiring surgery was performed. Qualitative diagnosis was done by visual inspection of MR images. MR imaging findings of hippocampal atrophy, signal intensity changes, and segmental findings were correlated with histopathology and with neuronal density. The final MR imaging diagnosis was also correlated with seizure outcome after surgery and with febrile seizure history. RESULTS. Histologic findings consisted of hippocampal sclerosis in 55 patients and nonspecific gliosis in 11 patients. Two variables, MR imaging findings of hippocampal sclerosis (hippocampal atrophy or signal intensity change) and a febrile seizure history, were significantly associated with hippocampal sclerosis. MR images of nonspecific gliosis usually showed normal findings, although some cases showed mild hippocampal atrophy. When comparing MR imaging findings with histology, our observers achieved sensitivities of 87-98% and specificities of 45-100%. In patients with successful outcomes after surgery, sensitivity ranged from 85% to 98% for MR imaging findings suggesting hippocampal sclerosis, specificity ranged from 17% to 85%, and positive predictive values ranged from 82% to 90%. CONCLUSION. Qualitative visual analysis of MR images correlates well with histologic findings, febrile seizure history, and seizure outcome after surgery. MR imaging findings and febrile seizure history help differentiate between hippocampal sclerosis and nonspecific gliosis, two similar clinical conditions associated with temporal lobe epilepsy that often have different outcomes after surgery.