Magnetic resonance imaging findings in temporal lobe epilepsy

Purpose: To describe the findings of magnetic resonance imaging (MRI) in patients with temporal lobe epilepsy (TLE). Materials and Methods: A retrospective review of MRI studies was performed in 105 (61 male and 44 female) patients with clinical and electroencephalographic (EEG) evidence of TLE (mean age 28 years). Of the 105 patients, 46 underwent temporal lobectomy including resection of the hippocampus. All MRI studies were performed using a 1.0 T or 1.5 T unit with sagittal T-1 and axial T-2-weighted fast spin echo images. Oblique coronal images were obtained perpendicular to the long axis of the hippocampus with three-dimensional MPRAGE T-1- and fast spin echo T-2-weighted images. MRI diagnosis of hippocampal sclerosis was based on the presence of either unilateral hippocampal atrophy or high signal intensity of the hippocampus on T-2-weighted images. The MRI findings of hippocampal sclerosis were analyzed only in those patients with either surgical proof of hippocampal sclerosis or an MRI diagnosis of hippocampal sclerosis that was concordant with the video/EEG lateralization. Results: The MRI diagnosis in the 105 patients consisted of hippocampal sclerosis (70/105, 66%), hemiatrophy (4/105, 4%), localized tissue loss (4/105, 4%), tumor (3/105, 3%), and diffuse atrophy (2/105, 2%). No abnormality was detected in 22 cases (21%). Of the 70 patients with MRI findings indicative of hippocampal sclerosis, 63 with either surgical proof or concordant EEG received a final diagnosis of hippocampal sclerosis. Among those 63 patients, MRI showed hippocampal atrophy (58/63, 92%), high signal intensity of the hippocampus on T-2-weighted images (40/63, 63%), enlargement of the ipsilateral temporal horn (39/63, 62%), atrophy of ipsilateral fornix or mamillary body (16/63, 25%), and ipsilateral temporal lobe atrophy (4/63, 6%). Conclusion: In TLE, the most common abnormality seen on MRT was hippocampal sclerosis (approximately 66%). The MRT appeared normal in 21% of patients with TLE. Proper clinical management of these patients requires complementary studies including ictal SPECT, PET, or invasive EEG, particularly in those patients in whom results of MRI are normal or not concordant with EEG.