Selected Papers: Neuroimaging

Abstract

Abstract *Taketoshi Maehara, *Tadashi Nariai, †Nobutaka Arai, ‡Kensuke Kawai, ‡Hiroyuki Shimizu, §Kenji Ishii, §Kiich Ishiwata, and *Kikuo Ohno *Neurosurgery, Department of Brain Medical Science, Tokyo Medical and Dental University; Bunkyo-ku ; †Department of Clinical Neuropathology, Tokyo Metropolitan Institute for Neuroscience, Fuchu ; ‡Department of Neurosurgery, Tokyo Metropolitan Neurological Hospital; Fuchu ; §Tokyo Metropolitan Institute of Gerontology; Itabashi, Tokyo, Japan . Purpose: We assessed the diagnostic value of 11C-methionine (MET)-PET in the differential diagnosis of benign tumors presenting with temporal lobe epilepsy. Methods: This series consisted of seven patients who had a type of complex partial seizure (CPS) associated with temporal lobe epilepsy, and were found to have benign tumors in the temporal lobe. They included three males and four females, ranging in age from 13 to 48 years. The age at seizure onset ranged from 6 to 26 years old, and the time to operation ranged from 2 to 28 years. High-resolution magnetic resonance imaging (MRI) with a 1.5 T magnet revealed organic lesions in the temporal lobes. MET-PET was performed in all seven patients, and 18F-fluoro-2-deoxy-glucose (FDG)-PET was performed in four patients. After presurgical examinations including repeated EEGs, video-EEG monitoring, and neuropsychological testing, three patients underwent invasive monitoring for focus detection and functional mapping. All seven patients underwent tumor resection together with focus excision under intraoperative ECoG guidance. Using the image analysis software Dr. View (Asahi Kasei Joho, Tokyo, Japan) on a personal computer, the region of interests (ROIs) were placed on the tumor and contralateral brain over the MRI, and then transferred to the PET images co-registered with MRI. The uptake of tracers was evaluated by the lesion-to-contralateral ratio (L/C ratio) and the standardized uptake value (SUV), a value calculated by dividing the brain activity of tracer per volume of brain by the injected activity of tracer per body weight. Surgical specimens were examined to investigate the tumor histology and Ki-67 labeling index. Microdygenesis of the resected foci was also examined. Statistical significance of differences in MET uptake between patients with dysembryoplastic neuroepithelial tumor (DNT) and those with ganglioglioma and gliomas was analyzed using the SUV and L/C ratio by the Student's t test. Results: After surgery, six patients remained seizure-free and one achieved a rare-seizure outcome for at least 6 months. The tumor was identified as high MET uptake lesion in three cases and was not depicted on MET-PET in four patients. Among the four patients who underwent FDG-PET, two patients showed high MET uptake in the tumor. However, all four patients showed low glucose uptake in the tumor and surrounding cerebral cortex. Pathological examination demonstrated DNTs in four cases, ganglioglioma in one case, low grade astrocytoma in one case, and pleomorphic xanthoastrocytoma (PXA) in one case. One patient with DNT showed a number of ectopic neurons in the white matter, a finding compatible with microdysgenesis. Ki-67 labeling index was 4% in one patient with DNT and 5% in one patient with PXA. The labeling index of the remaining five patients was 1% or lower. While four patients with DNT did not show visually high MET uptake, ganglioglioma and gliomas of the remaining three patients were identified as high-MET-uptake-lesions. MET uptake was significantly higher in patients with gliomas than in patients with DNT (SUV: P = 0.045, L/C ratio: P = 0.0079). The Ki-67 labeling index was not related to MET uptake expressed in SVU (P = 0.91) and L/C ratio (P = 0.38). Conclusion: In the seven patients with temporal lobe epilepsy and benign tumors in this study, we observed a high MET uptake in brain gliomas but not in DNTs. This high MET uptake was not related to the proliferation capacity measured by Ki-67 labeling index. MET-PET was useful for the differential diagnosis of DNT.