Abstracts

Rationale: The first 7-Tesla (7T) MRI scanner was FDA approved for clinical diagnostic use in October 2017; studies on the usefulness of this new technology in clinical practice are highly necessary. Here we aim to assess the clinical value of in vivo structural 7T MRI and its post-processing for the noninvasive identification of epileptic brain lesions in a large cohort of patients with pharmacoresistant epilepsy undergoing presurgical evaluation. Methods: One hundred patients were included (53 with non-lesional and 47 with lesional 3T MRI). An epilepsy protocol was used for the 7T acquisition. Post-processing of the 7T T1-weighted MP2RAGE sequence was performed using the morphometric analysis program (MAP) with comparison to a normal database consisting of 50 healthy controls. Review of 7T was performed by an experienced board-certified neuroradiologist. The clinical significance of 7T findings was assessed based on intracranial EEG (ICEEG) ictal onset, surgery, post-operative seizure outcomes and histopathology. Results: In the 3T-nonlesional group, 7T detected previously unappreciated subtle lesions in 26 patients (49%, 12 detected by unaided review, examples shown in Figure 1; 22 by MAP-guided review, examples shown in Figure 2). The location of the 7T-identified lesion was identical to or contained within the ICEEG ictal onset in 13/15 (87%, examples shown in Figure 2, with red contacts indicating ICEEG ictal onset). Complete resection of the 7T-identified lesion was associated with seizure freedom (p=0.03). Histopathology of the 7T-identified lesions encountered mainly cortical dysplasia (FCD). In the 3T-lesional group, 7T detected additional smaller lesions in 19% (9/47) of patients (mostly with polymicrogyria/nodular heterotopia). 7T detected more lesions located in extratemporal than temporal lobes (p=0.002). In the 9 cases with FCD IIb, 5 (55%) were visible at 3T, and 8 (89%) were visible at 7T. In the 6 cases with FCD IIa, 3 (50%) were visible at 3T, and all (100%) were visible at 7T. In the 3 cases with mild malformation of cortical development with oligodendroglial hyperplasia (MOGHE), none (0%) were visible at 3T, and all (100%) were visible at 7T. In the 5 cases with mMCD II (including the double pathology case), 1 (1/5, 20%) was visible at 3T, and 2 (40%, 2/5) were visible at 7T. Conclusions: Our data showed that 7T may detect previously unseen subtle FCD in almost 50% of patients with negative 3T, and may provide improved delineation of the extent of pathology in the presence of 3T-visible lesions. MRI post-processing based on 7T significantly increases the yield for FCD detection. When concordant with the patient's electro-clinical profile, the additional 7T findings should be targeted in the devising of ICEEG implantation and resective/ablative surgical plans. Funding: This research was made possible by the JoshProvides Epilepsy Assistance Foundation Research Grant.