Abstract

Objective: The recent FDA approval of the first 7T MRI scanner for clinical diagnostic use in October 2017 will likely increase the utilization of 7T for epilepsy presurgical evaluation. This study aims at accessing the radiological and clinical value of 7T in patients with pharmacoresistant focal epilepsy and 3T-visible lesions.Methods: Patients with pharmacoresistant focal epilepsy were included if they had a lesion on pre-operative standard-of-care 3T MRI and also a 7T research MRI. An epilepsy protocol was used for the acquisition of the 7T MRI. Prospective visual analysis of 7T MRI was performed by an experienced board-certified neuroradiologist and communicated to the patient management team. The clinical significance of the additional 7T findings was assessed by intracranial EEG (ICEEG) ictal onset, surgical resection, post-operative seizure outcome and histopathology. A subset of lesions were demarked with arrows for subsequent, retrospective comparison between 3T and 7T by 7 neuroradiologists using a set of quantitative scales: lesion presence, conspicuity, boundary, gray-white tissue contrast, artifacts, and the most helpful sequence for diagnosis. Conger's kappa for multiple raters was performed for chance-adjusted agreement statistics.Results: A total of 47 patients were included, with the main pathology types of focal cortical dysplasia (FCD), hippocampal sclerosis, periventricular nodular heterotopia (PVNH), tumor and polymicrogyria (PMG). 7T detected additional smaller lesions in 19% (9/47) of patients, who had extensive abnormalities such as PMG and PVNH; however, these additional findings were not necessarily epileptogenic. 3T−7T comparison by the neuroradiologist team showed that lesion conspicuity and lesion boundary were significantly better at 7T (p < 0.001), particularly for FCD, PVNH and PMG. Chance-adjusted agreement was within the fair range for lesion presence, conspicuity and boundary. Gray-white contrast was significantly improved at 7T (p < 0.001). Significantly more artifacts were encountered at 7T (p < 0.001).Significance: For patients with 3T-visible lesions, 7T MRI may better elucidate the extent of multifocal abnormalities such as PVNH and PMG, providing potential targets to improve ICEEG implantation. Patients with FCD, PVNH and PMG would likely benefit the most from 7T due to improved lesion conspicuity and boundary. Pathologies in the antero–inferior temporal regions likely benefit less due to artifacts.

Highlights

  • MRI plays an important role for the presurgical evaluation of patients with pharmacoresistant focal epilepsy

  • Radiological diagnosis based on the 3T MRI included 7 with unilateral hippocampal sclerosis (HS), 1 with bilateral hippocampal signal increase suspicious for HS, 1 with unilateral hippocampal signal/volume increase of uncertain etiology, nine with focal cortical dysplasia (FCD), one with FCD and HS, five with low-grade neoplasm, one with hippocampal cysts, two with cavernous malformation, two with DVA, one with DVA and FCD, seven with PVNH, five with PMG, four with chronic infarct, and one with tuberous sclerosis complex

  • Histopathology was reviewed in the 28 patients who underwent resective surgery with sufficient tissue; findings included four HS type I, one HS type II, four FCD type IIb, three FCD type IIa, one FCD IIIa, one FCD IIId, two PVNH, one cavernous malformation, one DNET grade I, one ganglioglioma grade I, 1 HS type I + FCD IIb, 1 HS type II + glial scars, 1 venous angioma

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Summary

Introduction

MRI plays an important role for the presurgical evaluation of patients with pharmacoresistant focal epilepsy. There have been a number of studies on structural 7T MRI in patients with pharmacoresistant focal epilepsy undergoing presurgical evaluation. These studies provided initial evidence that the improved signal-to-noise ratio from 7T MRI can lead to better detection/depiction of some epileptic lesions, such as focal cortical dysplasia (FCD), polymicrogyria (PMG), and vascular malformations [1,2,3,4,5,6,7,8,9,10]

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