The role of ultra-high field MRI and image processing in the presurgical workup in MRI-negative focal epilepsy: A validated 7T MRI case study

Abstract

This case study demonstrates the value of combined 7 T structural and functional MRI in the presurgical workup of a 24-year-old male with drug-resistant focal epilepsy who was initially considered MRI-negative on clinical 3 T MRI. The patient underwent extensive presurgical workup with 7 T MRI, magnetoencephalography, stereo-electroencephalography, and resection of the suspected right frontal epileptogenic zone. Histopathology showed focal cortical dysplasia (FCD) type IIb. The patient remained 11 months after surgery seizure-free. Retrospective analysis revealed that both structural and functional 7 T MRI showed abnormalities within the resected area. Morphometric Analysis Program (MAP18) detected abnormalities on both 3 T and 7 T images. However, abnormalities were more conspicuous on 7 T. Resting-state functional MRI metrics, particularly regional homogeneity and fractional amplitude of low-frequency fluctuations, demonstrated significantly increased values in both a MAP18-defined region of interest and the entire resected area compared to a healthy control group (p < 0.05). However, extensive unspecific abnormalities were also observed outside the resected region, highlighting the importance of a multimodal approach. This case study illustrates that advanced image processing of ultra-high field structural and resting-state functional MRI scans may enhance the detection of subtle epileptogenic lesions in presurgical evaluation, potentially improving post-operative seizure outcome and associated quality of life.

Keywords: 7T MRI; Focal cortical dysplasia; MAP18; ReHo; Resting-state fMRI; Voxel-based morphometry; fALFF.

Fig. 1

Visualization of the patient’s presurgical trajectory. NPE: neuropsychological evaluation; GTC: generalized tonic-clonic seizures; EEG: electroencephalography; FDG-PET: fluorodeoxyglucose positron emission tomography; MEG: magnetoencephalography; SEEG: stereo-EEG; ECoG: electrocorticography; FCD: focal cortical dysplasia; ILAE: International League Against Epilepsy.

Fig. 2

A: Visualization of the 3 T FLAIR with overlayed depth electrode positioning using MIND and DENSE (CNSprojects, Amsterdam) . Only electrodes involved in the seizure onset are visualized, with the most prominent contacts highlighted – red circle indicates main seizure onset; light blue circle indicates minor seizure onset (i.e. not always involved directly at the seizure onset). B: delineation (purple contour) of the resected area overlaying the post-SEEG 3 T FLAIR. C: magnification (yellow box) of the electrode placement in transverse plane. The 3 T FLAIR sequence was used for both the electrode placement planning and the delineation of the resection area. D: post-resection 3 T FLAIR image. E,F: histological images of the resected specimen showing a balloon cell (E – black arrow) and dysmorphic neurons (F – yellow arrows). FLAIR: fluid-attenuated inversion recovery image. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

A: Morphometric MAP18 combined z-score maps for both 3 T and 7 T, with the delineation of the resected area (red contour). B: rs-fMRI z-score maps with the resected area (red contour) and the MAP18-defined FCD region (yellow contour) outlined. C: Comparison between the median values (plotted on y-axis) from the respective regions of interest, from only those metrics where the patient’s value was significantly abnormal with respect to the controls. * marks p < 0.05; ** marks p < 0.01. T1w: T1-weighted; MAP18: Morphometric Analysis Program; rs-fMRI: resting-state functional MRI; ReHo: regional homogeneity; ALFF: amplitude of low-frequency fluctuations; fALFF: fractional ALFF; FCD: focal cortical dysplasia. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)