Localization of the Epileptogenic Zone by Multimodal Neuroimaging and High-Frequency Oscillation.

Xiaonan Li,Wei Wang,Zhiwei Ren,Guojun Zhang,Xin Chen,Yue Xing,Horace H Loh,Tao Yu,Xiaoming Yan,Xianchang Zhang,Xiaofeng Yang,Jiaqing Yan,Herui Zhang,Xueyuan Wang

doi:10.3389/fnhum.2021.677840

Abstract

Accurate localization of the epileptogenic zone (EZ) is a key factor to obtain good surgical outcome for refractory epilepsy patients. However, no technique, so far, can precisely locate the EZ, and there are barely any reports on the combined application of multiple technologies to improve the localization accuracy of the EZ. In this study, we aimed to explore the use of a multimodal method combining PET-MRI, fluid and white matter suppression (FLAWS)—a novel MRI sequence, and high-frequency oscillation (HFO) automated analysis to delineate EZ. We retrospectively collected 15 patients with refractory epilepsy who underwent surgery and used the above three methods to detect abnormal brain areas of all patients. We compared the PET-MRI, FLAWS, and HFO results with traditional methods to evaluate their diagnostic value. The sensitivities, specificities of locating the EZ, and marking extent removed versus not removed [RatioChann(ev)] of each method were compared with surgical outcome. We also tested the possibility of using different combinations to locate the EZ. The marked areas in every patient established using each method were also compared to determine the correlations among the three methods. The results showed that PET-MRI, FLAWS, and HFOs can provide more information about potential epileptic areas than traditional methods. When detecting the EZs, the sensitivities of PET-MRI, FLAWS, and HFOs were 68.75, 53.85, and 87.50%, and the specificities were 80.00, 33.33, and 100.00%. The RatioChann(ev) of HFO-marked contacts was significantly higher in patients with good outcome than those with poor outcome (p< 0.05). When intracranial electrodes covered all the abnormal areas indicated by neuroimaging with the overlapping EZs being completely removed referred to HFO analysis, patients could reach seizure-free (p < 0.01). The periphery of the lesion marked by neuroimaging may be epileptic, but not every lesion contributes to seizures. Therefore, approaches in multimodality can detect EZ more accurately, and HFO analysis may help in defining real epileptic areas that may be missed in the neuroimaging results. The implantation of intracranial electrodes guided by non-invasive PET-MRI and FLAWS findings as well as HFO analysis would be an optimized multimodal approach for locating EZ.

Highlights

For patients with drug-refractory epilepsy, surgical removal of the epileptogenic zone (EZ), which is defined as the brain regions necessary and sufficient for initiating seizures (Rosenow and Luders, 2001), is the best option to eliminate seizures (Jacobs et al, 2010)
Comparing Results Obtained by New Techniques With Those Obtained by Traditional Methods As some traditional inspection methods like MRI, scalp EEG, and intracranial EEG are widely used clinically, it is necessary to compare their results pertaining to the detection of suspicious epileptic areas with those of new techniques such as PET-MRI, fluid and white matter suppression (FLAWS), and high-frequency oscillation (HFO), to evaluate the diagnostic value
For patients with a good outcome, each patient’s brain area could be regarded as two parts: one part was the area marked by the method and eventually removed which must belong to the EZ; the other part was the remaining area, which must be inside the non-EZ

Summary

Introduction

For patients with drug-refractory epilepsy, surgical removal of the epileptogenic zone (EZ), which is defined as the brain regions necessary and sufficient for initiating seizures (Rosenow and Luders, 2001), is the best option to eliminate seizures (Jacobs et al, 2010). PET imaging provides important insights into the functional integrity and activity of neural systems, as it is a sensitive and non-invasive method for measuring brain metabolism. Developed PET and MRI coregistration approaches combined the tissue contrast of MRI and the metabolic characterization of FDG-PET, which would help to delineate surgical resection margins correlated with the structural anatomy and improve surgical outcomes based on discernible MRI findings (Salamon et al, 2008). Hybrid PET/MR scanners could combine the superior soft tissue contrast of MRI and the metabolic characterization of FDG-PET into a single exam without the need for the additional ionizing radiation inherent to PET/CT systems (Paldino et al, 2017), further promoting its clinical usage

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