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Abstracts

MRI-Negative Type II FCD as a Subtle Form of Bottom-of-Sulcus Dysplasia: Electrophysiological, Histopathological Evidence, and Treatment Implications

Abstract number : 1.302
Submission category : 4. Clinical Epilepsy / 4B. Clinical Diagnosis
Year : 2025
Submission ID : 1091
Source : www.aesnet.org
Presentation date : 12/6/2025 12:00:00 AM
Published date :

Authors :
Presenting Author: Weiyuan Luo, MD – Beijing Neurosurgical Institute, Capital Medical University, Beijing, China

Xiangzhi Lu, MD – Beijing Neurosurgical Institute, Capital Medical University, Beijing, China
Baotian Zhao, MD – Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
Chao Zhang, MD – Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
Xiu Wang, MD – Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
Jiajie Mo, MD – Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
Lin Sang, MD – Department of Neurosurgery, Beijing Fengtai Hospital, Beijing, China
Shan Song, MD – Department of Neurosurgery, Beijing Fengtai Hospital, Beijing, China
Xiaoqiu Shao, MD – Beijing Tiantan Hospital, Capital Medical University
Jianguo Zhang, MD – Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
Kai Zhang, MD – Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
Wenhan Hu, MD – Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China

Rationale: To determine whether MRI-negative type II focal cortical dysplasia (FCD) represents a subtle form of bottom-of-sulcus dysplasia (BOSD) based on electrophysiological, histopathological, and treatment evidence.

Methods: We retrospectively analyzed MRI-negative patients with histologically confirmed FCD type II who underwent resective epilepsy surgery between 2015 and 2025 at our center. All patients received SEEG monitoring, with at least one depth electrode traversing the dysplastic sulcus. Linear regression assessed the association between the distance from the sulcus bottom and standardized spike counts, high-frequency oscillation (HFO) counts, and epileptogenicity index (EI) values. Group comparisons were performed using the Mann–Whitney U test. Histopathological analyses were performed using H&E and immunohistochemistry for SMI32 and pS6, followed by visual and quantitative assessment of dysmorphic neurons (DNs). A separate cohort underwent MRI-guided laser interstitial thermal therapy (MRgLITT) targeting the sulcus bottom, and clinical outcomes were evaluated.

Results: SEEG recordings from 23 patients (132 contacts) showed significant negative correlations between the distance from the sulcus bottom and spike (R = –0.72), ripple (R = –0.66), fast ripple (R = –0.85) counts, and EI values (R = –0.64) (all P < .0001). Spike and HFO counts, as well as EI values, were significantly higher in bottom contacts than in non-bottom contacts (all P < .0001). Histopathological analysis of 10 patients revealed consistent enrichment of dysmorphic neurons (DNs) at the sulcus bottom. Immunostaining with SMI32 revealed significantly higher DN% in Segment 1 compared to Segments 2–5 (all pairwise Wilcoxon tests, P < .01). Similar patterns were observed with pS6 staining (P < .01), supporting the spatial concordance of DN accumulation across both markers. Among 19 patients who underwent MRgLITT targeting the sulcus bottom, mean ablation coverage was 28.3% ± 6.7%, with 73.7% achieving Engel IA outcomes. Transient deficits occurred in 21.1%, with no permanent complications.
Clinical Epilepsy