Role of Intraoperative Ultrasonography in Comparison with Early Postoperative MRI in Drug-Resistant Epilepsy Associated with Focal Cortical Dysplasia

Introduction: Surgery is the most effective treatment for cases of drug-refractory epilepsy associated with focal cortical dysplasia. Success of seizure outcomes depends on the extent of resection, while postoperative functional status is influenced by preservation of eloquent cortex. Therefore, accurately identifying and delineating focal cortical dysplasia (FCD) during surgery is crucial. This study seeks to evaluate the utility of intraoperative ultrasound in surgeries for FCD-associated drug-refractory epilepsy. Methods: We have a prospective study involving 27 patients experiencing drug-resistant epilepsy associated with radiologically suspected FCD who underwent epilepsy surgery at our institution, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, Karnataka, India, between June 2019 and October 2023. Findings of intraoperative ultrasonography (IOUS) were compared with those of presurgical magnetic resonance imaging (MRI) and the sonographic characteristics were analyzed in relation to the histopathological findings. Seizure outcome of postop patients was assessed using Engel grade. Results: IOUS detected residue in 5 cases after presumed end of resection. Resection was then continued in 4 of these 5 cases, to achieve complete resection. In 96.2% cases (26 patients), IOUS and intraoperative magnetic resonance/postop MRI had substantial agreement with respect to completion of resection and disagreed only in 3.7% cases (1 patient). Twenty-four patients are seizure-free postsurgery with average duration of follow-up being 41 months. One patient had rare nondisabling, nonhabitual seizures (Engel score 1d) and another patient had around one seizure per month with Engel score 3a. Conclusion: Morphological features of FCD, as identified by IOUS, correlated well with presurgical MRI. The appreciation of distinct sonographic features on IOUS allows the intraoperative differentiation between FCD and normal brain parenchyma. IOUS aids in more tailored and complete resections, thereby achieving seizure-free outcomes in majority of patients. IOUS is an easily accessible, portable, cost-effective tool that provides intraoperative localization of lesion, margin delineation, monitoring resection, and detection of residual lesion. Publication History Article published online: 15 July 2026 © 2026. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/) Thieme Medical and Scientific Publishers Private Limited A-13A, Graphix Tower 1, 6th floor, Sector 62, Noida 201309, Uttar Pradesh, India