Mirrored structural symmetry index (VMSSI): a novel approach for diagnosing MR-negative focal cortical dysplasia using structural MRI

BackgroundFocal cortical dysplasia (FCD) is a common cause of drug-resistant epilepsy, yet its diagnosis remains challenging, particularly for magnetic resonance imaging (MRI)-negative FCD. In this study, we propose a novel metric, the Voxel-Mirrored Structural Symmetry Index (VMSSI), to quantify hemispheric structural symmetry using T1-weighted MRI.MethodsA total of 104 patients with suspected FCD and 104 age and sex matched healthy controls from two centers were enrolled, and their brain images were mirrored along the longitudinal axis to create a dataset. The diagnostic discriminatory ability of magnetic resonance signal intensity value symmetry, cortical thickness symmetry and VMSSI was further verified by subject receiver operating characteristic (ROC) curve analysis. The sensitivity and specificity were used to assess the performance of VMSSI at different diagnostic thresholds.ResultsThe cortical thickness symmetry index (MeanThicknessDiff) was significantly different between the two groups (p < 0.001). The values of the combined symmetry index were significantly higher in the MR-negative FCD patient group than in the healthy control group (p < 0.001). The area under the curve (AUC) of VMSSI was 0.80 (95% CI: 0.72, 0.88).VMSSI exhibited 77% sensitivity and 85% specificity at the optimal thresholds of 3.4.ConclusionThese results demonstrate that VMSSI is a reliable and effective tool for detecting MR- negative FCD, providing a quantitative structural biomarker that may aid in improving diagnostic accuracy in clinical practice.