Brain Microstructural Alterations in Children with Tuberous Sclerosis Complex: A Neurite Orientation Dispersion and Density Imaging Study

Objective: To evaluate brain microstructural alterations in children with tuberous sclerosis complex (TSC) using neurite orientation dispersion and density imaging (NODDI) and to investigate associations between NODDI parameters and clinical phenotypes including epilepsy, early-onset epilepsy, infantile epileptic spasms, status epilepticus, and drug-resistant epilepsy. Methods: This prospective cross-sectional study enrolled 68 children with TSC and 39 healthy controls (sex-matched; the groups differed significantly in age, which was adjusted for in all analyses, with spline modeling and pediatric-range sensitivity analyses) who underwent multi-shell diffusion MRI. NODDI parameters neurite density index (NDI), orientation dispersion index (ODI), and isotropic volume fraction (FISO) were computed. Group differences were assessed using Mann–Whitney U tests, with additional analyses adjusting for age. Logistic regression examined associations between NODDI parameters and clinical variables. Receiver operating characteristic analysis evaluated discriminative performance within the derivation cohort, with bootstrap and cross-validated internal validation. Results: The TSC group demonstrated significantly reduced whole-brain NDI, ODI, and FISO compared to controls after adjusting for age (all p ≤ 0.001). TSC patients with epilepsy showed significantly lower NDI (p < 0.001), ODI (p = 0.001), and FISO (p = 0.003) versus controls, whereas patients without epilepsy showed no significant differences. Early-onset epilepsy and infantile epileptic spasms were associated with marked NDI reductions (16.7% and 19.0%, respectively; p < 0.001). In a parsimonious model, NDI was associated with epilepsy (p = 0.008; bootstrap-corrected AUC 0.712); in an exploratory multivariable model, NDI (p = 0.008) and ODI (p = 0.035) were associated with epilepsy after adjustment. NDI achieved an AUC of 0.739 (95% CI 0.617–0.861) with 65.5% sensitivity and 78.8% specificity at a cutoff of 0.095, reflecting discrimination within the derivation cohort. Conclusions: NODDI sensitively detects widespread brain microstructural alterations in children with TSC. NDI, and to a lesser extent ODI after adjustment, show significant associations with epilepsy and may serve as quantitative imaging markers of epilepsy-associated microstructural burden; however, the cross-sectional design cannot establish whether these alterations are caused by epilepsy or reflect the underlying TSC disease process, and whether they predict future epilepsy onset or outcome requires longitudinal, externally validated studies. The significant age difference between groups, which statistical adjustment cannot fully resolve, is a key limitation. NODDI is best viewed as one component of a multimodal biomarker framework that also incorporates molecular, immune and electrophysiological measures.