A Pilot Feasibility Study of Neurodevelopmental Surveillance After the Fontan Operation Using a Sedation-Free Brain MRI Approach

Background and Objectives: After undergoing a Fontan operation, children with single-ventricle physiology are at a risk of neurodevelopmental impairment; data from the Korean population are scarce. We characterized the neurocognitive profiles of early school-aged Fontan patients and evaluated the feasibility of a sedation-free ultrafast brain magnetic resonance imaging (MRI) protocol for volumetric analysis. Methods: This prospective study screened 25 children who had undergone Fontan surgery and were in grades 1–3 (8–11 years of age) in 2023. After excluding children with a history of seizure, epilepsy, or brain infarction, 11 participants underwent standardized neurocognitive evaluation. Among them, four with extreme full-scale intelligence quotient (FSIQ) underwent 3T sedation-free ultrafast brain MRI (total scan time, 3 min 22 s), including volumetry-capable three-dimensional T1-weighted imaging. Six age-matched children served as controls. MRI volumetric analysis was exploratory and limited to a small subset of Fontan participants (n = 4), restricting statistical power and generalizability. Between-group comparisons were performed using Welch’s t-test, with Hedges’ g calculated as the effect size. Results: Mean FSIQ was 85.2 ± 24.3, with 36% patients with <85 FSIQ. Working memory (64%) and processing speed (55%) were most frequently impaired. Cerebellar volumes were lower in Fontan patients than in controls, although these differences were not statistically significant (left: 59.74 ± 8.86 vs. 72.26 ± 6.92 mL; right: 60.63 ± 7.70 vs. 71.54 ± 7.01 mL; very large effect sizes). Hippocampal volumes tended to be lower, and cerebellar volume showed a positive but non-significant correlation with processing speed. White matter hyperintensities and microbleeds were observed in two patients, both with impaired processing speed. Conclusions: School-aged Fontan patients exhibited selective deficits in working memory and processing speed, while exploratory MRI analysis suggested lower cerebellar volumes in the Fontan group. The ultrafast sedation-free MRI protocol proved feasible for volumetric assessment and, when combined with neurocognitive assessments, may support future milestone-based surveillance and early intervention for at-risk children.