Establishing language laterality: does resting-state functional MRI help?

OBJECTIVE Task-based functional MRI (tb-fMRI) is now considered the standard, noninvasive technique in establishing language laterality in children for surgical planning. The evaluation can be limited due to several factors such as age, language barriers, and developmental and cognitive delays. Resting-state functional MRI (rs-fMRI) offers a potential path to establish language dominance without active task participation. The authors sought to compare the ability of rs-fMRI for language lateralization in the pediatric population with conventional tb-fMRI used as the gold standard. METHODS The authors performed a retrospective evaluation of all pediatric patients at a dedicated quaternary pediatric hospital who underwent tb-fMRI and rs-fMRI from 2019 to 2021 as part of the surgical workup for patients with seizures and brain tumors. Task-based fMRI language laterality was based on a patient's adequate performance on one or more of the following: sentence completion, verb generation, antonym generation, or passive listening tasks. Resting-state fMRI data were postprocessed using statistical parametric mapping, FMRIB Software Library, and FreeSurfer as described in the literature. The laterality index (LI) was calculated from the independent component (IC) with the highest Jaccard Index (JI) for the language mask. Additionally, the authors visually inspected the activation maps for two ICs with the highest JIs. The rs-fMRI LI of IC1 and the authors' image-based subjective interpretation of language lateralization were compared with tb-fMRI, which was considered the gold standard for this study. RESULTS A retrospective search yielded 33 patients with language fMRI data. Eight patients were excluded (5 with suboptimal tb-fMRI and 3 with suboptimal rs-fMRI data). Twenty-five patients (age range 7-19 years, male/female ratio 15:10) were included in the study. The language laterality concordance between tb-fMRI and rs-fMRI ranged from 68% to 80% for assessment based on LI of independent component analysis with highest JI and for subjective evaluation by visual inspection of activation maps, respectively. CONCLUSIONS The concordance rates between tb-fMRI and rs-fMRI of 68% to 80% show the limitation of rs-fMRI in determining language dominance. Resting-state fMRI should not be used as the sole method for language lateralization in clinical practice.