Infiltration of the basal ganglia by brain tumors is associated with the development of co-dominant language function on fMRI

•We investigated anatomical factors influencing hemispheric language dominance.•Basal ganglia involvement by tumor was correlated with co-dominance (p < 0.001).•Insula and precentral gyrus may also play roles in plasticity of language network.•Involvement of Broca’s and Wernicke’s areas did not correlate with co-dominance.•Interhemispheric reorganization of language may confer behavioral advantages.

Studies have shown that some patients with left-hemispheric brain tumors have an increased propensity for developing right-sided language support. However, the precise trigger for establishing co-dominant language function in brain tumor patients remains unknown. We analyzed the MR scans of patients with left-hemispheric tumors and either co-dominant (n = 35) or left-hemisphere dominant (n = 35) language function on fMRI to investigate anatomical factors influencing hemispheric language dominance. Of eleven neuroanatomical areas evaluated for tumor involvement, the basal ganglia was significantly correlated with co-dominant language function (p < 0.001). Moreover, among patients whose tumors invaded the basal ganglia, those with language co-dominance performed significantly better on the Boston Naming Test, a clinical measure of aphasia, compared to their left-lateralized counterparts (56.5 versus 36.5, p = 0.025). While further studies are needed to elucidate the role of the basal ganglia in establishing co-dominance, our results suggest that reactive co-dominance may afford a behavioral advantage to patients with left-hemispheric tumors.