前頭斜帯路の切断：非英語圏の脳卒中生存者における言語開始障害のネットワーク証拠

The frontal aslant tract (FAT) is a direct cortico-cortical intra-frontal pathway linking the inferior frontal gyrus with the pre-supplementary and supplementary motor areas and is implicated in speech initiation and verbal fluency. However, much of the available evidence regarding its role in speech production derives from studies in English-speaking populations, which may limit the generalizability of these findings to underrepresented languages and linguistic contexts.

We report a 74-year-old Arabic-speaking man who developed acute non-fluent aphasia following a left frontal infarct. Neurological examination demonstrated near-complete speech arrest with relative preservation of receptive language abilities and orofacial praxis, and without limb weakness. MRI localized the lesion to the pars opercularis/middle frontal junction, and diffusion tensor imaging demonstrated focal discontinuity of the left FAT with preservation of the right homolog. Confrontation naming could not be assessed due to the complete absence of verbal output. This clinical-anatomical dissociation, marked impairment of speech initiation in the context of relatively preserved receptive and buccofacial motor functions, supports a critical role of the left FAT in initiating propositional speech.

This case provides tract-level evidence that selective FAT disruption can result in profound deficits in speech initiation while sparing posterior language networks, reinforcing network-based models of language production. These findings underscore the importance of anatomically informed and linguistically inclusive diagnostic and rehabilitation approaches for non-Anglophone populations.