Fig. 2.

Case with discordance between pre-operative DT and intraoperative stimulation. A 41-year-old right handed man on imaging surveillance for a known IDH mutated astrocytoma. Although an island of white matter and sparse ‘tracts’ were visible within this heterogeneous transforming lesion, pre-operative diffusion tractography (DT) did not convincingly identify the inferior fronto-occipital fasciculus running through the tumor, even at a reduced fractional anisotropy tracking threshold (0.17). However, subcortical stimulation during awake surgery elicited semantic paraphasias and naming errors at this location, indicating an eloquent IFOF. The patient experienced transient slight language deterioration affecting naming and repetition