Figure 2 Patient No 4 had a left fronto‐parietal glioblastoma multiforme. (A) Preoperative fibre‐tracking identified symmetrical pyramidal tracts (red lines) from the cortex to the cerebral peduncles. (B) Brain T2 weighted MRI revealed a hyperintense area in close proximity to the left pyramidal tract, identified by fibre‐tracking (red). Cortical stimulation of the left precentral gyrus, which had been defined by a somatosensory evoked potential, elicited a motor evoked potential (MEP) in the right abductor pollicis brevis muscle (Cortex). During removal of the tumour, subcortical stimulation elicited MEPs at the bottom of the tumour (intersection of the yellow lines in the intraoperative navigation image), 1 cm from the edge of the predicted pyramidal tract (red) (Subcortex). To avoid causing additional neurological deficits, no further removal was performed. (C) Postoperative T2 weighted MRI demonstrated preservation of the pyramidal tracts identified by fibre‐tracking (red).