Intraoperative stimulation mapping of thalamocortical tracts in asleep and awake settings: novel electrophysiological, anatomical, and tractographic paradigms

Despite the disabling deficits of motor apraxia and sensory ataxia resulting from intraoperative injury of the superior thalamocortical tracts (TCTs), region-specific electrophysiological localization is currently lacking. Herein, the authors describe a novel TCT mapping paradigm. Three patients, 1 asleep and 2 awake, underwent glioma resection affecting primarily the somatosensory cortex and underlying TCT. Stimulation was performed at the median, ulnar, and posterior tibial nerves. Parameters comprised single anodal pulses (duration 200-500 μsec, 2.1-4.7 Hz) with a current ranging from 10 to 25 mA. Recordings were captured with a bipolar stimulation probe, avoiding the classic collision technique. Positive localization sites were used to tractographically reconstruct the TCT in the third case. Employing one electrophysiological paradigm, the TCT was localized subcortically in all 3 cases by using a bipolar probe, peak range of 19.6-29.2 msec, trough of 23.3-34.8 msec, stimulation range of 10-25 mA. In the last case, tractographic reconstruction of the TCT validated a highly accurate TCT localization within a specific region of the posterior limb of the internal capsule. The authors describe the first electrophysiological technique for intraoperative localization and protection of the TCT in both asleep and awake craniotomies with tractographic validation, while avoiding the collision paradigm. None of the above paradigms have been previously reported. More data are required to further validate this technique.