gms | German Medical Science

Objective: There is an increasing number of neurosurgical departments applying navigated transcranial stimulation (nTMS) in the preoperative assessment of patients with tumors in motor eloquent areas. While traditional nTMS mapping shows remarkable results in identifying cortico-spinal connectivity, it has drawbacks in detecting cortical network integrity. The combination of nTMS with high-density electroencephalographic recordings (TMS-EEG) opens a new window to the perioperative functional evaluation of cortical network processes and their impairment by tumors or neurosurgical interventions. In the present study, we report our experience with TMS-EEG in patients with tumors in motor eloquent areas.

Method: The presented study enrolls 12 consecutive patients scheduled for microsurgical resection of tumors in motor eloquent areas. All patients underwent a preoperative nTMS mapping followed by a TMS-EEG examination with 128-channel EEG. The cortical motor network was evaluated by the time-locked EEG responses after individual TMS pulses (cortical-evoked potentials, CEP) and their spectral representations. Electrophysiological results were compared to the motor performance assessed by the Medical Research Council Scale (MRCS) and the Purdue Pegboard-Test.

Results: CEPs after nTMS were detected in 75% of the patients projecting to the premotor areas such as the supplementary motor area (SMA). There were significant individual differences in shape and amplitude of the CEPs. However, there was a good correlation between electrophysiological results and the motor performance as measured by the Purdue Pegboard-Test.

Conclusions: The first TMS-EEG evaluations of neurosurgical patients suggest CEPs as an electrophysiological marker for motor network integrity correlating with the factual motor performance. Hence, TMS-EEG could provide a new tool for the perioperative functional evaluation of patients predicting new postoperative deficits such as the SMA syndrome.