gms | German Medical Science

Objective: There is increasing evidence that preoperative functional evaluation by navigated transcranial stimulation (nTMS) improves clinical outcome of patients with tumors in motor eloquent areas. At the same time, there is an increasing application of intraoperative techniques such as intraoperative neuromonitoring (IOM) and intraoperative magnetic resonance imaging (iMRI), which in contrast to nTMS provide direct feedback to the neurosurgeon concerning functional status and residual tumor that should be removed. The presented study aims to evaluate the possible role of nTMS in an operating environment including IMRI and IOM.

Method: The presented retrospective study enrolled 34 consecutive patients scheduled for resection of astrocytomas of the central motor region in the intraoperative MRI suite (iMRI) together with intraoperative neuromonitoring (IOM) of motor-evoked potentials (MEP) to the upper and lower extremities. While 16 patients received functional imaging with navigated transcranial magnetic stimulation (nTMS) one day prior to operation (nTMS-iMRI group), 18 patients underwent surgery without any further preoperative functional assessment (iMRI group). All of these patients received an intraoperative MRI scan. The necessity of a re-resection after the intraoperative control scan was taken as a baseline to evaluate the operative outcome.

Results: In 56% of the cases in the nTMS-iMRI group (9/16), surgery was finished after the first intraoperative scan. In eight cases (50%) iMRI showed a complete tumor resection, in one case surgery was terminated although iMRI revealed residual tumor due to worsening of motor-evoked potentials during IOM. In 44% surgery had to be continued to achieve complete tumor resection. In the iMRI group without preoperative nTMS evaluation, surgery was finished in 28% of the cases (5/18) after the first intraoperative scan. In 72% surgery was continued in order to achieve complete tumor resection. In one case surgery was terminated because motor-evoked potentials worsened.

Conclusions: These results suggest that preoperative nTMS evaluation increases the neurosurgeon’s confidence during tumor surgery in motor eloquent areas despite the presence of iMRI and IOM. Hence, preoperative nTMS might help to reduce operating time in an iMRI environment. Subsequently, preoperative nTMS might increase the extent of resection by visualization of functional anatomy before surgery in centres without intraoperative MRI control.