The object of this study was to describe the utility and safety of using a single probe for combined intraoperative navigation and subcortical mapping in an intraoperative MR (iMR) imaging environment during brain tumor resection.
The authors retrospectively reviewed those patients who underwent resection in the iMR imaging environment, as well as functional electrophysiological monitoring with continuous motor evoked potential (MEP) and direct subcortical mapping combined with diffusion tensor imaging tractography.
As a navigational tool the monopolar probe used was safe and accurate. Positive subcortical fiber MEPs were obtained in 10 (83%) of the 12 cases. In 10 patients in whom subcortical MEPs were recorded, the mean stimulus intensity was 10.4 ± 5.2 mA and the mean distance from the probe tip to the corticospinal tract (CST) was 7.4 ± 4.5 mm. There was a trend toward worsening neurological deficits if the distance to the CST was short, and a small minimum stimulation threshold was recorded indicating close proximity of the CST to the resection margins. Gross-total resection (95%–100% tumor removal) was achieved in 11 cases (92%), whereas 1 patient (8%) had at least a 90% tumor resection. At the end of 3 months, 2 patients (17%) had persistent neurological deficits.
The monopolar probe can be safely implemented in an iMR imaging environment both for navigation and stimulation purposes during the resection of intrinsic brain tumors. In this study there was a trend toward worsening neurological deficits if the distance from the probe to the CST was short (< 5 mm) indicating close proximity of the resection cavity to the CST. This technology can be used in the iMR imaging environment as a surgical adjunct to minimize adverse neurological outcomes.