Navigation-assisted subcortical mapping: intraoperative motor tract detection by bipolar needle electrode in combination with neuronavigation system.

Preservation of motor function is very important in patients who require resection of tumors adjacent to the primary motor cortex and pyramidal tract. Electrical stimulation of the tumor cavity is necessary to prevent postoperative neurological deterioration in these cases. A NY Tract Finder bipolar needle electrode which enabled the identification of motor pathways by inserting it into the white matter was developed and has been used. Recently, we developed a new electrode, NY Tract Finder II, which was modified for navigation-assisted detection of motor tract in cerebral white matter. Motor-evoked potentials were induced by electrical stimulation with this electrode when it was inserted toward the estimated motor pathway from the resected tumor cavity with guidance by a neuronavigation system. The scale on the needle indicated the approximate distance from the tumor cavity wall to the pyramidal tract. In conclusion, this technique may be a feasible method to detect and spare the motor pathways. However, further studies are needed to determine reliability and limitations.