Introduction: Maximal surgical resection with the preservation of cortical functions is the treatment of choice for brain tumors. Achieving these objectives is especially difficult when the tumor is located in an eloquent area. Navigated transcranial magnetic stimulation (nTMS) is a modern non-invasive, preoperative method for defining motor and speech eloquent areas.
Material and methods: Patients with tumors located in motor and speech eloquent areas who presented at our institution between March 2017 and December 2017 were prospectively included. Exclusion criteria were frequent generalized epileptic seizures and cranial implants. For lesions involving motor eloquent areas we performed a nTMS motor mapping and for lesions involving speech eloquent areas we supplemented the motor mapping with speech and language mapping. MR images were exported from the nTMS system in a DICOM format and then loaded in the intraoperative neuronavigation system. Based on these findings, the optimal entry point and trajectory were determined, in order to achieve a maximum surgical resection of the lesion, while avoiding new postoperative neurological deficits.
Results: Nineteen patients underwent an nTMS brain mapping procedure between March 2017 and December 2017. In all cases a motor mapping procedure was done, but only in eight cases a speech mapping was also performed. Three patients presented new minor post-operatory deficits that consecutively remitted. The rest of the patients presented no added neurological deficits after surgery. In five cases the preexistent deficit was ameliorated after surgery and in three cases the deficit remitted. In one patient there was no improvement in the neurologic deficit after surgery.
Conclusion: nTMS is a reliable tool for the preoperative planning of eloquent area lesions. It must be taken into account that functional areas have a high individual variability. Therefore, knowing preoperatively the extent of the eloquent area helps the neurosurgeon adapt the surgical approach in order to obtain a better functional outcome.