How an expert glioma surgeon thinks about preoperative nTMS for the planning of surgery in motor-eloquent glioma – A survey of 90 consecutive cases

<h2>Abstract</h2><h3>Objective</h3> Direct electric stimulation (DES) is the gold standard for identifying cortical and subcortical regions with motor eloquence. However, DES can only be applied intraoperatively, after craniotomy, and therefore cannot be used to guide pre-operative management. Currently, there is no consensus on a gold standard for preoperative evaluation of eloquent brain areas, with surgeons relying on a multi-modal strategy to guide surgical resection. This study aims to define the role of navigated transcranial magnetic stimulation (nTMS) in surgical planning, as employed by an expert glioma surgeon. <h3>Methods</h3> An experienced glioma surgeon completed a structured questionnaire regarding the visualization of motor-eloquent brain areas and surgical access planning before and after viewing nTMS motor mapping data in the process of presurgical planning. <h3>Results</h3> A consecutive series of 90 patients with suspected glioma adjacent to the motor cortex undergoing presurgical nTMS motor mapping was analyzed. Motor-evoked potentials were obtained in 89 cases (98.9%). The relationship between the tumor and motor-eloquent brain areas was rated as "well" or "perfectly" in 8 cases (8.9%) before and in 28 cases (31.1%) after nTMS motor mapping. A high probability of altering the current surgical plan intraoperatively after DES was noted in 8 cases (8.9%) before and 18 cases (20%) after nTMS. In addition, the number of patients with a high certainty of not changing the surgical plan increased from 6 cases (6.7%) to 24 cases (26.7%) after nTMS. nTMS data led to a different surgical strategy regarding the size and/or location of the craniotomy in 35 cases (38.9%), the corticotomy in 33 cases (36.7%), and the surgical corridor in 36 cases (40%). nTMS data impacted patient consultation in 28 cases (31.1%). Overall, the addition of nTMS motor mapping to the pre-operative process conferred a positive impact in 46 cases (51.1%). <h3>Conclusions</h3> nTMS motor mapping has a major perceived impact on surgical planning for motor-eloquent gliomas, as well as on patient consultation, in the view of a highly experienced glioma surgeon.