Navigated transcranial magnetic stimulation mapping in patients with language-eloquent brain lesions

Introduction: The surgical resection of brain lesions located in language-eloquent areas harbours a great risk for determining new functional deficits. Navigated transcranial magnetic stimulation represents a novel non-invasive cortical mapping method that can be used preoperative to determine language-eloquent areas. Materials and methods: We retrospectively reviewed a prospectively maintained database of patients that underwent preoperative cortical mapping using nTMS between March 2017 and June 2020. Patients older than 18 years old with brain lesions situated in a presumed language eloquent area, that underwent surgical resection of the brain lesion were included in the study. Various parameters such as error rate, number of language-negative sites were assessed. Results: Fourteen patients were included in the study. There were 10 males and 4 females in total. Most of the tumours were in the temporal and frontal lobes (five and four cases, respectively). The histopathological diagnosis was glioblastoma in seven cases, in one case there was an anaplastic astrocytoma and there were two cases of low-grade gliomas. There were three cases of brain metastasis and one cavernoma. The median (range) tumor volume was 25.01 cm3 (0.89 – 86.55 cm3). Gross-total resection (GTR) was achieved in seven cases. The error rate was significantly higher in patients that continued to have an impaired language function after surgical resection (p = 0.016), while the perilesional error rate was higher in patients with preoperative aphasia (p = 0.019). Conclusion: Our findings suggest that a lower tumour volume to perilesional negative stimuli ratio is associated with an extended surgical resection of brain tumours located in language-eloquent areas and that patients that presented with aphasia and have a high error rate have a worse functional prognosis. Through nTMS preoperative cortical mapping of language-eloquent areas, the neurosurgeon has more insight regarding the cortical function and can maximize the surgical resection, while avoiding the onset of new functional deficits.