First United Kingdom Experience of Navigated Transcranial Magnetic Stimulation in Preoperative Mapping of Brain Tumors

Abstract

Surgery for lesions in eloquent brain areas remains challenging owing to the risk of permanent neurological deficits. To date, direct electrical stimulation (DES) and intraoperative neuromonitoring represent the reference standard. Recently, navigated transcranial magnetic stimulation (nTMS) has emerged as a mapping tool to optimize surgical planning. Our aim was to correlate nTMS with the intraoperative findings and assess its effects on surgical decision-making. We retrospectively reviewed our series of patients who had undergone craniotomy for removal of a brain tumor at our institution with preoperative nTMS, intraoperative neuromonitoring, and DES from February 2017 to February 2018. Demographic data, tumor entity and location, extent of resection, change in surgical approach, and neurological outcome were collected. Of 35 patients, 24 (68.6%) had undergone preoperative motor mapping and 11 (31.4%) had undergone mapping for language. Histopathological examination demonstrated glioma in 88.6% (high grade, n= 24; low grade, n= 6), metastasis (n= 2), epidermoid cyst (n= 1), and cavernoma (n= 1). nTMS resulted in change in the surgical strategy in 31.5% (craniotomy size, n= 7; access pathway, n= 3; surgical indication, n= 1). The specificity of nTMS for language was 66.7%, with a negative predictive value of 74.1%. nTMS motor mapping correlated with DES in all cases, with a mean abductor pollicis brevis hotspot distance of 3.50 ± 0.66 mm (n= 9). nTMS is a safe, noninvasive adjunctive tool for preoperative mapping of brain tumors in eloquent areas. Furthermore, nTMS can influence the surgical decisions in up to one third of patients in our experience.