The role of navigated transcranial magnetic stimulation for surgery of motor-eloquent brain tumors: a systematic review and meta-analysis

Navigated transcranial magnetic stimulation (nTMS) is an emerging tool for surgery of motor-eloquent intrinsic brain tumors, but a critical reappraisal of the literature evidence has never been performed, so far. A systematic review and meta-analysis was performed searching on PubMed/MEDLINE, and the Cochrane Central Register of Controlled Trials for studies that analyzed the impact of nTMS-based motor mapping on surgery of patients affected by motor-eloquent intrinsic brain tumors, in comparison with series of patients operated without using nTMS. The impact of nTMS mapping was assessed analyzing the occurrence of postoperative new permanent motor deficits, the gross total resection rate (GTR), the size of craniotomy and the length of surgery. Only eight studies were considered eligible and were included in the quantitative review and meta-analysis. The pooled analysis showed that nTMS motor mapping significantly reduced the risk of postoperative new permanent motor deficits (OR = 0.54, p = 0.001, data available from eight studies) and increased the GTR rate (OR = 2.32, p < 0.001, data from seven studies). Moreover, data from four studies documented the craniotomy size was reduced in the nTMS group (-6.24 cm2, p < 0.001), whereas a trend towards a reduction, even if non significant, was observed for the length of surgery (-10.30 min, p = 0.38) in three studies. Collectively, currently available literature provides data in favor of the use of nTMS motor mapping: its use seems to be associated with a reduced occurrence of postoperative permanent motor deficits, an increased GTR rate, and a tailored surgical approach compared to standard surgery without using preoperative nTMS mapping. Nonetheless, a growing need of high-level evidence about the use of nTMS motor mapping in brain tumor surgery is perceived. Well-designed randomized controlled studies from multiple Institutions are clearly advocated to continue to shed a light on this emerging topic.