gms | German Medical Science

Objective: The aim of this study is to analyze the impact of the introduction of navigated TMS (nTMS) in the preoperative evaluation of patients with eloquently located low-grade gliomas (LGG).

Methods: This paper reports on 22 patients with LGGs involving the primary motor cortex treated at our institution. 11 patients received preoperative nTMS mapping, the other 11 were treated before the introduction of nTMS. Both groups were well matched in terms of tumor and patient characteristics. The extent of resection, functional outcome, time to progression, seizure control and the need for postoperative radio or chemotherapy were evaluated.

Results: In the nTMS group the solid tumor mass (hypointense T1) was totally resected in 9 cases. In six cases, the area of altered MRI FLAIR signal clearly exceeded the T1 hypodense tumor area, and nTMS showed that this area harboured motor function in five cases. This excess FLAIR zone was resected to the functional limit in 4 cases and totally in 1 case. Two patients suffered a loss of motor strength that persisted beyond discharge but was recovered by 3 month follow-up. In the pre-nTMS group no complete resection was performed. 3 patients had an incomplete resection, 5 of the remaining 8 had a biopsy followed by a watch and wait policy and 3 cases had no surgery. The more conservative approach in the pre-nTMS group led to significantly earlier tumor progress and increased need for radio and chemo therapy.

Conclusions: The demonstration of no motor function within the tumor greatly facilitates the decision for a more aggressive treatment approach with minimal morbidity in LGGs located within the primary motor cortex. Intraoperative mapping especially subcortically certainly is still mandatory.