gms | German Medical Science

Objective: Navigated transcranial magnetic stimulation (nTMS) is a novel tool for preoperative functional planning. It combines a localized transcranial magnetic stimulation with a navigation system. In contrary to functional magnetic resonance imaging (fMRI) which outlines local metabolic changes, it is the only preoperative technique detecting highly functional cortical regions directly, comparable to direct cortical stimulation (DCS). Aim of the study was to evaluate the benefit of pre and intraoperative planning with nTMS and to correlate the results with fMRI.

Methods: 26 Patients between 2 and 78 years of age harbouring central lesions were tested with nTMS (NBS 4 Nexstim Finland) and fMRI preoperatively. Feasibility of the technique and localization of upper and lower limb cortical representation was compared. Intraoperative cortical mapping was performed using a navigated DCS probe and phase reversal (PR). Consistency of preoperative and intraoperative mapping was assessed via Brainlab Iplan navigation software.

Results: nTMS was feasible in 23 of 26 cases (88%). In two cases nTMS was not feasible due to referencing errors. In a two-year-old child no EMG could be elicited. fMRI could not be done in two children. No analyzable results were seen in 4 cases (15%): 3 due to inadequate compliance and in one patient with a rolandic AVM no assessable signal could be seen ipsilateral. Distinctive localisation was found in nTMS in 74% for hand and 65% for leg area while in fMRI in 80% for hand area and 65% for leg area. nTMS locations correlated with the fMRI location of eloquent motor areas in all cases. Intraoperatively location of Brodman area 4 with DCS and PR corresponded in all cases to preoperative nTMS stimulation area and fMRI localisation. In 6 cases for upper and in 8 cases for lower extremity preoperative nTMS showed positive responses in a wider area then primary motor cortex usually representing Brodman 6 (SMA). Central sulcus, respectively primary sensory cortex, could be discriminated in all cases.

Conclusions: nTMS via the NBS 4 NEXSTIM system is a helpful tool for preoperative planning. Compared with the fMRI, nTMS shows equivalent results in preoperative locating of central motor cortex. For paediatric patients and individuals who cannot perform standardized functional task in the fMRI, nTMS might be the only tool for preoperative functional planning. Pitfalls of nTMS are overstimulation especially in SMA and referencing errors.