gms | German Medical Science

Objective: Preoperative mapping of the brain surface to identify eloquent cortical regions is a developing area in neurosciences. The combination of transcranical magnetic stimulation (TMS) and neuronavigation (nTMS) yields the promise of a new non-invasive cortical mapping tool. Aim of our feasibility study was to assess the accuracy of a novel nTMS device in healthy subjects and patients with intracranial lesions.

Methods: A neuronavigation system (BrainLAB) was reprogrammed to enable the tracking of a TMS coil (Magstim) and to display the stimulation site on the cortex. The motor cortex of eleven healthy subjects were mapped using the nTMS system. The centre of gravity(CoG) of the cortical representation of 8 muscle was calculated. Subsequently the sulcus centralis (sc) and the hand knob were determined. The distance of these muscle CoGs from the sc was calculated. The hand knob as established by the nTMS mapping was compared to the neuroanatomical location estimated by 4 clinicians (3 neuroradiologists, 1 neurosurgeon). In addition, two patients with low grade gliomas in the vicinity of the rolandic fissure were mapped preoperatively. Those maps were compared to the results of the intraoperatively performed direct cortical stimulation.

Results: The distances of the muscle CoGs to sc ranged between 3,0 to 4,1 mm (mean 3,5 mm ±5,8 SD). The accordance between classical neuroanatomical location and nTMS mapping for the hand knob ranged between 79 to 81%. The comparison between intraoperative direct cortical stimulation and nTMS data in two patients showed excellent concordance in both cases.

Conclusions: Our feasibility study showed a high accuracy and reproducibility of nTMS data thus making this method suitable for motor cortex mapping. However, further improvements in computerisation are needed to reduce the time and human resources needed for the mapping procedure.