Robot-assisted image-guided transcranial magnetic stimulation for somatotopic mapping of the motor cortex: a clinical pilot study

Abstract

PurposeShape and exact location of motor cortical areas varies among individuals. The exact knowledge of these locations is crucial for planning of neurosurgical procedures. In this study, we have used robot-assisted image-guided transcranial magnetic stimulation (Ri-TMS) to elicit MEP response recorded for individual muscles and reconstruct functional motor maps of the primary motor cortex.MethodsOne healthy volunteer and five patients with intracranial tumors neighboring the precentral gyrus were selected for this pilot study. Conventional MRI and fMRI were obtained. Transcranial magnetic stimulation was performed using a MagPro X100 stimulator and a standard figure-of-eight coil positioned by an Adept Viper s850 robot. The fMRI activation/Ri-TMS response pattern were compared. In two cases, Ri-TMS was additionally compared to intraoperative direct electrical cortical stimulation.ResultsMaximal MEP response of the m. abductor digiti minimi was located in an area corresponding to the “hand knob” of the precentral gyrus for both hemispheres. Repeated Ri-TMS measurements showed a high reproducibility. Simultaneous registration of the MEP response for m. brachioradialis, m. abductor pollicis brevis, and m. abductor digiti minimi demonstrated individual peak areas of maximal MEP response for the individual muscle groups. Ri-TMS mapping was compared to the corresponding fMRI studies. The areas of maximal MEP response localized within the “finger tapping” activated areas by fMRI in all six individuals.ConclusionsRi-TMS is suitable for high resolution non-invasive preoperative somatotopic mapping of the motor cortex. Ri-TMS may help in the planning of neurosurgical procedures and may be directly used in navigation systems.

Navigated transcranial magnetic stimulation for mapping the motor cortex in patients with rolandic brain tumors

“…The first-generation nTMS systems projected the midpoint of the stimulation coil orthogonally onto the underlying cortex. 6,10,11,13 This approach ignored the significant effect that the individual cortical anatomy, the tilting angle, and the rotation of the coil have on the resulting effective "e-field" distribution. The more recent studies were conducted with a system that projects the calculated e-field induced by the magnetic pulse onto a 3D model of the brain, which is locally fitted with up to 40,000 spheres for e-field modeling.…”

“…The next study 6 evaluated hotspots determined by nTMS and DES in 2 patients with brain tumors. In 1 patient the distance between hotspots was estimated at less than 5 mm, but in the other case the comparison referred to the distance between hotspots by preoperative nTMS and DES that was conducted after tumor removal.…”

“…3,4,6,[8][9][10][11]13,14,21 A total of 199 attempts in 161 patients to identify the motor cortex using nTMS were described. In only 1 patient, who had an infiltrating glioma within the somatosensory cortex, could TMS not identify any motor site.…”

“…Although TMS was introduced in clinical neurology in 1985, 1 its use in neurosurgery has been sporadic, and only recently an increasing number of reports from neurosurgical institutions on the use of nTMS for brain mapping in patients with rolandic brain tumors have been published. 3,4,6,[8][9][10][11]13,14,21 In the present article, based on a review of previous reports evaluating the spatial accuracy of nTMS in comparison with the gold standard of DES and/or assessing the clinical impact of the method, we address the clinical utility of nTMS in rolandic brain tumor surgery. …”

Avaliação da estimulação magnética transcraniana navegada no mapeamento anatômico e funcional não invasivo do córtex motor

“…Estudos em córtex de humanos e símios mostraram que a corrente espalha-se por, no máximo, 2 a 3 mm do ponto estimulado, sem provocar qualquer alteração histológica permanente (Berger et al,1990 (Vitikainen et al, 2009). No entanto, em um estudo de mapeamento assistido por robô, um dos cinco pacientes com um tumor encefálico cortical desenvolveu uma crise convulsiva focal durante o mapeamento com EMT (Kantelhardt et al, 2010).…”