Navigated Brain Stimulation (NBS) by Nexstim, is the only CE marked and FDA cleared noninvasive solution to presurgical mapping of the motor cortex. The NBS System 5 adds navigation to transcranial magnetic stimulation (nTMS), creating a precise map of the eloquent cortex superimposed on a patient specific MRI.
NBS accurately locates the stimulating electric field (E-field) in the cortex, with the proven accuracy of direct cortical stimulation (DCS)1. The stereotactic camera provides visualization of the induced E-field, which is displayed in a 3D rendering of the individual patient’s MRI. Placing surface electrodes on the desired muscles, the 6-channel EMG records motor evoked potentials (MEPs) amplitudes and latencies. As the TMS coil is moved over the patient’s head, the operator can see, in real-time, the E-field location, strength and direction in the 3-D intracranial rendering, creating a map of the cortical somatotopy.
The patient’s motor responses are clearly marked as pegs color coded as a heat scale. Each mapping session can be stored to precisely replicate any session at a later date. The NBS System’s mapping results can be exported via DICOM to planning systems or directly into the neuronavigator. In the OR, Navigated Brain Stimulation maps help optimal placement of DCS electrodes and facilitates surgical guidance.
Introduction: Transcranial magnetic stimulation (TMS) is increasingly used for non-invasive functional mapping in preoperative evaluation for brain surgery, and the reliability of navigated TMS (nTMS) motor representation maps has been studied in the healthy population and in brain tumor patients. The lesions behind intractable epilepsy differ from typical brain tumors, ranging from developmental cortical malformations to injuries early in development, and may influence the functional organization of the cortical areas. Moreover, the interictal cortical epileptic activity and antiepileptic medication may affect the nTMS motor threshold. The reliability of the nTMS motor representation localization in epilepsy patients has not been addressed.
Methods: We compared the nTMS motor cortical representation maps of hand and arm muscles with the results of invasive electrical cortical stimulation (ECS) in 13 patients with focal epilepsy. The nTMS maps were projected to the cortical surface segmented from preoperative magnetic resonance images (MRI), and the positions of the subdural electrodes were extracted from the postoperative low-dose computed tomography (CT) images registered with preoperative MRI.
Results: The 3D distance between the average nTMS site and average ECS electrode location was 11 ± 4 mm for the hand and 16 ± 7 mm for arm muscle representation areas. In all patients the representation areas defined with nTMS and ECS were located on the same gyrus, also in patients with abundant interictal epileptic activity on the motor gyrus.
Conclusions: nTMS can reliably locate the hand motor cortical representation area with the accuracy needed for pre-surgical evaluation in patients with epilepsy.
Publication: Acta Neurochir (Wien). 2013 Mar;155(3):507-18. doi: 10.1007/s00701-012-1609-5. http://www.ncbi.nlm.nih.gov/pubmed/23328919
Introduction: Navigated transcranial magnetic stimulation (nTMS) is a non-invasive method to localize the primary motor cortex (M1).
Objective/Hypothesis: To assess the safety and feasibility of nTMS as a non-invasive preoperative mode of functional localization of M1 in epilepsy surgery candidates with intractable focal epilepsy due to lesions in the vicinity of M1.
Methods: We mapped the muscle representation areas of M1 with nTMS in 10 patients (age 2 to 55 years) with intractable epilepsy. The lesions were focal cortical dysplasia (n=6), ganglioglioma (n=2) polymicrogyria (n=1) or dysembryoblastic neuroepithelial tumor (n=1). The optimal stimulation sites and motor threshold (MT) of the distal hand or leg muscles were determined in both hemispheres. Cortical areas were mapped with stimulation intensities 100-120% of the MT to localize functional M1. Patients were on their stabile antiepileptic medication, and EEG was continuously monitored. The clinical benefit obtained with the preoperative nTMS mapping in the surgical decision making was scored as (1) essential, (2) beneficial, or (3) not beneficial, depending mainly on the difference between the functional and the presumed anatomic M1.
Results: The M1 was successfully assessed in all but the 2 youngest patients (aged 2 and 5 years), in whom nTMS was unable to elicit motor responses. nTMS was regarded as essential or beneficial in the localization of M1 in relation to the lesions in 6 out of 10 cases. The optimal motor representation areas were mainly located symmetrically on the precentral gyrus, and corresponded to the presumed location of M1 in MRI. No clinical or EEG evidence of acute epileptogenic adverse effects were observed during the localization procedure. None of the operated patients developed post-operative motor deficits.
Conclusions: nTMS is a safe and feasible clinical tool for the non-invasive preoperative localization of motor cortex in patients with intractable epilepsy due to focal lesions adjacent or within the presumed M1 in MRI.
Publication: Epilepsy Res. 2010 Dec;92(2-3):134-44. doi: 10.1016/j.eplepsyres.2010.08.013. http://www.ncbi.nlm.nih.gov/pubmed/20863666
Abstract: Invasive cortical mapping is conventionally required for preoperative identification of epileptogenic and eloquent cortical regions before epilepsy surgery. The decision on the extent and exact location of the resection is always demanding and multimodal approach is desired for added certainty. The present study describes two non-invasive preoperative protocols, used in addition to the normal preoperative work-up for localization of the epileptogenic and sensorimotor cortical regions, in two young patients with epilepsy. Magnetoencephalography (MEG) was used to determine the primary somatosensory cortex (S1) and the ictal onset zones. Navigated transcranial magnetic stimulation (nTMS) was used to determine the location and the extent of the primary motor representation areas. The localization results from these non-invasive methods were used for guiding the subdural grid deployment and later compared with the results from electrical cortical stimulation (ECS) via subdural grids, and validated by surgery outcome. The results from MEG and nTMS localizations were consistent with the ECS results and provided improved spatial precision. Consistent results of our study suggest that these non-invasive methods can be added to the standard preoperative work-up and may even hold a potential to replace the ECS in a subgroup of patients with epilepsy who have the suspected epileptogenic zone near the sensorimotor cortex and seizures frequent enough for ictal MEG.
Publication: Neuroimage. 2009 Apr 1;45(2):342-8. doi: 10.1016/j.neuroimage.2008.12.026. http://www.ncbi.nlm.nih.gov/pubmed/19159694
Purpose: The quality of presurgical evaluation in focal extratemporal epilepsy surgery is highly dependent on precise structural and functional identification of the epileptic focus. Navigated transcranial magnetic stimulation (nTMS) is a tool that combines the spatial information of high-resolution magnetic resonance imaging (MRI) with the functionality of non-invasive cortical stimulation. The non-invasive character of nTMS suggests that it could be a promising tool for presurgical evaluation of cortical excitability.
Methods: Presurgical nTMS evaluation was performed on an 8-year-old boy with left-sided intractable focal epilepsy, somatosensory auras and epilepsia partialis continua. In line with standardized procedures, motor evoked potentials were sought in both hemispheres over perirolandic cortex during simultaneous belly-tendon surface recordings of the first dorsal interosseus muscles.
Results: One singular motor-evoked potential (MEP) could be elicited in the unaffected hemisphere. In contrast, in the affected hemisphere MEPs could be elicited over a large area of the cortex even after the stimulation strength was reduced by at least 44%. Latency stratification in the affected hemisphere differentiated a motor from a sensory region of interest. Stimulation over the sensory region induced a sensory aura. The sensory site was concordant with a previous transient diffusion restriction found in an MRI two years prior to nTMS.
Conclusions: nTMS can locate pathological excitability with high spatial precision. Future studies should compare nTMS with direct cortex stimulation, as well as the combination of nTMS with electroencephalography (EEG) in a larger patient-collective.
Publication: Restorative Neurology and Neuroscience 28 (2010) 379–385.
Background: Recently, navigated transcranial magnetic stimulation (nTMS) has been suggested to be useful in preoperative functional localization of motor cortex in patients having tumors close to the somatomotor cortex. Resection of tumors in anatomically predicted eloquent areas without adverse effects have emphasized functional plasticity elicited by intracranial pathology.
Objective: To describe functional plasticity of motor cortex indicated by nTMS in two patients with epilepsy.
Methods: nTMS, functional MRI (fMRI), diffusion-tensor (DT)-tractography and magnetoencephalography (MEG) were utilized to preoperatively localize motor cortical areas in the workup for epilepsy surgery. The localizations were compared with each other, with the cortical anatomical landmarks, and in one patient with invasive electrical cortical stimulation (ECS).
Results: In two out of 19 studied patients, nTMS identified motor cortical sites that differed from those indicated by anatomical landmarks. In one patient, nTMS activated preferentially premotor cortex rather than pathways originating from the precentral gyrus. MEG and fMRI localizations conformed with nTMS whereas ECS localized finger motor function into the precentral gyrus. Resection of the area producing motor responses in biphasic nTMS did not produce a motor deficit. In the other patient, nTMS indicated abnormal ipsilateral hand motor cortex localization and confirmed the functionality of aberrant motor cortical representations of the left foot also indicated by fMRI and DT-tractography.
Conclusion: nTMS may reveal the functional plasticity and shifts of motor cortical function. Epileptic foci may modify cortical inhibition and the nTMS results. Therefore, in some patients with epilepsy, the nTMS results need to be interpreted with caution with regard to surgical planning.
Publication: Brain Stimul. 2013 May;6(3):286-91. doi: 10.1016/j.brs.2012.04.012. Epub 2012 May 23.
The Nexstim NBS System is indicated for noninvasive mapping of the primary motor cortex of the brain to its cortical gyrus. The NBS System provides information that may be used in the assessment of the primary motor cortex for pre-procedural planning.
Nexstim NexSpeech®, when used together with the NBS System, is indicated for noninvasive localization of cortical areas that do not contain essential speech function. NexSpeech® provides information that may be used in pre-surgical planning in patients undergoing brain surgery. Intraoperatively, the localization information provided by NexSpeech® is intended to be verified by direct cortical stimulation.
The Nexstim NBS System and NBS System with NexSpeech® are not intended to be used during a surgical procedure. The NBS System and NBS System with NexSpeech are intended to be used by trained clinical professionals.
1 Preoperative multimodal motor mapping: a comparison of magnetoencephalography imaging,navigated transcranial magnetic stimulation, and direct cortical stimulation By: Phiroz E. Tarapore, M.D., Mitchel S. Berger, M.D., et. al Journal of Neurosurgery. 2012 Aug;117(2):354-62. doi: 10.3171/2012.5.JNS112124
2 Preoperative motor mapping by navigated transcranial magnetic brain stimulation improves outcome for motor eloquent lesions By: Krieg SM, Ringel F, el. al Neuro-Oncology. 2014 Feb 9.