NBS for pre-procedural planning

A new paradigm in functional mapping

At Nexstim we are using our decades of scientific research to help neurosurgeons and patients make informed decisions prior to treatment. As the world’s leading company combining TMS with 3D brain imaging, we offer tools for the noninvasive mapping of the vital eloquent cortices involved in motor and speech functions.

Plan neurosurgery with confidence

Assessing the anatomical location of the tumor can usually be based solely on MRI (with or without contrast). The locations of the vital functional areas may not always be the same as in a healthy person. As a tumor grows, it displaces grey matter, and the buildup of liquid can obscure the MRI. Due to brain plasticity, functions can also change location as a consequence of tumor growth.

In some patients, their cortex can re-organize important functions into adjacent tissues which would not normally be anatomically associated with function.

In challenging brain tumor, or epilepsy, a treatment plan is developed by the neurosurgical team, together with the patient. Once the type and grade of the tumor are understood, the most crucial information needed for a treatment decision are the anatomical location of the tumor and its location in relation to the brain's vital functions and their connections.

After craniotomy, neurosurgeons can rely on information from direct cortical stimulation. However, NBS (Navigated Brain Stimulation) can offer this same information with comparable accuracy, prior to surgery—in fact prior to any treatment decision. And, unlike other noninvasive functional mapping methods, NBS establishes a clear causal link between brain activation and function.

NBS is used after a patient has had a diagnosis of brain tumor, or other disorder, and when the lesion is thought to be close to vital areas of the brain, such as those responsible for limb movement or speech production. Brain maps from NBS are useful when deciding the treatment option. If neurosurgery is recommended, the mapping results help the surgeon plan the operation. Knowing the locations of vital brain functions prior to surgery helps lower the risk of any motor deficit post-operatively, thus helping preserve quality of life.

Importantly, the NBS motor map is an accurate and reliable picture which allows the patient and the doctor to discuss the best treatment option in this individual case. With clear and reliable information, the risks related to gross resection or debulking can be easier for the patient and their families to comprehend.

Requiring no active participation by the patient, NBS mapping is suitable for children, as well as for people with special needs, and can be successful even when the patient has hemiplegia.

Mapping the motor cortex with NBS

After an initial set-up process which aligns the patient head to a 3D rendering of the patient’s MRI head scan, NBS is used to find the primary motor cortex and determine the patient’s resting motor threshold (RMT) from the hand muscle representation area in the right hemisphere. Stimulation intensity is nominally set to 110% of RMT.

EMG (electromyography) surface electrodes are placed on the skin over the muscles of interest. These muscles may include the foot, leg and facial muscles, as well as those for the hand, arm and shoulder. The muscles will be chosen based on the lesion's location. The electrodes are normal surface electrodes which use gel or paste.

Moving and activating the coil, the operator will first find the area in the brain vital for controlling the thumb muscle. Next, the operator will determines how weak the stimulation intensity can be while still causing the thumb muscle to be activated, as can be seen from the EMG tracing displayed on the system screen. Knowing this intensity, the motor threshold, allows the operator to personalize the mapping to be both reliable and comfortable for the patient.

The operator will continue to activate the coil, moving it gradually over the head. Normally, only the areas around a tumor are mapped, so the tumor location determines which additional muscles will be monitored (usually the hand, arm and leg muscles on one side).

A session typically takes 15-30 minutes. It is important that the patient's muscles are relaxed during the whole session, and they relieve any muscle tension. Neuronavigation of the coil and the head allows the patient to move around in the chair.

After the mapping session

Normally, the patient's physician will review the results of the NBS mapping with the patient. Responses to stimuli will be shown as colored markers in a 3D model of the brain. Taking into account other diagnostic information, the physician will discuss treatment options. NBS results can be of significant help when discussing possible trade-offs between treatment risks and expected benefits.

Validation of NBS mapping in clinical practise

Multiple clinical studies have proven that Navigated Brain Stimulation, as an adjunct to direct cortical stimulation, results in a 35% increase or greater, in the rate of gross total resection.1,2

In a recent study of 250 consecutive patients, presurgical mapping with Navigated Brain Stimulation enabled a more aggressive surgical strategy in more the 75% of the cases. The same study using navigated TMS (nTMS) disproved suspected involvement of primary motor cortex in over 25% of the cases, expanding surgical indication by 14.8%. Concluding that the integration of nTMS into the surgical workflow crucially improves pre-operative planning, patient counseling, and surgical procedures. Leading to longer progression-free survival rates and better neurological outcomes by expanding the indications and extent of resection.2 

1 Preoperative motor mapping by navigated transcranial magnetic brain stimulation improves outcome for motor eloquent lesions Krieg SM, Ringel F et al. Neuro-Oncology. 2014 Feb 9.

2 Navigated transcranial magnetic stimulation improves the treatment outcome in patients with brain tumors in motor eloquent locations By: Frey D, P Vajkoczy et. al. Neuro-Oncology. 2014 Jun 12

Mapping language-eloquent cortex

Navigated Transcranial Magnetic Stimulation in Neurosurgery

nTMS makes surgery safer, the resection rates are higher and—in the end—the outcomes are better.

Bernhard Meyer, MD, Professor & Chair,
Department of Neurosurgery, Klinikum rechts der Isar, Technical University of Munich, Germany.

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What makes this so special is the ability for it to define very small, precise cortical regions on the surface of the brain, and define individual components of function which is something we never could do before.

Mitchel Berger, M.D. Chairman of the Department of Neurological Surgery, Director of the Brain Tumor Surgery Program, University of San Francisco, USA.

Navigated Brain Stimulation is a standard of care in our department. Moreover, since we were able to show that the presurgical mappings increase the extent of resection and reduce surgery-related paresis, the NBS data is also used for decision making in our neurosurgical tumor board and for outpatient consultation.

Sandro M. Krieg, M.D. Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.

Indications for use

The Nexstim Navigated Brain Stimulation (NBS) System 5 is indicated for non-invasive mapping of the primary motor cortex of the brain to its cortical gyrus. The Nexstim NBS System 5 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 5, is indicated for non-invasive 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. Intra-operatively, the localization information provided by NexSpeech® is intended to be verified by direct cortical stimulation.

The Nexstim NBS System 5 and NBS System 5 with NexSpeech® are not intended to be used during a surgical procedure.

The Nexstim NBS System 5 and NBS System 5 with NexSpeech® are intended to be used by trained clinical professionals.