Pre-op
motor
mapping
Applications: Brain tumour surgery, epilepsy surgery, cerebrovascular surgery, radiation therapy
Functionally map eloquent motor regions prior to surgery
It is well known that gross total resection improves overall survival and progression-free survival in glioma patients. For this reason, although advances in diagnostic imaging have enabled tumour margins to be more clearly defined, anatomic criteria alone are not always reliable in accurately localizing areas of motor function.
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Intraoperative brain mapping remains the gold standard for motor mapping; however, noninvasive preoperative methods are becoming increasingly accurate and useful to guide surgery, especially for pre-surgical planning. The anatomical and functional data provided by pre-surgical nTMS have shown a very good correlation with those provided by brain mapping performed intraoperatively, with a difference in the location of the motor hotspot that remains less than 15 mm between the two techniques, varying between 2 and 8 mm on average in several studies. This information can be used to plan the extent of resection, but also the least invasive trajectory to the tumour, thereby effectively reducing the associated risks of operating in eloquent areas.
Compared to fMRI, which is widely utilized for identifying the motor cortex, nTMS has better spatial and temporal resolution and provides an immediate result, without recourse to complex post-processing analysis. While fMRI relies on neurovascular coupling, nTMS establishes a clearer causal relationship between the stimulation point and observed response (e.g., MEP). While fMRI requires active participation of the individual since it is task- based, nTMS is more of a passive modality and presents fewer restrictions in clinical practice.
How?
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The hand knob is identified on the patient's MRI and the necessary depth and stimulation parameters are altered to ensure adequate activation.
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The stimulation intensity is adjusted to be suitable for mapping, with the MEP hand response captured and documented.
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Stimulation continues along the central sulcus toward the midline and the Sylvian fissure, with the E-field orientation perpendicular to the central sulcus.
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The coil is then tested in various orientations to ensure that the gyrus is being tested most effectively.
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Each positive site is 'marked' on the patient's MRI, which is then sent back to the consultant surgeon for analysis.
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After analysis, the En-TMS data can be exported for inclusion in the navigation system on the day of the procedure to be matched with direct cortical stimulation data.
Hospital purchase of Nexstim NBS
In-house:
Referral for patient MRI
Outsourced:
Patient books appointment with Neuroclast
En-TMS conducted by Neuroclast
Data sent to consultant surgeon for analysis
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EDB
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Lower extremity motor mapping in a consenting healthy participant at Neuroclast. With intensity at 55%, nTMS was able to discriminate between the tibialis anterior, abductor hallucis and extensor digitorum brevis, in addition to mapping the face, arm and hand.
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A: M1 stimulation with e-field navigation: positive hand motor evoked responses observed (left). B: S1 stimulation with e-field navigation: zero positive hand motor evoked responses observed (right; Nikolenk & Picht, 2017).
En-TMS conducted by Neuroclast may be included in multiple multi-centre trials throughout Australia. Consent will be sought prior to any data capture, and acquired from the patient, consultant and hospital.
Recommended Reading
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Chapter 5. Nikolenko, O. & Picht, T. (2017). Navigated TMS in Neurosurgery. 87-97.
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Haddad et al. (2021). Preoperative applications of navigated transcranial magnetic stimulation. Frontiers in Neurology, 11, 1-11.
For patients:
Surgical procedures of any description pose risk. This is a safe and non-invasive measure to distinguish how close or far the areas of the brain are with respect to your procedure. Just because you're here reading this does not mean that you're in immediate danger whatsoever, in fact, this is a proactive and preventative measure to ensure that all possible data is acquired to contribute to a safe procedure.
When you schedule an appointment with Neuroclast, you'll be greeted and given an overview of the technology and what's in store. Here's a brief summary to get you ahead:
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You'll enter our clinic, and see a big fancy piece of equipment
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You'll sit in a comfortable chair and engage in banter with our clinical specialists
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We'll load up your MRI scan, and find the 'target' areas necessary for mapping
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If it puts you at ease, we'll show you how it works first!
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You will hear occasional semi-loud clicks, and at times you may feel a twitch - all is perfectly normal
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The test takes between 25-40 minutes, and then you're good to go!
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We'll forward your data to your surgeon