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Pre-op
neurologic
risk
 

Applications: Brain tumour surgery involving the corticospinal system

Electrophysiologic insight regarding tumour infiltration

Analysis of neuro-imaging often yields meaningful insight as to the risk of a brain tumour relative to anatomy involving the functional areas of the brain.

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fMRI is an indirect measure of neurological function via the BOLD signal that reflects increased metabolism. However, tumour infiltration also affects brain metabolism and oxygenation levels, which ultimately can contribute to false positive and false negative BOLD activities.

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The distance from tumour margins and subcortical tracts can also be accurately calculated by nTMS-based DTI FT, referred to as the lesion-to-tract distance (LTD), where risk of iatrogenic injury is significantly lower when distance between tumour and tracts exceeded 12mm (CST),16mm (arcuate fasciculus) and 25mm (other close language related tracts). 

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nTMS mapping is able to supplement risk assessment of the upcoming surgery and predict the likelihood of postoperative neurological outcomes with objective quantitative output of the corticospinal system's functional status by comparing lesion and non-lesion hemispheres.

How?

  • Corticospinal excitability (CSE) refers to the efficacy in which the motor cortex can be activated after stimulation.

  • It takes into consideration the recruitment curve (RC), or how easily a response can be facilitated;

  • the cortical silent period (CSP), which reflects the excitability in cortical inhibitory circuits;

  • the resting motor threshold (rMT), which is the minimum required pulse stimulation intensity;

  • the interhemispheric rMT ratio, which considers the rMT of the tumour hemisphere, divided by the value of the unaffected hemisphere and represented as a percentage.

  • For brain tumour patients, an rMT ratio of more than 110% and less than 90% reflects the imbalance of facilitation and probable inhibition of M1 (+/- PMC/SMA).

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

risk1_1.png

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​Pre-op:

  • 72 y/o female, right temporal GBM IV

  • BMRC grade 5 (normal motor function)

  • Distance from tumour to CST > 8mm

  • rMT ratio 78% (< 90% = low)

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Post-op:

  • Extent of resection: subtotal resection, 2mm of residual contrast-enhancing tumour tissue

  • 7 days: BMRC grade 4, worsening left sided hemiparesis

risk1_2.png

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​Pre-op:

  • 41 y/o female, right temporal GBM IV

  • BMRC grade 5 (normal motor function)

  • Distance from tumour to CST > 8mm

  • rMT ratio 91% (90-110% = normal)

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Post-op:

  • Extent of resection: no residual contrast-enhancing tissue on T1-weighted images

  • 7 days: BMRC grade 5, no new motor deficit

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​

  • Rosenstock, T. et al. (2017). Risk stratification in motor area-related glioma surgery based on navigated transcranial magnetic stimulation data. J Neurosurg, 126(4), 1227-1237.

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:

  • You'll enter our clinic, and see a big fancy piece of equipment

  • You'll sit in a comfortable chair and engage in banter with our clinical specialists

  • We'll load up your MRI scan, and find the 'target' areas necessary for mapping

  • If it puts you at ease, we'll show you how it works first!

  • You will hear occasional semi-loud clicks, and at times you may feel a twitch - all is perfectly normal

  • The test takes between 25-40 minutes, and then you're good to go!

  • We'll forward your data to your surgeon

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