Pre-op speech mapping

Applications: Brain tumour surgery, epilepsy surgery, cerebrovascular surgery, radiation therapy

Eliminate ambiguity with functional data

Language-related activations found by fMRI can be ambiguous in estimating the results of brain mapping in awake craniotomy, however navigated and repetitive (nrTMS) language mapping might be superior to fMRI in the vicinity of brain lesions as it is far less prone to artifact based on increased vascularity and altered tissue oxygenation.

There is a clear individual variability in the sites where nrTMS induces language disturbance, paralleling individuality seen in cortical mapping data during awake surgery, and this methodology also provides an accurate monitoring and high-fidelity report of behavioural nrTMS studies.

The main indications for preoperative nrTMS language mapping are tumours located in “classical” language areas, that is, the left perisylvian cortex, especially in the frontal operculum and temporoparietal region. Though evidence regarding relevant speech and language function outside of these areas, also in the non-dominant hemisphere, is increasing.

A high negative predictive value has been a consistent finding, indicating that nrTMS produces reliable “negative maps” sufficient to plan brain tumour and epilepsy surgery. 

How?

  • fMRI is obtained (where possible) with silent object naming, silent sentence generation, and simple motor tasks

  • If an fMRI is not available, an MRI is obtained.

  • nTMS localises the hand knob as a reference point and records the MEP

  • nrTMS is introduced with a new coil for repetitive stimulation

  • Object naming and sentence generation tasks are employed during nrTMS, to compare to fMRI data

  • For each stimulated site, responses are categorised: A, no response (speech arrest); B, hesitation; C, circumlocution; D, semantic paraphasia; E, phonological paraphasia; F, neologism; and G, normal response

  • All testing sites are marked and categorized

  • At the end of the nrTMS session, the recorded language-positive stimulation points (responses A–F) are verified for accuracy, converted to 5 mm spheres, and exported as regular DICOM images for further use. 

  • For comparison, seed points are generated anatomically, fMRI-based and rnTMS based, often beginning at the arcuate fascicle.

Hospital purchase of Nexstim NBS system with NexSpeech® 

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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Positive speech disturbance (performance error) after stimulation towards anterior supramarginal gyrus in consenting healthy participant during object naming at Neuroclast. The participant also describes what the sensational felt like.

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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

  • Chapter 8. Nikolenko, O. & Picht, T. (2017). Navigated TMS in Neurosurgery. 131-151.

  • 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:

  • 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

  • For this particular test, we're targeting the parts of your brain that enable you to talk. When we target these areas you may experience a momentary disruption of speech - again this is perfectly normal.

  • The test takes between 30-60 minutes, and then you're good to go!

  • We'll forward your data to your surgeon