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NBS facilitates early resection of low-grade gliomas in the motor cortex

16 September 2013

HELSINKI, Finland—Sept. 16, 2013--Low-grade gliomas LGG in the primary motor cortex present neurosurgeons with a dilemma: resection risks causing post-operative deficits whereas observation alone may entail early neurological symptoms and lower life expectancy for the patient. Although it is widely recognized today that LGGs should be surgically resected, 50 % of neurosurgeons do not operate on non-enhancing gliomas in general, and the rate is likely to be even lower when the tumor occurs in the primary motor cortex.

In their recently published paper The preoperative use of navigated transcranial magnetic stimulation facilitates early resection of suspected low-grade gliomas in the motor cortex, clinicians at the Department of Neurosurgery, Charité University Hospital, Berlin designed a study that shows the impact the availability of navigated TMS (nTMS) mapping presurgically can have on neurosurgical decision-making compared to a time when reliable presurgical planning data was not available.

The nTMS group comprised the first 11 patients with gliomas in the primary motor cortex that were non-enhancing on MRI, since the adoption of routine nTMS mapping using the Nexstim NBS System at the Charité. The comparison group consisted of the 11 patients with similar diagnoses immediately prior to the availability of the NBS System.

Using the NBS System, nTMS mapping was successful in delineating functional versus non-functional motor cortex tissue in all 11 patients, also within the area of altered FLAIR signal on MRI. In 6 out of these 11 patients, the nTMS mapping result changed the surgical plan towards early and more extensive resection. After the availability of nTMS mapping, all 11 LGG patients had surgical resection. Prior to the availability of NBS, only 3 out of 11patients had a surgical resection - the remainder typically received only radiotherapy or chemotherapy.

From baseline to 1-year post-surgical assessment by MRI, there was a highly significant (p < 0.001) median change of tumor volume from +12 % in the comparison group to -83 % in the nTMS group. In the nTMS-mapped patients, 1 out of 4 patients with pre-operative neurological deficits had an improved status at one year; whereas the historical comparison group had increased neurological deficits at one year in 3 out of the 8 patients not offered surgical treatment. 

The authors concluded that, "nTMS provides accurate motor mapping results also in infiltrative gliomas and enables more frequent and more extensive surgical resection of non-enhancing gliomas in or near the primary motor cortex. The substantial differences observed here in neurological and oncological outcomes suggest that further comparative research is warranted."

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