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navigated_transcranial_magnetic_stimulation

Navigated transcranial magnetic stimulation (nTMS) is a technology for noninvasive delineation of cortical functional topography.

Indications

Preoperative nTMS results correlate well with direct cortical stimulation (DCS) data in the identification of the primary motor cortex. Repetitive nTMS can also be used for mapping of speech-sensitive cortical areas.

see Navigated transcranial magnetic stimulation for language mapping.

It has become established as an accurate noninvasive technique for mapping the functional motor cortex for the representation areas of upper and lower limb muscles, facial muscles in the lower part of the face. Instead of using the motor threshold (MT) of the abductor pollicis brevis, the stimulus intensity during mapping should be proportioned to the MT of a facial muscle 1).

Its functional information benefits surgical decision making and changes the treatment strategy in one-fourth of cases 2).

Magnetic resonance images are being increasingly deployed in conjunction with navigated transcranial magnetic stimulation (nTMS) to account for inter-individual differences in brain anatomy as well as to reduce the variability of mapping findings.

Navigated transcranial magnetic stimulation (nTMS) has been recently established as a reliable tool for distinguishing resectable from nonresectable cortical tissue in the motor areas 3) 4).

Within the primary motor cortex, navigated transcranial magnetic stimulation (nTMS) has been shown to yield maps strongly correlated with those generated by direct cortical stimulation (DCS).

Provides crucial data for preoperative planning and surgical resection of tumors involving essential motor areas. Expanding surgical indications and extent of resection based on nTMS enables more patients to undergo surgery and might lead to better neurological outcomes and higher survival rates in brain tumor patients 5).

Tractography implementation

The implementation of tractography based on nTMS increases the accuracy of fiber tracking. Moreover, this combination of methods has the potential to become a supplemental tool for guiding electrode implantation 6).

Case series

2016

113 patients undergoing bihemispheric nTMS examination prior to surgery for gliomas in presumed motor eloquent locations. Multiple ordinal logistic regression analysis was performed to test for any association between preoperative nTMS-related variables and postoperative motor outcome.

A new motor deficit or deterioration due to a preexisting deficit was observed in 20% of cases after 7 days and in 22% after 3 months. In terms of tumor location, no new permanent deficit was observed when the distance between tumor and corticospinal tract was greater than 8 mm and the precentral gyrus was not infiltrated (p = 0.014). New postoperative deficits on Day 7 were associated with a pathological excitability of the motor cortices (interhemispheric resting motor threshold [RMT] ratio < 90% or > 110%, p = 0.031). Interestingly, motor function never improved when the RMT was significantly higher in the tumorous hemisphere than in the healthy hemisphere (RMT ratio > 110%).

The proposed risk stratification model, based on objective functional-anatomical and neurophysiological measures, enables one to counsel patients about the risk of functional deterioration or the potential for recovery 7).


Between 2010 and 2013, nTMS motor mapping was performed in a prospective cohort of 100 patients with brain tumors in or adjacent to the rolandic cortex. Spatial data analysis was performed by normalization of the individual motor maps and creation of overlays according to tumor location. Analysis of motor evoked potential (MEP) latencies was performed regarding mean overall latencies and potentially polysynaptic latencies, defined as latencies longer than 1 SD above the mean value. Hemispheric dominance, lesion location, and motor-function deficits were also considered.

Graphical analysis showed that motor areas were not restricted to the precentral gyrus. Instead, they spread widely in the anterior-posterior direction. An analysis of MEP latency showed that mean MEP latencies were shortest in the precentral gyrus and longest in the superior and middle frontal gyri. The percentage of latencies longer than 1 SD differed widely across gyri. The dominant hemisphere showed a greater number of longer latencies than the nondominant hemisphere (p < 0.0001). Moreover, tumor location-dependent changes in distribution of polysynaptic latencies were observed (p = 0.0002). Motor-function deficit did not show any statistically significant effect.

The distribution of primary and polysynaptic motor areas changes in patients with brain tumors and highly depends on tumor location. Thus, these data should be considered for resection planning 8).

1)
Säisänen L, Julkunen P, Kemppainen S, Danner N, Immonen A, Mervaala E, Määttä S, Muraja-Murro A, Könönen M. Locating and Outlining the Cortical Motor Representation Areas of Facial Muscles With Navigated Transcranial Magnetic Stimulation. Neurosurgery. 2015 Sep;77(3):394-405. doi: 10.1227/NEU.0000000000000798. PubMed PMID: 26035404.
2)
Takahashi S, Vajkoczy P, Picht T. Navigated transcranial magnetic stimulation for mapping the motor cortex in patients with rolandic brain tumors. Neurosurg Focus. 2013 Apr;34(4):E3. doi: 10.3171/2013.1.FOCUS133. Review. PubMed PMID: 23544409.
3)
Picht P, Schmidt S, Brandt S, et al. Preoperative functional mapping for rolandic brain tumor surgery: comparison of navigated transcranial magnetic stimulation to direct cortical stimulation. Neurosurgery 2011;69(3):581-589.
4)
Tarapore PE, Tate MC, Findlay AM, et al. Preoperative multimodal motor mapping: a comparison of magnetoencephalography imaging, navigated transcranial magnetic stimulation, and direct cortical stimulation. J Neurosurg 2012;117(2):354-362.
5)
Frey D, Schilt S, Strack V, Zdunczyk A, Rösler J, Niraula B, Vajkoczy P, Picht T. Navigated transcranial magnetic stimulation improves the treatment outcome in patients with brain tumors in motor eloquent locations. Neuro Oncol. 2014 Jun 12. pii: nou110. [Epub ahead of print] PubMed PMID: 24923875.
6)
Forster MT, Hoecker AC, Kang JS, Quick J, Seifert V, Hattingen E, Hilker R, Weise LM. Does Navigated Transcranial Stimulation Increase the Accuracy of Tractography? A Prospective Clinical Trial Based on Intraoperative Motor Evoked Potential Monitoring During Deep Brain Stimulation. Neurosurgery. 2015 Jun;76(6):766-776. PubMed PMID: 25988930.
7)
Rosenstock T, Grittner U, Acker G, Schwarzer V, Kulchytska N, Vajkoczy P, Picht T. Risk stratification in motor area-related glioma surgery based on navigated transcranial magnetic stimulation data. J Neurosurg. 2016 Jun 3:1-11. [Epub ahead of print] PubMed PMID: 27257834.
8)
Bulubas L, Sabih J, Wohlschlaeger A, Sollmann N, Hauck T, Ille S, Ringel F, Meyer B, Krieg SM. Motor areas of the frontal cortex in patients with motor eloquent brain lesions. J Neurosurg. 2016 Mar 11:1-12. [Epub ahead of print] PubMed PMID: 26967780.
navigated_transcranial_magnetic_stimulation.txt · Last modified: 2017/07/13 23:14 by administrador