Tag: Navigated brain stimulation

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Mapping of cortical language function by functional magnetic resonance imaging and repetitive navigated transcranialmagnetic stimulation in 40 healthy subjects

Mapping of cortical language function by functional magnetic resonance imaging and repetitive navigated transcranial magnetic stimulation in 40 healthy subjects

Acta Neurochir (2016) 158:1303–1316

Functional magnetic resonance imaging (fMRI) is considered to be the standard method regarding noninvasive language mapping. However, repetitive navigated transcranial magnetic stimulation (rTMS) gains increasing importance with respect to that purpose. However, comparisons between both methods are sparse.

Methods We performed fMRI and rTMS language mapping of the left hemisphere in 40 healthy, right-handed subjects in combination with the tasks that are most commonly used in the neurosurgical context (fMRI: word-generation=WGEN task; rTMS: object-naming=ON task). Different rTMS error rate thresholds (ERTs) were calculated, and Cohen’s kappa coefficient and the cortical parcellation system (CPS) were used for systematic comparison of the two techniques.

Results Overall, mean kappa coefficients were low, revealing no distinct agreement. We found the highest agreement for both techniques when using the 2-out-of-3 rule (CPS region defined as language positive in terms of rTMS if at least 2 out of 3 stimulations led to a naming error). However, kappa for this threshold was only 0.24 (kappa of <0, 0.01–0.20, 0.21– 0.40, 0.41–0.60, 0.61–0.80 and 0.81–0.99 indicate less than chance, slight, fair, moderate, substantial and almost perfect agreement, respectively).

Conclusions Because of the inherent differences in the underlying physiology of fMRI and rTMS, the different tasks used and the impossibility of verifying the results via direct cortical stimulation (DCS) in the population of healthy volunteers, one must exercise caution in drawing conclusions about the relative usefulness of each technique for language mapping. Nevertheless, this study yields valuable insights into these two mapping techniques for the most common language tasks currently used in neurosurgical practice.

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Navigated Transcranial Magnetic Stimulation for “Somatotopic” Tractography of the Corticospinal Tract

SOMATOTOPIC RECONSTRUCTION OF CORTICOSPINAL TRACT

Operative Neurosurgery 10:542–554, 2014

Diffusion tensor imaging tractography provides 3-dimensional reconstruction of principal white matter tracts, but its spatial accuracy has been questioned. Navigated transcranial magnetic stimulation (nTMS) enables somatotopic mapping of the motor cortex.

OBJECTIVE: We used motor maps to reconstruct the corticospinal tract (CST) by integrating elements of its somatotopic organization. We analyzed the accuracy of this method compared with a standard technique and verified its reliability with intraoperative subcortical stimulation.

METHODS: We prospectively collected data from patients who underwent surgery between January 2012 and October 2013 for lesions involving the CST. nTMS-based diffusion tensor imaging tractography was compared with a standard technique. The reliability and accuracy between the 2 techniques were analyzed by comparing the number of fibers, the concordance in size, and the location of the cortical end of the CST and the motor area. The accuracy of the technique was assessed by using direct subcortical stimulation.

RESULTS: Twenty patients were enrolled in the study. nTMS-based tractography provided a detailed somatotopic reconstruction of the CST. This nTMS-based reconstruction resulted in a decreased number of fibers (305.16 231.7 vs 10246 193, P , .001) and a significantly greater overlap between the motor cortex and the cortical end-region of the CST compared with the standard technique (90.5 6 8.8% vs 58.3 6 16.6%, P , .001). Direct subcortical stimulation confirmed the CST location and the somatotopic reconstruction in all cases.

CONCLUSION: These results suggest that nTMS-based tractography of the CST is more accurate and less operator dependent than the standard technique and provides a reliable anatomic and functional characterization of the motor pathway.

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Navigated transcranial magnetic stimulation for mapping the motor cortex in patients with rolandic brain tumors

Navigated transcranial

Neurosurg Focus 34 (4):E3, 2013

Navigated transcranial magnetic stimulation (nTMS) is a novel technology in the field of neurosurgery for noninvasive delineation of cortical functional topography. This study addresses the spatial accuracy and clinical usefulness of nTMS in brain tumor surgery in or near the motor cortex based on a systematic review of observational studies.

Methods. A systematic search retrieved 11 reports published up to October 2012 in which adult patients were examined with nTMS prior to surgery. Quality criteria consisted of documentation of the influence of nTMS brain mapping on clinical decision making in a standardized prospective manner and/or performance of intraoperative direct electrical stimulation (DES) and comparison with nTMS results. Cross-observational assessment of nTMS accuracy was established by calculating a weighted mean distance between nTMS and DES.

Results. All studies reviewed in this article concluded that nTMS correlated well with the “gold standard” of DES. The mean distance between motor cortex identified on nTMS and DES by using the mean distance in 81 patients described in 6 quantitatively evaluated studies was 6.18 mm. The nTMS results changed the surgical strategy based on anatomical imaging alone in 25.3% of all patients, based on the data obtained in 87 patients in 2 studies.

Conclusions. The nTMS technique spatially correlates well with the gold standard of DES. Its functional information benefits surgical decision making and changes the treatment strategy in one-fourth of cases.

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Diffusion tensor imaging fiber tracking using navigated brain stimulation

Acta Neurochir (2012) 154:555–563. DOI 10.1007/s00701-011-1255-3

Navigated brain stimulation (NBS) is a newly evolving technique. In addition to its supposed purpose, e.g., preoperative mapping of the central region, little is known about its further use in neurosurgery. We evaluated the usefulness of diffusion tensor imaging fiber tracking (DTI-FT) based on NBS compared to conventional characterization of the seed region.

Methods We examined 30 patients with tumors in or close to the corticospinal tract (CST) using NBS with the Nexstim eXimia system. NBS was performed for motor cortex mapping, and DTI-FT was performed by three different clinicians using BrainLAB iPlan® Cranial 3.0.1 at two time points. Number of fibers, tract volume, aberrant tracts, and proximity to the tumor were compared between the two methods.

Results We recognized a higher number of fibers (1,298± 1,279 vs. 916±986 fibers; p<0.01), tract volume (23.0±15.3 vs. 18.3±14.0 cm3; p<0.01), and aberrant tracts (0.6±0.5 vs. 0.3±0.5 aberrant tracts/tracked CST; p<0.001) when the seed region was defined conventionally, while proximity of the tracts to the tumor did not differ. While NBS-based DTI-FT is independent of the planning clinician, conventional outlining of the seed region shows generally higher variability between investigators.

Conclusions Conventional DTI-FT showed significant differences between the two modalities, most likely because of the more specific definition of the seed region when DTI-FT is based on NBS. Moreover, NBS-aided DTI fiber tracking is user-independent and, therefore, a method for further standardization of DTI fiber tracking.

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