Ahead of Print: Navigated Transcranial Magnetic Stimulation for “Somatotopic” Tractography

Screen Shot 2014-11-17 at 8.36.23 AMBackground: Diffusion tensor imaging (DTI) tractography provides three-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 to 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 DTI tractography was compared with a standard technique. The reliability and accuracy between the two 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 using direct subcortical stimulation (DSS).

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 (305.1 +/- 231.7 vs 1024 +/- 193, p<0.001) and a significantly greater overlap between the motor cortex and the cortical end-region of the CST compared to the standard technique (90.5 +/- 8.8% vs 58.3 +/- 16.6%, p < 0.0001). DSS 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 anatomical and functional characterization of the motor pathway.

From: Navigated Transcranial Magnetic Stimulation for “Somatotopic” Tractography of the Cortico-Spinal Tract by Conti et al.

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