title: Navigated transcranial magnetic stimulation for "somatotopic" tractography of the corticospinal tract.
abstract: BACKGROUND
  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 (305.1±231.7 vs 1024±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±8.8% vs 58.3±16.6%, P<.001). Direct subcortical stimulation confirmed the CST location and the somatotopic reconstruction in all cases.
  
  
  CONCLUSIONS
  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.
authors: *Neurosurgical Clinic, Department of Neuroscience, and ‡Department of Radiological Sciences and Anatomy, University of Messina, Messina, Italy.
authors: Alfredo
authors: A
authors: Conti
authors: Giovanni
authors: G
authors: Raffa
authors: Francesca
authors: F
authors: Granata
authors: Vincenzo
authors: V
authors: Rizzo
authors: Antonino
authors: A
authors: Germanò
authors: Francesco
authors: F
authors: Tomasello
mesh_terms: D000328:Adult; D000368:Aged; D001931:Brain Mapping / Q000379:methods*; D001932:Brain Neoplasms / Q000473:pathology / Q000601:surgery*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D038361:Neuronavigation; D011446:Prospective Studies; D011712:Pyramidal Tracts / Q000473:pathology*; D015203:Reproducibility of Results; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult