title: Continuous dynamic mapping of the corticospinal tract during surgery of motor eloquent brain tumors: evaluation of a new method.
abstract: OBJECTIVE
  The authors developed a new mapping technique to overcome the temporal and spatial limitations of classic subcortical mapping of the corticospinal tract (CST). The feasibility and safety of continuous (0.4-2 Hz) and dynamic (at the site of and synchronized with tissue resection) subcortical motor mapping was evaluated.
  
  
  METHODS
  The authors prospectively studied 69 patients who underwent tumor surgery adjacent to the CST (< 1 cm using diffusion tensor imaging and fiber tracking) with simultaneous subcortical monopolar motor mapping (short train, interstimulus interval 4 msec, pulse duration 500 μsec) and a new acoustic motor evoked potential alarm. Continuous (temporal coverage) and dynamic (spatial coverage) mapping was technically realized by integrating the mapping probe at the tip of a new suction device, with the concept that this device will be in contact with the tissue where the resection is performed. Motor function was assessed 1 day after surgery, at discharge, and at 3 months.
  
  
  RESULTS
  All procedures were technically successful. There was a 1:1 correlation of motor thresholds for stimulation sites simultaneously mapped with the new suction mapping device and the classic fingerstick probe (24 patients, 74 stimulation points; r(2) = 0.98, p < 0.001). The lowest individual motor thresholds were as follows: > 20 mA, 7 patients; 11-20 mA, 13 patients; 6-10 mA, 8 patients; 4-5 mA, 17 patients; and 1-3 mA, 24 patients. At 3 months, 2 patients (3%) had a persistent postoperative motor deficit, both of which were caused by a vascular injury. No patient had a permanent motor deficit caused by a mechanical injury of the CST.
  
  
  CONCLUSIONS
  Continuous dynamic mapping was found to be a feasible and ergonomic technique for localizing the exact site of the CST and distance to the motor fibers. The acoustic feedback and the ability to stimulate the tissue continuously and exactly at the site of tissue removal improves the accuracy of mapping, especially at low (< 5 mA) stimulation intensities. This new technique may increase the safety of motor eloquent tumor surgery.
authors.affiliation: Department of Neurosurgery, Inselspital, Bern University Hospital, Bern, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Raabe
authors.forename: Jürgen
authors.initials: J
authors.lastname: Beck
authors.forename: Philippe
authors.initials: P
authors.lastname: Schucht
authors.forename: Kathleen
authors.initials: K
authors.lastname: Seidel
mesh_terms: D000328:Adult; D000368:Aged; D001931:Brain Mapping; D001932:Brain Neoplasms / Q000503:physiopathology / Q000601:surgery*; D056324:Diffusion Tensor Imaging; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009044:Motor Cortex / Q000503:physiopathology / Q000601:surgery*; D019635:Neurosurgical Procedures / Q000379:methods*; D011712:Pyramidal Tracts / Q000503:physiopathology*