title: Low-threshold monopolar motor mapping for resection of lesions in motor eloquent areas in children and adolescents.
abstract: OBJECTIVE
  Resection of lesions close to the primary motor cortex (M1) and the corticospinal tract (CST) is generally regarded as high-risk surgery due to reported rates of postoperative severe deficits of up to 50%. The authors' objective was to determine the feasibility and safety of low-threshold motor mapping and its efficacy for increasing the extent of lesion resection in the proximity of M1 and the CST in children and adolescents.
  
  
  METHODS
  The authors analyzed 8 consecutive pediatric patients in whom they performed 9 resections for lesions within or close (≤ 10 mm) to M1 and/or the CST. Monopolar high-frequency motor mapping with train-of-five stimuli (pulse duration 500 μsec, interstimulus interval 4.0 msec, frequency 250 Hz) was used. The motor threshold was defined as the minimal stimulation intensity that elicited motor evoked potentials (MEPs) from target muscles (amplitude > 30 μV). Resection was performed toward M1 and the CST at sites negative to 1- to 3-mA high-frequency train-of-five stimulation.
  
  
  RESULTS
  The M1 was identified through high-frequency train-of-five via application of varying low intensities. The lowest motor thresholds after final resection ranged from 1 to 9 mA in 8 cases and up to 18 mA in 1 case, indicating proximity to motor neurons. Intraoperative electroencephalography documented an absence of seizures during all surgeries. Two transient neurological deficits were observed, but there were no permanent deficits. Postoperative imaging revealed complete resection in 8 patients and a very small remnant (< 0.175 cm3) in 1 patient.
  
  
  CONCLUSIONS
  High-frequency train-of-five with a minimal threshold of 1-3 mA is a feasible and safe procedure for resections in the proximity of the CST. Thus, low-threshold motor mapping might help to expand the area for safe resection in pediatric patients with lesions located within the precentral gyrus and close to the CST, and may be regarded as a functional navigational tool. The additional use of continuous MEP monitoring serves as a safety feedback for the functional integrity of the CST, especially because the true excitability threshold in children is unknown.
authors.affiliation: Departments of Neurosurgery.
authors.forename: Philippe
authors.initials: P
authors.lastname: Schucht
authors.forename: Kathleen
authors.initials: K
authors.lastname: Seidel
authors.forename: Michael
authors.initials: M
authors.lastname: Murek
authors.forename: Lennart Henning
authors.initials: LH
authors.lastname: Stieglitz
authors.forename: Natalie
authors.initials: N
authors.lastname: Urwyler
authors.forename: Roland
authors.initials: R
authors.lastname: Wiest
authors.forename: Maja
authors.initials: M
authors.lastname: Steinlin
authors.forename: Kurt
authors.initials: K
authors.lastname: Leibundgut
authors.forename: Andreas
authors.initials: A
authors.lastname: Raabe
authors.forename: Jürgen
authors.initials: J
authors.lastname: Beck
mesh_terms: D000293:Adolescent; D001931:Brain Mapping / Q000379:methods*; D001932:Brain Neoplasms / Q000503:physiopathology / Q000601:surgery*; D002648:Child; D002675:Child, Preschool; D004569:Electroencephalography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D016343:Monitoring, Intraoperative / Q000379:methods*; D009044:Motor Cortex / Q000503:physiopathology*; D012640:Seizures / Q000503:physiopathology