title: Neurophysiological monitoring for safe surgical tethered cord syndrome release in adults.
abstract: BACKGROUND
  Release of tethered spinal cord by sectioning of the filum terminale carries a significant risk of injury to the neighboring motor and sensory nerve roots. Intraoperative neurophysiological monitoring techniques can help to minimize these adverse neurologic outcomes.
  
  
  METHODS
  We performed a retrospective review of 67 consecutive patients undergoing tethered cord release. We excluded 52 pediatric patients which limited our study to 15 adult patients treated during a four year period, including patients with a thick filum, low lying conus, myelomeningocele, filum tumor, spinal cord malformation, and/or lipoma. Clinical outcomes were determined from postoperative follow-up visits. Two patients were lost to follow up and were excluded from the clinical outcome analysis. Electrical stimulation of the filum terminale and lumbo-sacral nerve roots in conjunction with electromyogram (EMG) recording was performed intraoperatively.
  
  
  RESULTS
  The mean electrical threshold for EMG response during stimulation of the filum terminale was 37.1 volts (V), range 15 to 100 V. In comparison, the lowest threshold obtained by direct stimulation of the ventral nerve roots was a mean of 1.46 V, with a range of 0.1 to 7 V. More than 70% of the patients studied demonstrated a filum to motor root threshold ratio of 100:1 or greater. No patient developed new neurologic symptoms or signs postoperatively. Bowel and bladder function improved in 46% of patients, back pain in 39% and motor function in 31%. Eight percent reported decline in bladder control and worsening back pain postoperatively.
  
  
  CONCLUSIONS
  The often dramatic difference in the threshold of the filum terminale and adjacent motor nerve roots (100:1) helps to identify, isolate, and safely section the filum terminale. Tethered cord release using intraoperative neurophysiological monitoring is safe and in the majority of cases leads to improvement or at least, stabilization of neurologic function. Monitoring prevented intraoperative nerve root injury that might have resulted in immediate onset of new neurologic deficits caused by the surgical procedure.
authors.affiliation: Department of Neurological Surgery, University of California-San Francisco, 505 Parnassus Avenue, Moffitt Hospital Room M779, Box 112, San Francisco, CA 94143-0112, USA.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Quiñones-Hinojosa
authors.forename: Chirag A
authors.initials: CA
authors.lastname: Gadkary
authors.forename: Mittul
authors.initials: M
authors.lastname: Gulati
authors.forename: Cornelia S
authors.initials: CS
authors.lastname: von Koch
authors.forename: Russ
authors.initials: R
authors.lastname: Lyon
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Weinstein
authors.forename: Charles D
authors.initials: CD
authors.lastname: Yingling
mesh_terms: D000328:Adult; D000368:Aged; D002420:Cauda Equina / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D004056:Differential Threshold; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D007431:Intraoperative Complications / Q000517:prevention & control; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D009420:Nervous System / Q000503:physiopathology*; D009436:Neural Tube Defects / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D012189:Retrospective Studies; D013116:Spinal Cord / Q000601:surgery*; D013126:Spinal Nerve Roots / Q000293:injuries / Q000503:physiopathology; D014950:Wounds, Penetrating / Q000517:prevention & control