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Neuromonitoring (also intraoperative neurological monitoring/IONM or surgical neurophysiology or simply intraoperative monitoring/IOM) is the practice of recording nerve signals and brainwaves during surgeries with the aim of 1) reduce the risk to the patient of iatrogenic damage to the nervous system, and/or 2) provide functional guidance to the surgeon. .

Surgical procedures that most often require neuromonitoring include but are not limited to the following: carotid endarterectomy, anterior cervical diskectomy, instrumentation for spinal instability including pedicle screws, scoliosis correction, spinal cord untethering, and treatment of cranial base tumors, posterior fossa, microvascular decompression, intracranial aneurysms and arteriovenous malformations.

Licensure - Certification - Credentialing

In the US, IONM licensure has not been legislated at the state or federal level. Issues of licensure are discussed in ASET's 68 page White Paper on Occupation Regulation. Worldwide, there are at least two private certifications available: the technologist level CNIM and the professional level D.ABNM. Though not governmentally regulated, certain health care facilities have internal regulations pertaining to neuromonitoring certifications. The more fundamental issue is that demand for trained intraoperative neurophysiologists continues to be greater than their number (2007).

Certification for Neurophysiological Intraoperative Monitoring

The CNIM [1] is awarded by the American Board of Electroencephalographic and Evoked Potential Technicians [2]. As of 2007-02, minimum requirements include 1) a B.A., B.S. or another health care credential, and 2) an experience base of 100 surgeries. ABRET has scheduled for 2008 major changes to these requirements. The $350, 250 question, 4 hour multiple choice written exam is offered twice a year.

Diplomate of the American Board of Neurophysiologic Monitoring

The D.ABNM [3] is awarded by the American Board of Neurophysiological Monitoring [4]. As of 2007-02, minimum requirements include 1) an M.S. or M.A. in a science related field, 2) an experience base of 300 surgeries that spans at least 3 years of primary responsibility, and 3) two surgeon-signed attestation forms. The exam includes a written portion, which must be passed first, and an oral portion. The $600, 250 question, 4 hour written exam is offered twice a year, as is the $800 oral exam. As 2007-02, there are 104 D.ABNM certified individuals.


Neuromonitoring employs the use of various electrophysiological techniques or modalities to record spontaneous and elicited signals from the patient's nervous system during surgery. Changes in these signals preceed permenant injury to the generating nervous tissue thus allowing detection of early or impending injury and providing a window of time for intervention. Modalities used in IONM have expanded over time and include but are not limited to somatosensory evoked potentials, motor or muscle evoked potentials, EEG, EMG and auditory brainstem response. Those used in any particular surgery depending on what portion of the nervous system is at risk. Electrodes are attached to the patient, which lead to a computer where a trained neurophysiologist can observe the results.

In general, a trained neurophysiologist attaches a computer system to the patient using stimulating and recording electrodes. Interactive software running on the system carries out 2 tasks. The system 1) selectively activates stimulating electrodes with appropriate timing, and 2) processes and displays the electrophysiologic signals as they are picked up by the recording electrodes. The neurophysiologist can thus observe and document the electrophysiologic signals in realtime in the operating during the surgery. The signals change according to a various factors, including anesthesia, tissue temperature, surgical stage, and tissue stresses. Various factors exert their influence on the signals with various tissue-dependent timecourses. Differentiating the signal changes along these lines - with particular attention paid to stresses - is the joint task of the surgical triad: surgeon, anesthesiologist, and neurophysiologist.

Transcranial doppler imaging is becoming more widely used to detect vascular emboli. TCDI can be used in tandem with EEG during vascular surgery.

IONM techniques have significantly reduced the rates of morbidity and mortality without introducing additional risks. By doing so, IONM techniques reduce health care costs.

Surgical Procedures

Patients benefit from neuromonitoring during certain surgical proceedures, including:

  • acoustic neuroma
  • anterior cervical diskectomy
  • anterior corpectomy
  • anterior vertebrectomy
  • arteriovenous malformations
  • brachial plexus or distal peripheral nerve injury
  • cardiopulmonary bypass and hypohermia
  • carotid body tumor
  • carotid endarterectomy
  • cauda equina tumors
  • cerebral and spinal aneurysms
  • cervical laminectomy
  • cochlear implant
  • correction of coarctation
  • cranial base tumors
  • DBS - deep brain stimulation
  • embolization of traumatic cavernous sinus fistula
  • epilepsy surgery (localization and mapping of eloquent cortex)
  • extracranial vascular reconstruction
  • femoral lengthening
  • fronto-temporal tumors (motor cortex mapping)
  • glomus tumor
  • instrumentation for spinal instability
  • intramedullary or extramedullary spinal cord tumors
  • lumbosacral decompression
  • microvascular decompression
  • neuroma-in-continuity
  • occlusion of brain-supplying arteries
  • parotidectomy
  • pedicle and lateral mass screw placement
  • pelvic hip arthroplasty
  • percutaneous transluminal angioplasy
  • peripheral nerve surgery
  • posterior fossa tumors
  • pterygian band release
  • radical head & neck surgery
  • repair of thoracic aortic aneurysm
  • revision mastoidectomy
  • rhizotomy/ganglionectomy
  • scoliosis correction
  • selective dorsal rhizotomy
  • spinal angiography
  • spinal arteriovenous malformations
  • spinal cord untethering
  • spinal fusion
  • stabilization of odontoid/dens fracture
  • subclavian-carotid bypass
  • syringomyelia
  • temporo-parietal tumors
  • thermal capsulorrhaphy
  • thoracic laminectomy
  • thyroidectomy
  • vestibular nerve section

Related Acronyms

Sort the acronym table by clicking on the header widgets:

Surg ACDF Anterior cervical decompression and fusion
Surg TLIF Transforaminal lumbar interbody fusion
Surg PLIF Posterior lumbar interbody fusion
Org ABRET American Board of Registration of Electroencephalographic and Evoked Potential Technologists
Org ASET American Society of Electroneurodiagnostic Technologists
Org ASNM American Soc of Neurophysiologic Monitoring
Org ABNM American Board of Neurophysiologic Monitoring
Org IFCN International Federation of Clinical Neurophysiology
Org WSET Western Society of Electrodiagnostic Technologists
Org AAAET American Association of Electrodiagnostic Technologists

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