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Archive for the ‘Surgical Neurophysiology’ Category

The Full IONM Lecture: Saphenous Nerve Somatosensory Evoked Potentials for the Reduction of Femoral Nerve Injury during Lateral Access Surgery

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The xtreme lateral/ transpsoas approach is a new minimally invasive surgical access technique to achieve a discectomy and interbody fusion. This technique has been promoted as being made safe by the application of a specific intra-operative neurophysiological protocol involving direct stimulus and recording of lower extremity EMG responses. Despite this technique, we continued to see post-op nerve injuries, especially when working on the L4-5 level.

Given the nature of this approach, we felt that the nerve injury was less a result of direct trauma but more a prolonged compression causing nerve ischemia. With EMG monitoring, this type of injury may not be seen. Loss of distal sensation may be the most sensitive measure of nerve pressure and ischemia (think of your leg “falling asleep” after sitting too long.) By monitoring the loss of sensation in the leg, we may be able to pick up this injury before it happens.

We sought to improve the safety of this procedure by having a more sensitive measure of the compression of the femoral nerve. Knowing the anatomy of this nerve, the saphenous branch of the femoral nerve is a distal SENSORY continuation of the femoral nerve. By monitoring the “SSEP” of this nerve, we can, in theory, monitor the femoral nerve as it courses through the psoas muscle.

Saphenous Nerve Somatosensory Evoked Potentials: Technique and Application for the Reduction of Femoral Nerve Injury during Lateral Access Surgery

Justin Silverstein, MS, CNIM, Spine Medical Services,  Clinical Neurophysiology, Commack, NY

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Saphenous SSEP

Posted with kind permission of the author. Copyright © 2013 – All Rights Reserved by Justin Silverstein

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Reliability of Triggered EMG for Prediction of Safety during Pedicle Screw Placement in Adolescent Idiopathic Scoliosis Surgery

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Study Design

We performed a prospective study to evaluate the reliability of using triggered electromyography (EMG) for predicting pedicle wall breakthrough during the placement of pedicle screw in adolescent idiopathic scoliosis surgery.


We wanted to correlate pedicle wall breakthrough with the triggered EMG threshold of stimulation and the postoperative computed tomography (CT) findings.

Overview of Literature

Pedicle wall breakthrough has been reported to be difficult to evaluate by radiographs. Triggered EMG had been found to be a more sensitive test to detect this breakthrough.


Seven patients who underwent the insertion of 103 pedicle screws were evaluated. The triggered EMG activity was recorded from several muscles depending on the level of screw placement. The postoperative CT scans were read by a spine surgeon who was a senior fellow in orthopedics, and a musculoskeletal radiologist.


The mean age at surgery was 12.6 years (range, 11 to 17 years). The preoperative mean Cobb angle was 54.7° (range, 45 to 65°). There were 80 thoracic screws and 23 lumbar screws. All the screws had stimulation thresholds of ≥ 6 mA, except 3 screws with the stimulation threshold of < 6 mA. Ten screws (9.7%) showed violation of the pedicle wall on the postoperative CT scans. Five screws penetrated medially and another five penetrated laterally. No postoperative neurologic complications were noted in any of the seven patients.


Measuring the stimulation threshold of triggered EMG helps to assess the pedicle screw placement. Pedicle screws that had stimulation threshold of ≥ 6 mA were safe, with 90.3% reliability, as was assessed on the postoperative CT scans.

Full article PDF view and download:Reliability of Triggered EMG for Prediction of Safety during Pedicle Screw Placement in Adolescent Idiopathic Scoliosis Surgery

Keywords: Adolescent idiopathic scoliosis, Pedicle screw, Triggered electromyography


Asian Spine J. 2011 March; 5(1): 51–58.
Published online 2011 March 2. doi:  10.4184/asj.2011.5.1.51 PMCID: PMC3047898
Reliability of Triggered EMG for Prediction of Safety during Pedicle Screw Placement in Adolescent Idiopathic Scoliosis Surgery
Woo-Kie Min, Hyun-Joo Lee, Won -Ju Jeong, Chang-Wug Oh, Jae-Sung Bae, Hwan-Seong Cho, In-Ho Jeon, Chang-Hyun Cho, and Byung-Chul Park
Copyright © 2011 by Korean Society of Spine Surgery
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited

Intraoperative Neurophysiologic Sensorimotor Mapping

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Intraoperative Neurophysiologic Sensorimotor Mapping-A Review
Mirela V. Simon*
Department of Neurology, Massachusetts General Hospital, Harvard Medical School, 55 Fruit St, Boston

The main goal of neurological surgery for supratentorial lesions remains maximal resection with preservation of function of the nearby eloquent cortical and subcortical structures. Many authors [1-9] have emphasized the positive impact of aggresive removal of gliomas on the survival rate and the quality of life in both adults and children. Others [10-12] have found a positive correlation between incomplete resection of an epileptic focus and poor seizure control outcome in epilepsy surgery.

However, maximal resection of supratentorial lesions is in many circumstances difficult to achieve due to the close proximity of functionally normal eloquent cortex. Despite advanced neuroimaging techniques and sensitive microscopes, visual inspection has often suboptimal resolution for distinguishing between normal and abnormal tissue, especially in cases of distorted anatomy and infiltrative pathology. More so, abnormal brain tissue, as appreciated by visual inspection, can retain normal function [13-15]. Thus, functional cortical mapping is essential for safe resection of lesions in the vicinity of eloquent cortex. This usually entails a multimodality approach, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), diffusion tensor imaging (DTI) and neurophysiologic studies as well as co-registration techniques that optimally utilize all the available data [16,17].

This article offers an overview of the neurophysiologic sensorimotor mapping. Probably one of the most important advantage this method has over the neuroimaging techniques is allowing live assessment of the cortical function and direct intraoperative feedback to the surgeon. Unlike fMRI, neurophysiologic techniques also allow subcortical mapping [18] and continuous monitoring of the sensorimotor pathways during the actual resection; also, its results are much less affected by the perilesional hemodynamic changes. Last, neurophysiologic mapping offers increased localizing specificity, when compared to other techniques [19,20].

Sensorimotor neurophysiologic mapping consists of two parts: first, contralateral (to the craniotomy side) median somatosensory evoked potentials (SSEPs) phase reversal technique is employed with the attempt to localize the central sulcus (CS). Identification of the latter reveals to the surgeon and neurophysiologist the presumed location of the primary motor cortex. In the second part of the motor mapping, the surgeon stimulates the precentral regions, in order to identify the motor strip. Direct electrical stimulation is applied subdurally or epidurally and triggered muscle motor evoked responses (mMEPs) and/or evoked clinical responses are recorded and/or observed in the contralateral hemibody muscles in anesthetized or awake patients. Triggered responses at the lowest current amplitude will help delineate the primary motor cortex. Additionally, once the motor strip is identified, its continuous stimulation allows monitoring of the primary cortex and corticospinal tract throughout the resection. Similarly, recording of the thalamocortical SSEPs helps identification of the somatosensory cortex and monitoring of the large fiber sensory pathways during lesionectomy. Last, in awake patients, somatosensory cortex can be further delineated by eliciting sensory symptoms by electrical stimulation of the postcentral regions.

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*Corresponding author: Mirela V Simon, WACC 739 G, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, 55 Fruit St, Boston, MA 02114, Tel: 617 724-2655; Fax: 617 724-6513; E-mail:
Citation: Simon MV (2011) Intraoperative Neurophysiologic Sensorimotor Mapping-A Review. J Neurol Neurophysiol S3. doi:10.4172/2155-9562.S3-002
Copyright: © 2011 Simon MV. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Neuroanesthesia management of 30 hour neurosurgery brainstem tumor requiring neurophysiology monitoring IONM iMRI OT

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Neuroanesthesia management of neurosurgery of brain stem tumor requiring neurophysiology monitoring in an iMRI OT setting

Read this amazing case report describing the operative and neuroanesthesia management of a rare case of ventrally exophytic pontine glioma:

It was guided by a new intraoperative neuromonitoring, which demanded some modifications in anesthesia management, such as, elimination of muscle relaxants and certain drugs used in neuroanesthesia. Also the presence in the special environment of the brainSUITE® intra-operative magnetic resonance imaging operating theater (iMRI OT) demands magnetic precautions and close monitoring of the patient’s welfare.

The time taken for this rare surgical procedure was 30 hours. Prolonged anesthesia time 38 hours in two stages (surgery monitoring of Brain Stem/MRI session).

by Abdulrahmam J. Sabbagh, Mahmoud Al-Yamany, Reem F. Bunyan,1 Mohamad S. M. Takrouri,2 and Sabry Mohammed Radwan2


This report describes a rare case of ventrally exophytic pontine glioma describing operative and neuroanesthesia management. The combination of intraoperative neuromonitoring was used. It constituted: Brain stem evoked responses/potentials, Motor EP: recording from cranial nerve supplied muscle, and Sensory EP: Medial/tibial. Excision of the tumor was done with intra-operative magnetic resonance imaging (iMRI), which is considered a new modality.

Keywords: Brain stem, brainSUITE® intra-operative magnetic resonance imaging operating theater, evoked responses/potentials, neuromonitoring, neuroanesthesia, Motor EP: Recording from cranial nerve supplied muscle, Sensory EP: Medial/tibial

Copyright © Saudi Journal of Anaesthesia

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Saudi J Anaesth. 2009 Jul-Dec; 3(2): 91–93.
doi:  10.4103/1658-354X.57877
PMCID: PMC2876938

Written by Neuro News

October 3, 2012 at 5:48 pm

A review of intraoperative monitoring for spinal surgery

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Effect of Warning on the Probability of an InjurySurg Neurol Int 2012,  3:174

A review of intraoperative monitoring for spinal surgery

Mark M Stecker
Department of Neuroscience, Winthrop University Hospital, Mineola, NY, USA

DOI: 10.4103/2152-7806.98579



Background: Intraoperative neurophysiologic monitoring (IONM) is a technique that is helpful for assessing the nervous system during spine surgery.
Methods: This is a review of the field describing the basic mechanisms behind the techniques of IONM. These include the most often utilized trancranial motor evoked potentials (Tc-MEPs), somatosensory evoked potentials (SSEPs), and stimulated and spontaneous EMG activity. It also describes some of the issues regarding practices and qualifications of practitioners.
Results: Although the anatomic pathways responsible for the Tc-MEP and SSEP are well known and these clinical techniques have a high sensitivity and specificity, there is little published data showing that monitoring actually leads to improved patient outcomes. It is evident that IONM has high utility when the risk of injury is high, but may be only marginally helpful when the risk of injury is very low. The monitoring team must be well trained, be able to provide the surgeon feedback in real time, and coordinate activities with those of the surgical and anesthesia teams.
Conclusions: Although IONM is a valuable technique that provides sensitive and specific indications of neurologic injury, it does have limitations that must be understood. Maintaining a high quality of practice with appropriately trained personnel is critical.

Keywords: Intraoperative neurophysiologic monitoring, motor evoked potentials, somatosensory evoked potentials, spine

Click here and read the full length article: review of intraoperative monitoring for spinal surgery

© 2012 Stecker; This is an open-access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Stecker MM. A review of intraoperative monitoring for spinal surgery. Surg Neurol Int 2012;3, Suppl S3:174-87

A medico-legal review of cases involving quadriplegia following cervical spine surgery: Is there an argument for a no-fault compensation system?

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Surg Neurol Int 2010,  1:3

A medico-legal review of cases involving quadriplegia following cervical spine surgery: Is there an argument for a no-fault compensation system?

Nancy E Epstein
Clinical Professor of Neurological Surgery, The Albert Einstein College of Medicine, Bronx, NY, USA and Chief of Neurosurgical Spine and Education, Winthrop University Hospital, Mineola, NY, USA

© 2010 Epstein; This is an open-access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.4103/2152-7806.62261

PMID: 20657685


Background: To determine whether patients who become quadriplegic following cervical spine surgery are adequately compensated by our present medico-legal system. The outcomes of malpractice suits obtained from Verdict Search (East Islip, NY, USA), a medico-legal journal, were evaluated over a 20-year period. Although the present malpractice system generously rewards many quadriplegic patients with substantial settlements/Plaintiffs’ verdicts, a subset receive lesser reimbursements (verdicts/settlements], while others with defense verdicts receive no compensatory damages.
Methods: Utilizing Verdict Search, 54 cases involving quadriplegia following cervical spine surgery were reviewed for a 20-year interval (1988-2008). The reason(s) for the suit, the defendants, the legal outcome, and the time to outcome were identified. Operations included 25 anterior cervical procedures, 22 posterior cervical operations, 1 circumferential cervical procedure, and 6 cases in which the cervical operations were not defined.
Results: The four most prominent legal allegations for suits included negligent surgery (47 cases), lack of informed consent (23 cases), failure to diagnose/treat (33 cases), and failure to brace (15 cases). Forty-four of the 54 suits included spine surgeons. There were 19 Plaintiffs’ verdicts (average US $5.9 million, range US $540,000-US $18.4 million), and 20 settlements (average US $2.8 million, range US $66,500-US $12.0 million). Fifteen quadriplegic patients with defense verdicts received no compensatory damages. The average time to verdicts/settlements was 4.3 years.
Conclusions: For 54 patients who were quadriplegic following cervical spine surgery, 15 (28%) with defense verdicts received no compensatory damages. Under a No-Fault system, quadriplegic patients would qualify for a “reasonable” level of compensation over a “shorter” time frame.

Keywords: Cervical spine surgery, Quadriplegia, Medico-legal liability suits, No-fault system, Intraoperative Neurophysiological Monitoring

Read Full Article: A medico-legal review of cases involving quadriplegia following cervical spine surgery: Is there an argument for a no-fault compensation system?

Is the Cost of Neuromonitoring with Motor Evoked Potentials for Scoliosis Surgery Justified?

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Cobb angle measurement of a scoliosis; concave...

Cobb angle measurement of a scoliosis; concave side on the left; convex side on the right (Photo credit: Wikipedia)

“Intraoperative traction is associated wit frequent abnormalities in TcMep monitoring. The thoracic location of the major curve, mean Cobb angle of 86 degrees, and increased rigidity are risk factors for changes in TcMep monitoring with traction. The presence of any TcMep recordings at closure was associated with normal neurological function. Somatosensory evoked potentials should not be used as the sole means of scoliosis monitoring.”

The presence of any TcMep recordings at closure was associated with normal neurological function. Somatosensory evoked potentials alone is insufficient in accurately monitoring scoliosis correction.

There are more than 2 million annual surgeries in the U.S. alone where nerve damage is a major risk, representing an annual global revenue opportunity in excess of $500 million.

Kuklo, Timothy R. MD, JD (Washington University School of Medicine); Polly, David W. MD; Diab, Mohammad MD

Level of Evidence: II

Introduction: To analyze societal costs of routine neuromonitoring in deformity surgery versus the potential societal costs of spinal cord injury from an adverse surgical event in terms of malpractice settlements and lifetime patient care needs.

Methods: A national database of personal injury verdicts/awards (Westlaw) was searched to determine the average settlement after an adverse outcome following spinal surgery in the past 10 yrs, regardless of fault. Lifetime patient care needs were also determined, based on age at injury/life expectancy. 4,000 spinal deformity cases/yr in the US at a neural injury rate of .03% were assumed for analysis. The cost of neuromonitoring was determined to be $190/hr based on review of 2 separate hospital contract rates (mean $950/case). Search terms included spine surgery, scoliosis, paraplegia and neurologic injury yielded 110 potential cases, of which there were 43 defense verdicts, 22 cases determined to be n/a, and 27 injuries determined not to be related to surgery.

Results: The database yielded 18 cases of neural injury in spine surgery, of which 6 were deformity operations (ave. age 16.6 yrs) having an average verdict of $11.9 million (range $2.9–25.0 mil). The other 12 cases (ave $754,000 payout) did not involve spinal deformity. This also did not include an evaluation of settlements prior to trial, where payout of a typical structured settlement may be 1.5–5 times the final settlement. The estimated cost of neuromonitoring was $950/case X 4000, or $3.8 million/yr. Assuming a false negative rate of MEPs at ˜0.25% and an inability to monitor 10% of cases, potentially 3 cases/yr of paraplegia would be avoided with complete neuromonitoring (SSEP, MEP, EMG).

Conclusion: Assuming 12 cases of neurologic injury/yr (.03% of 4000 cases) not including other non‐paraplegic neurologic injuries and pre‐trial settlements, and with monitoring at $950/case ($3.8 mil/yr), a conservative estimate of societal savings would be over $30–40 mil/yr of direct costs ‐ hence insurance reimbursement of neuromonitoring services should be mandatory.

Spine: Affiliated Society Meeting Abstracts:
23–26 September 2009 – Volume 10 – Issue – p 108
Scientific Program Abstracts
Read more about the benefits of intraoperative neurophysiological monitoring:

‘The National Monitor’ : Pushing IONM from medical room to mainstream

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Black and white photograph of a Neumann U87 mi...

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‘Surgical Neurophysiology and Neuromonitoring’ launches a new outlet called The National Monitor hosted by Michael Wilkins.  The National Monitor will increase the exposure of IONM through constructive discussions and articles that will break down the roadblocks that hold IONM expansion back. Read on to learn more.

One will quickly realize a clear trend from my writing, I like to connect creativity with innovation and this includes getting the word out about promising prospects.  Every industry faces unique challenges and nothing short of a campaign on the behalf of its members to tackle them.  Consider this: IONM came into existence over 20 years ago in the United States and yet, as some IONM professionals simply put it “You cannot simply walk into any room and start talking about our profession without giving a brief overview of IONM.”  Oftentimes what we need is not so much to be taught as to be reminded of what we already know.  IONM’s main issue is exposure.  Pushing IONM from medical room to mainstream will happen eventually, but instead of waiting for time to tick by, the proactive efforts of our community can hasten the progression.

The issue of exposure is rather the summation of several underlying challenges that must be resolved to open IONM to further prosperity and relevancy to Main Street.  So I pose the question to our readers:

What do you feel is/are the largest roadblocks in the expansion of IONM within the US healthcare system? 

This question will nonetheless have a different answer from each person though its relevancy to the IONM industry is undeniable. Seeing the issue through the lens of each of our experiences can provoke insightful discussion of the main issues that need to be addressed.

This series will address IONM’s roadblocks but hopefully through this we shall be able to create resources along the way and shape IONM into a more clarified field.  As the discussion takes place, I will gather as much insight and ideas as they appear to fuel more comprehensive future articles.

I look forward to working with ‘Surgical Neurophysiology and Neuromonitoring’ and its readers to increase the exposure of the IONM industry.

IONM: Contributing to a lower cost, higher quality healthcare system

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Barack Obama signing the Patient Protection an...

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On Capitol Hill, from whispers to pure rage, the heated discussion of economic reform is the constant talk of congressional members and their staff.  Savings within the U.S. healthcare system have been one of the largest topics focused upon within this debate.

In a statement by Judiciary Committee Chairman Lamar Smith (2011), Congressman Smith pointed out that one of the largest contributions to raising healthcare costs is defensive medical practices.  Defensive medical practices have evolved as a means for practitioners to avert the possibility of malpractice suits.  Often the services or tests requested on the practitioner’s behalf avoid liability rather than benefiting the patient.  Essentially, the more tests provided, the better the practitioner’s defense in court and liability pre-empted.

Closer examination of neurological litigation reveals some startling statistics.  Scarrow et al. (2011) examined a neurosurgical claims database containing cases between January 2004 and June of 2009.  The researchers found that 70% of neurosurgical lawsuits concerned operations of the spine.  Further broken down, 54% of the cases involved the lumbar spine, 37% the cervical spine, and 9% the thoracic.  Within Scarrow’s review “the average cost to defend all claims was $86,882, with an average [settlement] of $392,433.  Of all the cases, 70% of the plaintiffs alleged improperly performed surgery.  This 70% is exactly where the utilization of IONM can truly drive down the costs of rising malpractice costs for neurosurgical practitioners. IONM can reduce the frequency of claims and help avoid detrimental mistakes before they translate into medical costs.

Certain preventative practices like IONM are still unknown to many healthcare policymakers. The ability to bridge the divide between policymakers and expanded IONM utilization is not that large.  IONM has large potential to be considered a preventative measure under the recently passed Patient Protection and Affordable Care Act of 2010.  Under Title 4, Section 4003, the law calls for the creation of an independent Preventive Services Task Force to be comprised of a selected number of non-federal health experts.  These members “shall review the scientific evidence related to the effectiveness, appropriateness, and cost-effectiveness of….preventive services”.  Though neither IONM, nor any other preventative procedure is referenced, the recommendations of this group will have large implications for healthcare coverage.  As long as IONM is brought to the attention of the Task Force and other similar health bodies, the ability of IONM will surely be promoted and researched further.

As we move forward toward the full implementation of the Patient Protection and Affordable Care Act in 2014, it is in the best interest of the IONM community and the nation as a whole to advocate the proven value of IONM in preventative medicine.


Committee on the Judiciary (January 20, 2011). ‘Medical Liability Reform-Cutting Costs, Spurring Investment, Creating Jobs’. Press Release. Retrieved 2011-08-21.

Patient Protection and Affordable Health Care Act of 2010, 4 U.S.C. §4003 (2011). Retrieved 2011-08-21.

Scarrow, Zusman, Ball, Wehby, (2011). Review of Closed-Claim Malpractice Litigation in Neurosurgery.
AANS Neurosurgeon, Vol. 20, Number 1. Retrieved 2011-08-21.

Intraoperative Neurophysiological Monitoring, preventative medicine, neuromonitoring, Affordable Care Act, Neurosurgery, Lawsuits,

What is surgical neurophysiology? What is IONM?

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Surgical Neurophysiology

What is surgical neurophysiology?
Surgical neurophysiology, also known as intraoperative neurophysiology monitoring (IONM), is a new and growing allied health field. The surgical neurophysiologist is an integral part of the surgical team, and works closely with the anesthesiologist or anesthetist, the surgeons, and other members of the team. The neurophysiologist performs testing and monitoring of the nervous system during surgery to assist the surgeons in avoiding or reducing complications such as paralysis, hearing loss, or stroke (depending on the type of surgery), by detecting incipient injury in time to prevent or ameliorate it. Surgical neurophysiology also provides information to the surgeon for use in intraoperative decision-making.

What kinds of surgeries can be monitored?
Surgical neurophysiology monitoring employs a wide variety of modalities, each with a very specific application. It is most applicable when there is a specific risk to some part of the nervous system. For some types of surgery, such as cerebellar tumors, there is no suitable monitoring technique. Some of the most commonly monitored surgeries include spinal surgery, certain types of brain surgery, some ENT procedures, peripheral nerve surgery, and vascular surgeries such as carotid endarterectomies and thoracic-abdominal aortic aneurysms (TAAA).

What testing modalities are performed in intraoperative monitoring?
Many different modalities can be used in the OR. Frequently several modalities, such as SSEP, EMG and MEP (see below) are used together in the same surgery. Some of the most widely used modalities include:

  • SSEP (Somatosensory Evoked Potentials)—the response recorded from the brain, nerve, or spinal cord to electrical stimulation of peripheral nerve. Used most often to monitor the integrity of the dorsal columns of the spinal cord during spine surgery; also used in some brain surgeries and peripheral nerve surgeries.
  • TCeMEP ( Transcranial Electrical Motor Evoked Potentials): an electrical stimulus is applied to the motor cortex of the brain, and a response recorded from the spinal cord or from limb muscles. Works like SSEP (see above), but in the opposite direction, to monitor function of the motor tracts of the spinal cord.
  • BSEP (Brainstem Auditory Evoked Potentials)—an electrical response, originating in the brainstem, to an auditory stimulus, usually a click delivered through small in-the-ear earphones. Used to monitor brainstem function and to help preserve hearing in acoustic neuroma and brainstem tumor cases.
  • EMG (electromyography)—spontaneous EMG is used to detect incipient nerve damage in spine surgery (spinal nerve roots) and in skull base surgery (facial nerve and other cranial nerves). Evoked EMG, using an electrical stimulus delivered through a hand-held probe used by the surgeon, is also used to identify and test nervous structures.
  • Pedicle Screw Stimulation: evoked EMG obtained by stimulating a screw placed in part of a vertebra called the pedicle. Since a nerve root lies immediately beneath each pedicle, a response obtained at too low a stimulus intensity level indicates a breach in the pedicle. Used to avoid nerve root damage caused by such a breach.
  • EEG (Electroencephalogram)—spontaneous brain activity is recorded to monitor functional integrity of the cerebral cortex, specifically to avoid injuries caused by ischemia (reduced blood flow) during carotid endarterectomies and aneurysm clippings.
  • ECOG (Electrocorticography)—EEG recorded directly from the exposed surface of the brain to help define the borders of resection (tissue removal) in epilepsy surgeries and craniotomies for brain tumors.
  • Direct Cortical Stimulation: Also used in epilepsy and tumor surgeries, to identify and map eloquent areas of the brain (speech and motor areas)
  • TCD (Transcranial Doppler)—blood flow velocity in the internal arteries of the brain is measured using an ultrasound beam, analogous to clocking a baseball pitch with a radar gun. Used to monitor cerebral blood flow in carotid endarterectomies.

Who are surgical neurophysiologists?
Surgical neurophysiology, though rapidly evolving into an established profession, began as an interdisciplinary field. Neurophysiologists come from a variety of backgrounds, including medicine (especially neurology and physiotry); audiology; neuroscience; and neurodiagnostic technology.

How did surgical neurophysiology develop?
The earliest intraoperative neurophysiology was probably the famous work of Wilder Penfield and others in the 1920’s. Penfield mapped exposed motor and speech cortex by electrical stimulation. In the 1960’s and 1970’s, EEG recordings were made from exposed cerebral cortex in epilepsy and tumor surgeries.

In the 1970’s, following the development of commercial evoked potential equipment, SSEP was used to prevent paralysis in scoliosis surgeries; BSEP and facial nerve EMG began to be used in skull base surgeries at about this time to prevent facial paralysis and hearing loss, and EEG monitoring began to be used in carotid endarterectomies to prevent ischemic strokes during surgery. The use of SSEP monitoring has become generalized to a wide variety of spinal and other surgeries, and some form of intraoperative neurophysiology monitoring has become the standard of care in many types of surgeries.

With the widespread popularity of several modalities of IONM, the specialty began to emerge as neurophysiologists, audiologists, technologists and others began to develop the skills to perform multiple types of monitoring. The technology has steadily improved, the knowledge base has greatly expanded with research and clinical experience, and new applications have been developed. The most recent major advance in the field has been the development of transcranial electric motor evoked potential (TCeMEP) monitoring.

Where is surgical neurophysiology headed in the future?
Surgical neurophysiology continues to advance, with the development of new applications such as brainstem mapping, spinal cord mapping, monitoring for position-related nerve injuries, and many others. The surgical neurophysiologist requires increasing knowledge, versatility and sophistication. The greatest challenge faced by this evolving field is the need for standardized education, training and credentialling. Many neurophysiologists envision a structure like that of audiology, with graduate degrees in the field and state licensure.

© Copyright, 2004. Jerry Larson, CNIM, D. ABNM,



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