Description:
Magnetoencephalography (MEG) is a noninvasive functional imaging technique that records weak magnetic forces. When this information is superimposed on an anatomic image of the brain, typically a magnetic resonance imaging scan, the image is referred to as magnetic source imaging (MSI). MSI has been used to localize epileptic foci and to identify "eloquent" areas of the brain for neurosurgical planning.

For individuals who have drug-resistant epilepsy and are being evaluated for possible resective surgery who receive MEG/MSI, the evidence for MEG/MSI as an adjunct to standard clinical workup includes various types of case series. Relevant outcomes are test accuracy and functional outcomes. Published evidence on MEG is suboptimal, with no clinical trials demonstrating clinical utility. Literature on diagnostic accuracy has methodologic limitations, primarily selection and ascertainment bias. Studies of functional outcomes do not fully account for the effects of MEG, because subjects who received MEG were not fully accounted for in the studies. The evidence is insufficient to determine the effects of the technology on health outcomes. 

For individuals who have brain lesions and a planned brain resection who receive MEG/MSI, the evidence for MEG/MSI for localization of eloquent function areas includes comparative studies. Relevant outcomes include test accuracy and functional outcomes. Available studies have reported that this test has high concordance with the Wada test, which is currently the main alternative to localize eloquent functions. Management is changed in some patients based on MEG testing, but it has not been demonstrated that these changes lead to improved outcomes. The evidence is insufficient to determine the effects of the technology on health outcomes.

Background  
MAGNETOENCEPHALOGRAPHY
Magnetoencephalography (MEG) is a noninvasive functional imaging technique that records weak magnetic forces associated with brain electrical activity. Using mathematical modeling, recorded data are then analyzed to provide an estimated location of electrical activity. This information can be superimposed on an anatomic image of the brain, typically a magnetic resonance imaging (MRI) scan, to produce a functional/anatomic image of the brain, referred to as magnetic source imaging (MSI). The primary advantage of MSI is that, while conductivity and thus measurement of electrical activity as recorded by electroencephalogram is altered by surrounding brain structures, magnetic fields are not. Therefore, MSI permits a high-resolution image. 

Detection of weak magnetic fields requires gradiometer detection coils coupled to a superconducting quantum interference device, which requires a specialized room shielded from other magnetic sources. Mathematical modeling programs based on idealized assumptions are then used to translate detected signals into functional images. In its early evolution, clinical applications were limited by the use of only one detection coil requiring lengthy imaging times, which, because of body movement, also were difficult to match with the MRI. However, more recently, the technique has evolved to multiple detection coils in an array that can provide data more efficiently over a wide extracranial region.  

Applications
One clinical application is localization of epileptic foci, particularly for screening of surgical candidates and surgical planning. Alternative techniques include MRI, positron emission tomography, or single photon emission computed tomography scanning. Anatomic imaging (i.e., MRI) is effective when epilepsy is associated with a mass lesion, such as a tumor, vascular malformation or hippocampal atrophy. If an anatomic abnormality is not detected, patients may undergo a positron emission tomography scan. In a small subset of patients, extended electrocorticography or stereotactic electroencephalography with implanted electrodes is considered the criterion standard for localizing epileptogenic foci. MEG/MSI has principally been investigated as a supplement to or an alternative to invasive monitoring.

Another clinical application is localization of the pre- and postcentral gyri as a guide to surgical planning in patients scheduled to undergo neurosurgery for epilepsy, brain neoplasms, arteriovenous malformations, or other brain lesions. These gyri contain the "eloquent" sensorimotor areas of the brain, the preservation of which is considered critical during any type of brain surgery. In normal situations, these areas can be identified anatomically by MRI, but frequently, anatomy is distorted by underlying disease processes. In addition, location of eloquent functions varies, even among healthy people. Therefore, localization of the eloquent cortex often requires such intraoperative invasive functional techniques as cortical stimulation with the patient under local anesthesia or somatosensory-evoked responses on extended electrocorticography. Although these techniques can be done at the same time as the planned resection, they are cumbersome and can add up to 45 minutes of anesthesia time. Furthermore, these techniques can sometimes be limited by the small surgical field. A preoperative test, which is often used to localize the eloquent hemisphere, is the Wada test. MEG/MSI has been proposed as a substitute for the Wada test.

Regulatory Status 
The U.S. Food and Drug Administration (FDA) regulates MEG devices as class II devices cleared for marketing throughthe 510(k) process. The FDA product codes OLX and OXY are used to identify the different components of the devices.OLX-coded devices are source localization software for electroencephalography or MEG; the software correlates theelectrical activity of the brain using various neuroimaging modalities. This code does not include electrodes, amplitude-integrated electroencephalography, automatic event-detection software used as the only or final electroencephalographanalysis step, electroencephalography software with comparative databases (normal or otherwise), orelectroencephalography software that outputs an index, diagnosis or classification.

OLY-coded devices are magnetoencephalographs that acquire, display, store, and archive biomagnetic signals producedby electrically active nerve tissue in the brain to provide information about the location of active nerve tissue responsiblefor certain brain functions relative to brain anatomy. This includes the magnetoencephalograph recording device (hardware, basic software).

The intended use of these devices is to "non-invasively detect and display biomagnetic signals produced by electricallyactive nerve tissue in the brain. When interpreted by a trained clinician, the data enhance the diagnostic capability byproviding useful information about the location relative to brain anatomy of active nerve tissue responsible for critical brainfunctions."^1, More recent approval summaries add: "MEG is routinely used to identify the locations of visual, auditory,somatosensory, and motor cortex in the brain when used in conjunction with evoked response averaging devices. MEG isalso used to noninvasively locate regions of epileptic activity within the brain. The localization information provided byMEG may be used, in conjunction with other diagnostic data, in neurosurgical planning."^1,

The MagView Biomagnetometer System (Tristan Technologies) has the unique intended use for patient populations whoare neonates and infants and those children with head circumferences of 50 cm or less.²

Table 1 summarizes a sampling of relevant MEG devices (hardware, software). 

Table 1. Magnetoencephalography Devices Cleared by FDA (Product Codes OLX and OLY) 

EEG: electroencephalogram; FDA: Food and Drug Administration.

In 2000, Biomagnetic Technologies acquired Neuromag and began doing business as 4-D NeuroImaging. The latter company ceased operations in 2009.

Related Policies
60147 Functional Magnetic Resonance Imaging

Policy:
Magnetoencephalography/magnetic source imaging for the purpose of determining the laterality of language function, as a substitute for the Wada test, in patients being prepared for surgery for epilepsy, brain tumors, and other indications requiring brain resection, may be considered MEDICALLY NECESSARY.

Magnetoencephalography/magnetic source imaging as a part of the preoperative evaluation of patients with intractable epilepsy (seizures refractory to at least two first-line anticonvulsants) may be considered MEDICALLY NECESSARY when standard techniques, such as MRI and EEG, do not provide satisfactory localization of epileptic lesion(s).

Magnetoencephalography/magnetic source imaging is investigational and/or unproven and therefore is considered NOT MEDICALLY NECESSARY for all other indications.

Policy Guidelines
Please see the Codes table for details.

Benefit Application 
BlueCard/National Account Issues
Magnetoencephalography is available at a limited number of institutions. Therefore, magnetoencephalography may be identified by a request for an out-of-network referral.

State or federal mandates (e.g., FEP) may dictate that all devices approved by the U.S. Food and Drug Administration (FDA) may not be considered investigational. However, this policy considers specific applications of an FDA-approved device as investigational. Alternatively, FDA-approved devices may be assessed on the basis of their medical necessity.

Using a claims-based approach to this policy may make it difficult to distinguish between use that is considered medically necessary and use that is considered investigational. In general, the medically necessary use should be done at the time of preoperative testing. The investigational use would occur earlier in the clinical sequence before a decision about surgery is made. Some patients, e.g., those with seizures, could be candidates for both uses of this test.

Rationale 
This evidence review was created in December 1999 and has been updated regularly with searches of the PubMeddatabase. The most recent literature update was performed through July 29, 2020.

Evidence reviews assess whether a medical test is clinically useful. A useful test provides information to make a clinicalmanagement decision that improves the net health outcome. That is, the balance of benefits and harms is better when thetest is used to manage the condition than when another test or no test is used to manage the condition.

The first step in assessing a medical test is to formulate the clinical context and purpose of the test. The test must betechnically reliable, clinically valid, and clinically useful for that purpose. Evidence reviews assess the evidence onwhether a test is clinically valid and clinically useful. Technical reliability is outside the scope of these reviews, andcredible information on technical reliability is available from other sources.

Localization of Seizure Foci
Clinical Context and Test Purpose
The purpose of magnetoencephalography (MEG) and magnetic source imaging (MSI) in the mapping of epileptic foci is tofacilitate surgical treatment planning for persons with drug-resistant epilepsy.

The question addressed in this evidence review is: Does the use of MEG/MSI enhance localization of epileptic foci inconjunction with other noninvasive testing or replace invasive testing and, thus, result in changes in clinical managementand improvement in health outcomes?

The following PICO was used to select literature to inform this review.

Patients
The relevant population of interest is patients with drug-resistant epilepsy who are being evaluated for resective surgery.

Interventions
The intervention of interest is MEG/MSI used to map epileptic foci. MEG/MSI is primarily used as a preoperative adjunctto other noninvasive tests used in clinical practice for epileptic foci localization. These tests includeelectroencephalography (EEG), magnetic resonance imaging, positron emission tomography and single-photon emissioncomputerized tomography.

Comparators
The following practice is currently being used to make decisions about managing drug-resistant epilepsy: standardevaluation for seizure focus localization.

Outcomes
Outcomes of interest are diagnostic accuracy (e.g., test sensitivity and specificity) and clinical utility (e.g., consideration ofavoidance of invasive testing).

Technically Reliable
Assessment of technical reliability focuses on specific tests and operators and requires a review of unpublished and oftenproprietary information. Review of specific tests, operators and unpublished data are outside the scope of this evidencereview and alternative sources exist. This evidence review focuses on the clinical validity and clinical utility.

Clinically Valid
A test must detect the presence or absence of a condition, the risk of developing a condition in the future, or treatmentresponse (beneficial or adverse).

This section of the review is based on a TEC Special Report (2008) that reviewed the evidence on MEG for localization ofepileptic lesions.³ MEG has been proposed as a method for localizing seizure foci for patients with normal or equivocalmagnetic resonance imaging and negative video-electroencephalogram (EEG) examinations, so-called "nonlesional"epilepsy. Such patients often undergo MEG, positron emission tomography, or ictal single-photon emission computedtomography to localize the seizure focus. They then often undergo invasive intracranial EEG (IC-EEG), a surgicalprocedure in which electrodes are inserted next to the brain. Definitive proof that MEG is effective would be comparativeevidence that when compared with not using MEG, it improved patient outcomes. Such improvement in outcomes wouldinclude more patients being rendered seizure-free, use of a less invasive and morbid diagnostic workup and overallimproved patient outcomes. This is a complicated array of outcomes that have not been thoroughly evaluated in acomprehensive manner. Because MEG is used to make decisions regarding further diagnostic testing, which may affectthe decision to have surgery and the extent of surgery, solely examining surgical outcomes excludes the assessment ofoutcomes of patients who did not have surgery.

Ideally, a randomized trial comparing the outcomes of patients who receive MEG as part of their diagnostic workupcompared with patients who do not receive MEG could determine whether MEG improves patient outcomes. However,almost all of the studies evaluating MEG have been retrospective, where MEG, other tests, and surgery have been selectively applied to patients. Because patients often drop out of the diagnostic process before having IC-EEG, andmany patients ultimately do not undergo surgery, most studies of associations between diagnostic tests and betweendiagnostic tests and outcomes are biased by selection and ascertainment biases. For example, studies that evaluate thecorrelation between MEG and IC-EEG invariably do not account for the fact that MEG information was sometimes used todeselect a patient from undergoing IC-EEG. In addition, IC-EEG findings only imperfectly correlate with surgicaloutcomes, meaning that it is an imperfect reference standard.

Numerous studies have shown associations between MEG findings and other noninvasive and invasive diagnostic tests,including IC-EEG, and between MEG findings and surgical outcomes. However, such studies do not allow anyconclusions on whether MEG added incremental information to aid the management of such patients and whetherpatients' outcomes were improved as a result of the additional diagnostic information.

A representative study of MEG by Knowlton et al. (2008) demonstrated many of the problematic issues of evaluatingMEG.⁴ In this study of 160 patients with nonlesional epilepsy, all had MEG but only 72 proceeded to IC-EEG. Thecalculations of diagnostic characteristics of MEG are biased by incomplete ascertainment of the reference standard.However, even examining the diagnostic characteristics of MEG using the 72 patients who underwent IC-EEG,sensitivities, and specificities were well below 90%, indicating the likelihood of both false-positive and false-negativestudies. Predictive values based on these sensitivities and specificities mean that MEG can neither rule in nor rule out apositive IC-EEG and that MEG cannot be used as a triage test before IC-EEG to avoid potential morbidity in a subset ofpatients.

One study more specifically addressed whether MEG can improve the yield of IC-EEG, thus, allowing more patients toreceive surgery. In another study by Knowlton et al. (2009), MEG results modified the placement of electrodes in 18 (23%)of 77 patients who were recommended to have IC-EEG.⁵ Seven (39%) of 18 patients had positive intracranial seizurerecordings involving additional electrode placement because of MEG results. It was concluded that four (5%) patients werepresumed to have had surgery modified as a result of the effect of MEG electrode placement.

Section Summary: Clinically Valid
There are no clinical trials or other high-quality studies demonstrating the diagnostic accuracy of MEG in determining thelocation of seizure foci. Available evidence on diagnostic accuracy is limited by ascertainment and selection biasesbecause MEG findings were used to select and deselect patients in the diagnostic pathway, thus making it difficult todetermine the role of MEG for the purpose of seizure localization.

Clinically Useful
A test is clinically useful if the use of the results informs management decisions that improve the net health outcome ofcare. The net health outcome can be improved if patients receive correct therapy, or more effective therapy, or avoidunnecessary therapy, or avoid unnecessary testing.

Direct Evidence
Direct evidence of clinical utility is provided by studies that have compared health outcomes for patients managed withand without the test. Because these are intervention studies, the preferred evidence would be from randomized controlledtrials.

Several studies have correlated MEG findings with surgical outcomes. Lau et al. (2008) performed a systematic review of17 such studies.⁶ In this review, sensitivity and specificity had unorthodox definitions. Sensitivity was the proportion ofpatients cured with surgery in whom the MEG-defined epileptic region was resected, and specificity was the proportion ofpatients not cured with surgery in whom the MEG-defined epileptic region was not resected. Pooled sensitivity was 84%,meaning that, among the total number of cured patients, 16% occurred despite the MEG-defined region not beingresected. Pooled specificity was 52%, meaning that, among 48% of patients not cured, the MEG-localized region wasresected. Another more recent systematic review by Mouthaan et al. (2019) from the E-PILEPSY consortium which used amore conservative analytic approach to pool data from a smaller subset of studies found similar but slightly lower MSIsensitivity (79% vs. 84%) and specificity (46% vs. 52%).⁷ These results are consistent with an association between resection of the MEG-defined region and surgical cure but that it is an imperfect predictor of surgical success. However, itdoes not address the question of whether MEG contributed original information to improve the probability of cure. In aretrospective review of 22 children with medically intractable focal epilepsy (median age at epilepsy surgery, 11 years), Kim et al. (2013) used a cutoff of 70% or more for the number of MEG identified spike dipole sources located within theresection margin to define a positive study.⁸ Sensitivity, specificity and positive and negative predictive values forseizure-free status postoperatively were 67%, 14%, 63% and 17%, respectively.

Chain of Evidence
Indirect evidence on clinical utility rests on clinical validity. If the evidence is insufficient to demonstrate test performance, no inferences can be made about clinical utility.

Other studies have implied value of MEG but it is difficult to make firm conclusions regarding its value. In a study by Schneider et al. (2013), 14 patients with various findings on MEG, IC-EEG, and interictal single-photon emissioncomputed tomography underwent surgery for nonlesional neocortical focal epilepsy.⁹ Concordance between IC-EEG andMEG occurred in five patients, four of whom became seizure-free. This concordance of the two tests was the best predictor ofbecoming seizure-free. Although this was prognostic for success, whether this would actually change surgical decisionmaking, such as declining to operate where there is no such concordance, is uncertain. A similar study by Widjaja et al. (2013) showed that concordance between MEG findings and the location of surgical resection correlated with betterseizure outcomes.¹⁰ However, the authors acknowledged that MEG was entrenched in clinical practice, and the decisionto proceed further in diagnostic and therapeutic endeavors was based on results of MEG and other tests.

Other case series of surgical patients have suggested value to MEG. A study by Albert et al. (2014) reviewed a series ofpediatric patients undergoing surgery for epilepsy who had only undergone noninvasive monitoring prior to surgery.¹¹ MEG was proposed to have avoided the need for the morbidity associated with invasive monitoring. Of 16 patients, 62.5% were seizure-free following surgery, and 20% experienced improvement. Two cases required additional surgery withinvasive monitoring. Although most patients improved, it could not be determined whether the outcomes were equivalentto the standard practice of pre-resection invasive monitoring. A study by Wang et al. (2015) compared fluorine 18fluorodeoxyglucose positron emission tomography with MEG in identifying the epileptogenic zone, using invasivemonitoring as the reference standard.¹² Fluorodeoxyglucose positron emission tomography identified the zone in 8 (50%)of patients and MEG identified the zone in 12 (75%) of patients. Although MEG was more sensitive thanfluorodeoxyglucose positron emission tomography in this study, it still missed epileptogenic areas identified by invasivemonitoring. Another study, by Koptelova et al. (2013), compared MEG with video-EEG monitoring in 22 patients.¹³ Of 75 "irritative" zones identified in the 22 patients by either method, a higher proportion was identified by MEG. Note that thereis no true reference standard in this type of analysis. However, in analyses of intraoperative EEG, several zones identifiedonly with this method were only identified by MEG, confirming to some extent increased sensitivity over video-EEG.These recent studies have suggested clinical utility for MEG in the evaluation of epilepsy patients, but, due to theaforementioned problems, firm conclusions about the clinical utility of MEG cannot be determined.

The American Clinical Magnetoencephalography Society (2009) released a position statement that supported the routineclinical use of MEG/MSI for presurgical evaluation of patients with medically intractable seizures.¹⁴ This statement cited astudy by Sutherling et al. (2008) as being a "milestone class I study." Class I evidence usually refers to randomizedcomparisons of treatment. However, the authors of Sutherling et al. (2008) study described it as a "prospective, blinded crossover-controlled, single-treatment, observational case series."¹⁵ The study attempted to determine the proportion of patients in whom diagnostic or treatment strategy was changed as a consequence of MEG. They concluded the testprovided nonredundant information in 33% of patients, changed treatment in 9% of surgical patients, and benefited 21%of patients who had surgery. There was no control group in this study. The benefit of MEG was inferred by assumptions ofwhat might have occurred in the absence of MEG results. Less than half of 69 enrolled patients went on to receive IC-EEG; thus, there appeared to be incomplete accounting for outcomes of all patients in the study. A similar study by DeTiege et al. (2012) also attempted to determine the number of patients in whom management decisions were alteredbased on MEG results.^16, They concluded that clinical management was altered in 13% of patients.

Section Summary: Clinically Useful
Evidence supporting the effect of MEG on patient outcomes is indirect and incomplete. Surgical management may bealtered in a minority of patients based on MEG, but the evidence does not support the conclusion that outcomes areimproved as a result of these management changes. Trials with a control group are needed to determine whetherimproved outcomes can be attributed to the change in management induced by knowledge of MEG findings.

Localization of Eloquent and Sensorimotor Areas
Clinical Context and Test Purpose
The purpose of MEG/MSI in the localization of eloquent and sensorimotor areas of the brain in persons with cortical brainlesions is to create a precise surgical plan for resective procedures to avoid postoperative speech, sensory, and motordysfunction where possible.

The question addressed in this evidence review is: Does the use of MEG/MSI to map eloquent and sensorimotor brainareas accurately localize these areas and reduce postoperative functional impairment and, thus, result in changes in management and improvement in health outcomes?

The following PICO was used to select literature to inform this review.

Patients
The relevant population of interest is patients with brain lesions who are being evaluated for resective surgery.

Interventions
The intervention of interest is the use of MEG/MSI to map eloquent and sensorimotor brain areas. MEG/MSI is a noninvasive alternative to the preoperative Wada test (intracarotid sodium amobarbital procedure) used to map eloquent brain areas.

Comparators
The following test and practice are currently being used to make decisions about localization of eloquent function areas:the Wada test and other standard evaluations.

Outcomes
Outcomes of interest are diagnostic accuracy (e.g., test sensitivity and specificity) and clinical utility (e.g., consideration ofavoidance of invasive testing).

Technically Reliable
Assessment of technical reliability focuses on specific tests and operators and requires a review of unpublished and often proprietary information. Review of specific tests, operators, and unpublished data are outside the scope of this evidence review and alternative sources exist. This evidence review focuses on the clinical validity and clinical utility.

Clinically Valid
A test must detect the presence or absence of a condition, the risk of developing a condition in the future, or treatment response (beneficial or adverse).

A TEC Assessment (2003) of MEG/MSI concluded that evidence for this particular indication was insufficient todemonstrate efficacy.¹⁷ At that time, studies reviewed had relatively weak designs and small sample sizes. There are two ways to analyze the potential utility of MEG for this indication: MEG could potentially be a noninvasive substitute for the

Wada test, which is a standard method of determining hemispheric dominance for language. The Wada test requirescatheterization of the internal carotid arteries, which carries the risk of complications. The determination of languagelaterality is important to know to determine the suitability of a patient for surgery and what types of additional functionaltesting might be needed before or during surgery. If MEG provided concordant information with the Wada test, then suchinformation would be obtained in a safe, noninvasive manner.

Several studies have shown high concordance between the Wada test and MEG. In the largest study (n = 85),Papanicolaou et al. (2004) reported concordance between the MEG and Wada tests in 74 (87%) patients.¹⁸ In no cases were the tests discordant in a way that the findings were completely opposite. Discordant cases occurred mostly when theWada test indicated left dominance and MEG indicated bilateral language function. In an alternative type of analysis, when the test is being used to evaluate the absence or presence of language function in the side in which surgicaltreatment is being planned, using the Wada procedure as the criterion standard, MEG was 98% sensitive and 83% specific. Thus, if the presence of language function in the surgical site requires intraoperative mapping and/or a tailored surgical approach, use of MEG rather than Wada would have "missed" one case where such an approach would beneeded (false-negative MEG), and resulted in five cases where such an approach was unnecessary (false-positive MEG).However, it should be noted that the Wada test is not a perfect reference standard, and some discordance may reflect inaccuracy of the reference standard. In another study, Hirata et al. (2004) reported that MEG and the Wada test agreed in 19 (95%) of 20 cases.¹⁹

Section Summary: Clinically Valid
Available evidence comprises studies that correlate the results of MEG with results of the Wada test, which is analternative method for localization. Evidence has generally shown that concordance between MEG and the Wada test ishigh. However, the studies have not been replicated and their generalizability is limited.

Clinically Useful
A test is clinically useful if the use of the results informs management decisions that improve the net health outcome ofcare. The net health outcome can be improved if patients receive correct therapy, or more effective therapy, or avoidunnecessary therapy, or avoid unnecessary testing.

Direct Evidence
Direct evidence of clinical utility is provided by studies that have compared health outcomes for patients managed withand without the test. Because these are intervention studies, the preferred evidence would be from randomized controlledtrials.

One potential use of MEG would be to map the sensorimotor area of the brain to avoid such areas in the surgicalresection area. Intraoperative mapping just before resection is generally done as the reference standard. Preoperativemapping as potentially done by MEG might aid in determining the suitability of the patient for surgery or for assisting inthe planning of other invasive testing. Similar to the situation for localization of epilepsy focus, the literature is problematicin terms of evaluating the comprehensive outcomes of patients due to ascertainment and selection biases. Studies tend to be limited to correlations between MEG and intraoperative mapping. Intraoperative mapping would be performedanyway in most resection patients. Several studies evaluated in the TEC Assessment (2003) showed good to highconcordance between MEG/MSI findings and intraoperative mapping.¹⁷ A technology assessment of functional brain imaging prepared by the Ontario Ministry of Health (2006) reviewed 10 studies of MEG and invasive functional mappingand showed good to high correspondence between the two tests.²⁰ However, these studies did not demonstrate that MEGwould replace intraoperative mapping or reduce the morbidity of such mapping by allowing a more focused procedure.

Chain of Evidence
Indirect evidence on clinical utility rests on clinical validity. If the evidence is insufficient to demonstrate test performance,no inferences can be made about clinical utility.

Studies of the use of MEG in localizing the sensorimotor area provide only indirect evidence of utility. Niranjan et al. (2013) reviewed the results of 45 patients in whom MEG was used for localizing the somatosensory function.²¹ In 32 patients who underwent surgery, surgical access routes were planned to avoid regions identified as  somatosensory by MEG. All patients retained somatosensory function. It is unknown to what extent MEG provided unique information not provided byother tests. In a study by Tarapore et al. (2012), 24 patients underwent MEG, transcranial magnetic stimulation and intraoperative direct cortical stimulation to identify the motor cortex.²² MEG and navigated transcranial magnetic stimulation both identified several areas of motor function and the median distance between corresponding motor areas was 4.71 mm. When comparing MEG with direct cortical stimulation, the median distance between corresponding motorsites (12.1 mm) was greater than the distance between navigated transcranial magnetic stimulation and direct corticalstimulation (2.13 mm). This study did not determine whether MEG provided unique information that contributed to betterpatient outcomes.

Section Summary: Clinically Useful
There are no clinical trials that demonstrate the clinical utility of using MEG for localization and lateralization of eloquent and sensorimotor regions of the brain. Because MEG is a less invasive alternative to the Wada test, this evidenceindicates that it is a reasonable alternative. There is also some evidence that the correlation between MEG andintraoperative mapping of eloquent and sensorimotor regions is high but the test has not demonstrated sufficient accuracyto replace intraoperative mapping.

Summary of Evidence
For individuals who have drug-resistant epilepsy and are being evaluated for possible resective surgery who receive MEG/MSI, the evidence for MEG/MSI as an adjunct to standard clinical workup includes various types of case series.Relevant outcomes are test accuracy and clinical utility. Published evidence on MEG is suboptimal, with no clinical trials demonstrating clinical utility. The literature on diagnostic accuracy has methodologic limitations, primarily selection and ascertainment bias. Studies of functional outcomes do not fully account for the effects of MEG, because subjects whoreceived MEG were not fully accounted for in the studies. The evidence is insufficient to determine the effects of thetechnology on health outcomes.

For individuals who have a planned brain resection who require localization of eloquent function areas who receive MEG/MSI, the evidence includes comparative studies. Relevant outcomes include test accuracy and clinical utility. Available studies have reported that this test has high concordance with the Wada test, which is currently the main alternative to localize eloquent functions. While management is changed in some patients based on MEG testing, it has not been demonstrated that these changes lead to improved outcomes. The evidence is insufficient to determine theeffects of the technology on health outcomes.

Clinical Input From Physician Specialty Societies and Academic Medical Centers
While the various physician specialty societies and academic medical centers may collaborate with and make recommendations during this process, through the provision of appropriate reviewers, input received does not representan endorsement or position statement by the physician specialty societies or academic medical centers, unless otherwise noted.

In response to requests, input was received from two physician specialty societies (five reviewers) and two academic medical centers while this policy was under review in 2011. There was support for use of magnetoencephalography and magnetic source imaging for localization of language function and as part of the preoperative evaluation of intractable seizures. Those providing input indicated that use of magnetoencephalography and magnetic source imaging in the preoperative evaluation leads to the identification of additional people whose epilepsy may be cured using a surgical approach.

Practice Guidelines and Position Statements
American Clinical Magnetoencephalography Society
The American Clinical Magnetoencephalography Society (ACMS, 2009) released a position statement supporting theroutine clinical use of magnetoencephalography (MEG) plus magnetic source imaging for presurgical evaluation ofpatients with medically intractable seizures (see Rationale section).¹⁴ 

The ACMS (2011) issued a series of practice guidelines on magnetic evoked fields addressing different aspects of thistechnology (recording and analysis of spontaneous cerebral activity,²³ presurgical functional brain mapping usingmagnetic evoked fields,²⁴ MEG and electroencephalogram reporting²⁵, and qualifications of MEG-electroencephalogrampersonnel).²⁶ Methods of guideline development were not described.

Guideline 2 on presurgical functional brain mapping indicated that: 

"Magnetoencephalography shares with EEG high temporal resolution, but its chief advantage in pre-surgical functionalbrain mapping is in its high spatial resolution. Magnetic evoked fields are therefore done for localization; unlike electricalevoked potentials (EPs), [magnetic evoked fields] latencies and latency asymmetries are not typically used to detectabnormalities."²⁴ 

Proposed indications for MEG included localization of somatosensory, auditory, language and motor evoked fields.²⁴ 

The ACMS (2017) issued another position statement supporting the routine use of MEG/magnetic source imaging for obtaining noninvasive localizing or lateralizing information regarding eloquent cortices (somatosensory, motor, visual,auditory and language) in the presurgical evaluation of patients with operable lesions preparing for surgery.²⁷ 

U.S. Preventive Services Task Force Recommendations
Not applicable

Ongoing and Unpublished Clinical Trials
A search of ClinicalTrials.gov on Aug. 3, 2020, did not identify any ongoing or unpublished trials that would likelyinfluence this review. 

References:   

1. Food and Drug Administration (FDA). Devices@FDA: CTF Systems, Inc. Whole-Cortex MEG system (with optionalEEG subsystem) (K971329). 1997; https://www.accessdata.fda.gov/scripts/cdrh/devicesatfda/index.cfm?db=pmn&id=K971329. Accessed August 3, 2020.
2. Food and Drug Administration. Section 510(k) Premarket Notification K152184 MagView Biomagnetometer. 2016;https://www.accessdata.fda.gov/cdrh_docs/pdf15/k152184.pdf. Accessed August 3, 2020.
3. Blue Cross and Blue Shield Association Technology Evaluation Center (TEC). Special Report:Magnetoencephalography and magnetic source imaging for the purpose of presurgical localization of epilepticlesions--a challenge for technology evaluation. TEC Assessments. 2008;Volume 23:Tab 8.
4. Knowlton RC, Elgavish RA, Limdi N, et al. Functional imaging: I. Relative predictive value of intracranialelectroencephalography. Ann Neurol. Jul 2008; 64(1): 25-34. PMID 18412264
5. Knowlton RC, Razdan SN, Limdi N, et al. Effect of epilepsy magnetic source imaging on intracranial electrodeplacement. Ann Neurol. Jun 2009; 65(6): 716-23. PMID 19557860
6. Lau M, Yam D, Burneo JG. A systematic review on MEG and its use in the presurgical evaluation of localization-related epilepsy. Epilepsy Res. May 2008; 79(2-3): 97-104. PMID 18353615
7. Mouthaan BE, Rados M, Boon P, et al. Diagnostic accuracy of interictal source imaging in presurgical epilepsyevaluation: A systematic review from the E-PILEPSY consortium. Clin Neurophysiol. May 2019; 130(5): 845-855.PMID 30824202
8. Kim H, Kankirawatana P, Killen J, et al. Magnetic source imaging (MSI) in children with neocortical epilepsy:surgical outcome association with 3D post-resection analysis. Epilepsy Res. Sep 2013; 106(1-2): 164-72. PMID23689013
9. Schneider F, Irene Wang Z, Alexopoulos AV, et al. Magnetic source imaging and ictal SPECT in MRI-negativeneocortical epilepsies: additional value and comparison with intracranial EEG. Epilepsia. Feb 2013; 54(2): 359-69.PMID 23106128
10. Widjaja E, Shammas A, Vali R, et al. FDG-PET and magnetoencephalography in presurgical workup of childrenwith localization-related nonlesional epilepsy. Epilepsia. Apr 2013; 54(4): 691-9. PMID 23398491
11. Albert GW, Ibrahim GM, Otsubo H, et al. Magnetoencephalography-guided resection of epileptogenic foci inchildren. J Neurosurg Pediatr. Nov 2014; 14(5): 532-7. PMID 25238627
12. Wang Y, Liu B, Fu L, et al. Use of interictal (18)F-fluorodeoxyglucose (FDG)-PET and magnetoencephalography(MEG) to localize epileptogenic foci in non-lesional epilepsy in a cohort of 16 patients. J Neurol Sci. Aug 15 2015;355(1-2): 120-4. PMID 26066558
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14. Bagic A, Funke ME, Ebersole J. American Clinical MEG Society (ACMEGS) position statement: the value ofmagnetoencephalography (MEG)/magnetic source imaging (MSI) in noninvasive presurgical evaluation of patientswith medically intractable localization-related epilepsy. J Clin Neurophysiol. Aug 2009; 26(4): 290-3. PMID19602984
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17. Blue Cross and Blue Shield Association Technology Evaluation Center (TEC). Magnetoencephalography (MEG)and magnetic source imaging (MSI): presurgical localization of epileptic lesions and presurgical function mapping.TEC Assessments. 2003;Volume 18:Tab 6.
18. Papanicolaou AC, Simos PG, Castillo EM, et al. Magnetocephalography: a noninvasive alternative to the Wadaprocedure. J Neurosurg. May 2004; 100(5): 867-76. PMID 15137606
19. Hirata M, Kato A, Taniguchi M, et al. Determination of language dominance with synthetic aperture magnetometry:comparison with the Wada test. Neuroimage. Sep 2004; 23(1): 46-53. PMID 15325351　
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21. Niranjan A, Laing EJ, Laghari FJ, et al. Preoperative magnetoencephalographic sensory cortex mapping.Stereotact Funct Neurosurg. 2013; 91(5): 314-22. PMID 23797479
22. Tarapore PE, Tate MC, Findlay AM, et al. Preoperative multimodal motor mapping: a comparison ofmagnetoencephalography imaging, navigated transcranial magnetic stimulation, and direct cortical stimulation. JNeurosurg. Aug 2012; 117(2): 354-62. PMID 22702484
23. Bagic AI, Knowlton RC, Rose DF, et al. American Clinical Magnetoencephalography Society Clinical PracticeGuideline 1: recording and analysis of spontaneous cerebral activity. J Clin Neurophysiol. Aug 2011; 28(4): 348-54.PMID 21811121
24. Burgess RC, Funke ME, Bowyer SM, et al. American Clinical Magnetoencephalography Society Clinical PracticeGuideline 2: presurgical functional brain mapping using magnetic evoked fields. J Clin Neurophysiol. Aug 2011;28(4): 355-61. PMID 21811122
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26. Bagic AI, Barkley GL, Rose DF, et al. American Clinical Magnetoencephalography Society Clinical PracticeGuideline 4: qualifications of MEG-EEG personnel. J Clin Neurophysiol. Aug 2011; 28(4): 364-5. PMID 21811124
27. Bagic AI, Bowyer SM, Kirsch HE, et al. American Clinical MEG Society (ACMEGS) Position Statement #2: TheValue of Magnetoencephalography (MEG)/Magnetic Source Imaging (MSI) in Noninvasive Presurgical Mapping ofEloquent Cortices of Patients Preparing for Surgical Interventions. J Clin Neurophysiol. May 2017; 34(3): 189-195.PMID 28059855

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Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive. 

This medical policy was developed through consideration of peer-reviewed medical literature generally recognized by the relevant medical community, U.S. FDA approval status, nationally accepted standards of medical practice and accepted standards of medical practice in this community, Blue Cross Blue Shield Association technology assessment program (TEC) and other non-affiliated technology evaluation centers, reference to federal regulations, other plan medical policies and accredited national guidelines.

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