American Clinical MEG Society (ACMEGS) Position Statement #2: The Value of Magnetoencephalography (MEG)/Magnetic Source Imaging (MSI) in Noninvasive Presurgical Mapping of Eloquent Cortices of Patients Preparing for Surgical Interventions

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The American Clinical Magnetoencephalography Society (ACMEGS) is a professional society of physicians and other professionals with doctoral degrees involved in all aspects of magnetoencephalography (MEG), including simultaneously collected EEG and coregistration of localization results to MRI.1 The ACMEGS is primarily focused on advancing clinical applications of MEG, while representing all American MEG centers and individual professionals concerned with clinical MEG. To this extent, the ACMEGS published its first Position Statement in 20092: “The Value of Magnetoencephalography (MEG)/Magnetic Source Imaging (MSI) in Noninvasive Presurgical Evaluation of Patients With Medically Intractable Localization-related Epilepsy.” This document has been referenced in more than a dozen positive coverage policies of private insurers in the United States of America such as AETNA,3 blue cross of Idaho,4 blue cross blue shield of Alabama5 and Illinois,6 blue shield of California,7 Cigna Medical Coverage Policy,8 Healthnet National Policy9; Oxford Health Plan,10 Highmark Medical Policy,11 Independence,12 United Healthcare,13 and more can be found here ( The document has been also referenced in more than 10 peer-reviewed publications.14–16In addition to position statements, the ACMEGS has engaged in sustained systematic efforts to improve and standardize clinical practice of MEG. These efforts have resulted in publication of the world's first clinical practice guidelines (CPGs) for MEG in 2011,17–20 which were endorsed by the American Clinical Neurophysiology Society (ACNS).21 The guidelines have received increasing national and international acceptance not only by clinicians22–26 but also by insurers.27 Currently, our membership represents the majority of American MEG centers with an active clinical program (i.e., “institutional members”) and individuals, including the most prominent investigators who have made cardinal contributions to the development of clinical MEG. A significant proportion of more than 7,400 (nearly 2,500 over the last 5 years; accessed on January 18, 2016), peer-reviewed, MEDLINE publications on “magnetoencephalography” have been authored by members of the American MEG community, including the most relevant clinical MEG studies28–32 published internationally (e.g., reviewed in Refs. 2,33–36).Traditionally, the “gold standard” for determination of the exact location of cardinal neurosurgical landmarks such as central sulcus and delineation of language, motor, or other eloquent cortices has been direct cortical stimulation mapping37–40 and for lateralization of the language cortex has been the Wada or intracarotid amobarbital procedure.41–45 However, cortical stimulation mapping increases intraoperative time and risks after-dischages or if extraoperative, requires the implantation of chronic electrodes with its attendant risks. Intracarotid amobarbital procedure is associated with the risk of noteworthy complications in 6%46 to 11% of patients.47 These invasive techniques have other significant drawbacks: reliance on sufficient patient cooperation, discomfort, some specific functional limitations, limited or no repeatability, and some ambiguity and complexity of logistics.35 For instance, intracarotid amobarbital procedure requires a team of several professionals working in the angiography suite for a few hours and involves an invasive intravascular procedure that exposes the patients to various risks such as infection, stroke, or bleeding.42–46 Because the invasive methods rely on interruption of function while MEG evaluates activation, the legitimacy of these invasive gold standards has been questioned,35 including their validity48,49 and positive predictive value of favorable outcome.50 While noninvasive methods (MEG, functional MRI [fMRI], positron emission tomography (PET), and transcranial magnetic stimulation) have their inherent differences as well as functional and/or logistical limitations (e.g., bilateral and/or multiregional activation, a necessity to determine a specific “threshold” of activation, patient cooperation), they also possess clear advantages: noninvasive, repeatable, and customizable.35,51–55Magnetoencephalography is an established, noninvasive, direct, and painless procedure that relies on no external magnetic fields, electricity, x-rays, or radioactivity.

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