American Clinical MEG Society (ACMEGS) position statement: the value of magnetoencephalography (MEG)/magnetic source imaging (MSI) in noninvasive presurgical evaluation of patients with medically intractable localization-related epilepsy.

The American Clinical Magnetoencephalography Society (ACMEGS) is a professional society of physicians and other professionals with doctoral degrees “involved in clinical use of magnetoencephalography (MEG), electroencephalography (EEG), magnetic resonance imaging, or computerized axial tomography” (ACMEGS, Inc, Bylaws, 2006). The ACMEGS is primarily focused on advancing clinical applications of MEG, while representing all American MEG centers and individual professionals concerned with clinical MEG. Currently, our membership is composed of more than 50 individuals and/or collective members, including the most prominent investigators who have made cardinal contributions to the development of the clinical MEG. A significant proportion of 4,000 , peer-reviewed, MEDLINE publications on “MEG” has been authored by members of the American MEG community, including the most sophisticated clinical MEG studies designed and published internationally (Knowlton et al., 2008a,b; Sutherling et al., 2008). MEG/magnetic source imaging (MSI) is a modern and powerful technology for studying brain function directly and noninvasively by analyzing magnetic fields induced by synchronized neuronal activity that are recorded outside of the skull (Cohen, 1968, 1972; reviewed in Hamalainen et al., 1993; Okada et al., 1984, 1999; Williamson et al., 1991). Routinely, MEG can attain a temporal resolution of less than a millisecond and, under optimal circumstances, spatial resolution of several millimeters (Brenner et al., 1975; Hamalainen et al., 1993; Hari et al., 1988; Okada et al., 1984, 1999; Romani et al., 1982). During the last 40 years, MEG instruments have evolved from a single-channel portable system to the modern whole head systems with more than 300 channels that are housed in multilayered shielded rooms (reviewed in Barkley and Baumgartner, 2003; reviewed in Hamalainen et al., 1993). It is now accepted that MEG/MSI can provide clinicians with accurate and critical information regarding the location of important cerebral sources, such as epileptic foci (Baumgartner, 2000; Ebersole, 1997; Fischer et al., 2005; Iwasaki et al., 2002; Kirsch et al., 2007a; Knake et al., 2006; Knowlton, 2006, 2008; Knowlton et al., 2006; Knowlton et al., 2008a,b; Lin et al., 2003; Mamelak et al., 2002; Mohamed et al., 2007; Oishi et al., 2006; Papanicolaou et al., 2005; Pataraia et al., 2004; RamachandranNair et al., 2007; Rodin et al., 2004; Smith et al., 2000; Stefan et al., 2003; Sutherling et al., 2008; Verrotti et al., 2003), sensory-motor cortex (Alberstone et al., 2000; Brenner et al., 1975; Castillo et al., 2004; Ganslandt et al., 2004; Kirsch et al., 2007b; Korvenoja et al., 2006; Nakasato and Yoshimoto, 2000; Oishi et al., 2003; Okada et al., 1984; Pang et al., 2008), visual (Alberstone et al., 2000; Brenner et al., 1975; Ganslandt et al., 2004; Grover et al., 2006; Nakasato and Yoshimoto, 2000; Nakasato et al., 1996), auditory (Alberstone et al., 2000; Godey et al., 2001; Nakasato and Yoshimoto, 2000; Romani et al., 1982), and language cortex (Bowyer et al., 2004, 2005; Flagg et al., 2005; Ganslandt et al., 2004; Grummich et al., 2006; Hirata et al., 2004; Kamada et al., 2003; Lee et al., 2006; Merrifield et al., 2007; Papanicolaou et al., 2004, 2006; Salmelin, 2007) MEG/MSI findings may be displayed on a patient’s magnetic resonance imaging or combined with other imaging modalities to form multimodal neuronavigational maps that can be used directly in stereotactic neuronavigation systems during surgery (Duffner et al., 2003; Firsching et al., 2002; Ganslandt et al., 1999; Kamada et al., 2003, 2007; Nimsky et al., 1999; Ochi and Otsubo, 2008; Rezai et al., 1995, 1996, 1997). Nearly 3 million Americans are afflicted with epilepsy (Hauser and Hesdorffer, 1990). Approximately 30% suffer from seizures that are refractory to medications despite the 20 antiepileptic drugs that are currently available (Brodie, 2005; Kwan and Brodie, 2000). These patients are responsible for 80% of the $12.5 billon annual cost of epilepsy to society (Begley et al., 2000). A significant minority of these patients with epilepsy have localization-related or focal epilepsy that may be amenable to surgical therapy (Engel, 2003, 2008). Thus, competent estimates indicate that 100,000 to 200,000 patients with uncontrolled epilepsy may be surgical candidates (Engel, 2003; Engel and Shewmon, 1993). Epilepsy surgery has been proven to be superior to medical treatment in patients with temporal lobe epilepsy in a randomized controlled trial (Engel, 2008; Engel et al., 2003; Wiebe et al., 2001), and a recent analysis revealed that “the combination of surgery with medical treatment is four times as likely as medical treatment alone to achieve freedom from seizures” (Schmidt and Stavem, In press). Furthermore, long-term follow-up studies showed that many patients who underwent resective brain surgery remain seizure free (Spencer and Huh, 2008; Tellez-Zenteno et al., 2005, 2007, 2008) and that “in carefully selected patients, epilepsy surgery can control seizures, improve quality of life, and reduce costs of medical care” (Kuzniecky and Devinsky, 2007). However, for multiple reasons, epilepsy surgery, the only potential cure for epilepsy (Engel, 2003, 2008; Spencer and Huh, 2008; Wiebe et al., 2001), is offered to only 2% to 3% of potential surgical candidates (Engel, 2003). The critical and often rate-limiting factor in epilepsy surgery is functional localization of the epileptic focus that may not be adequately supplied by traditional diagnostic investigations, including EEG, video-EEG monitoring, magnetic resonance imaging, and in some cases positron emission tomography (PET) and singlephoton emission computed tomography (SPECT) scans (Barkley From the *Center for Advanced Brain Magnetic Source Imaging (CABMSI), Departments of Neurology & Neurosurgery, The University of Pittsburgh, Pittsburgh, PA; †Magnetic Source Imaging, Department of Neurology, Clinical Neurosciences Center, The University of Utah, Salt Lake City, UT; and the Department of Neurology, The University of Chicago, Chicago, IL. ISSN: 0736-0258/09/2604-0001