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DESCRIPTIONMagnetoencephalography (MEG) is a noninvasive functional imaging technique in which weak magnetic forces are recorded externally. When this information is superimposed on an anatomic image of the brain, typically an MRI scan, the image is referred to as magnetic source imaging (MSI). This technique has been studied for identifying “eloquent” areas of the brain for neurosurgical planning and for use in localization of epileptic foci.
MEG is a noninvasive functional imaging technique in which the weak magnetic forces associated with the electrical activity of the brain are recorded externally on the scalp. Using mathematical modeling, the recorded data are then analyzed to provide an estimated location of the electrical activity. This information can be superimposed on an anatomic image of the brain, typically a MRI, to produce a functional/anatomic image of the brain, referred to as magnetic source imaging or MSI. The primary advantage of MSI is that while the conductivity and thus measurement of electrical activity as recorded by the EEG is altered by surrounding brain structures, the magnetic fields are not. Therefore, MSI permits a high-resolution image.
The technique itself is extremely sophisticated. Detection of the weak magnetic fields depends on gradiometer detection coils coupled to SQUIDs (superconducting quantum interference device), which in turn require a specialized room, shielded from other magnetic sources. Mathematical modeling programs based on idealized assumptions are then used to translate the 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, were also difficult to coordinate with the MRI. However, more recently the technique has evolved to 37 or more detection coils arranged in an array that can provide data more efficiently over a wide extracranial region.
The most thoroughly studied clinical application is localization of the pre- and post-central gyri as a guide to surgical planning in those patients scheduled to undergo neurosurgery for epilepsy, brain neoplasms, arteriovenous malformations, or other brain disorders. 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 the anatomy is distorted by underlying disease process. In addition, the location of the eloquent functions is variable even among normal patients. Therefore, localization of the eloquent cortex often requires such intraoperative invasive functional techniques as cortical stimulation under local anesthesia or somatosensory evoked responses on electrocorticography (EcoG). While 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. Futhermore, sometimes these techniques can 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.
Another related clinical application is localization of epileptic foci, particularly for screening of surgical candidates and surgical planning. Alternative techniques include MRI, PET, or SPECT scanning. Anatomic imaging (i.e., MRI) is effective when epilepsy is associated with a mass lesion, such as a tumor, vascular malformations, or hippocampal atrophy. If an anatomic abnormality is not detected, patients may undergo a PET scan. In a small subset of patients, extended electrocorticography (EcoG) or stereotatic electroencephalography EEG (SEEG) with implanted electrodes is considered the gold standards for localizing epileptogenic foci. MEG/MSI has principally been investigated as an alternative to invasive monitoring.
POLICYMagnetoencephalography/ 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 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 considered investigational for all other indications.
POLICY EXCEPTIONSFederal Employee Program (FEP) may dictate that all FDA-approved devices, drugs or biologics may not be considered investigational and thus these devices may be assessed only on the basis of their medical necessity.
POLICY GUIDELINESInvestigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY2/2000: Approved by Medical Policy Advisory Committee (MPAC)
2/11/2002: Investigational definition added
2/21/2002: Code Reference section completed, CPT code 95965, 95966, 95967 added
5/1/2002: Type of Service and Place of Service deleted
8/15/2005: Code Reference section updated, CPT code 95965, 95966, 95967 description revised
10/23/2006: Policy reviewed, no changes
1/7/2009: Policy reviewed, medically necessary application listed
2/4/2009: Policy statement updated to indications which are now medically necessary. Code section update.
04/22/2010: “Magnetic Source Imaging” added to the policy title. Policy description updated. Added language to the policy statements to clarify that they apply to MEG and MSI. HCPCS code S8035 was previously added to codes table. FEP verbiage added to the Policy Exceptions section. Deleted outdated references from the Sources section.
04/20/2011: Policy reviewed; no changes.
11/30/2012: Policy statement revised to state that magnetoencephalography/magnetic source imaging as 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).
12/13/2013: Policy reviewed; no changes.
SOURCE(S)Blue Cross Blue Shield Association policy #6.01.21
CODE REFERENCEThis may not be a comprehensive list of procedure codes applicable to this policy.
The code(s) listed below are ONLY medically necessary if the procedure is performed according to the "Policy" section of this document.