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Functional magnetic resonance imaging (fMRI) is a noninvasive method for evaluation of eloquent brain areas. Images are collected while specific activities are performed to assist in the presurrgical localization of critical cortical areas and evaluation of language lateralization. fMRI is also being investigated in combination with diffusion tensor imaging, which measures white matter tract organization, and electroencephalogram (fMRI-EEG) to identify seizure focus.
Before neurological surgery for seizure disorders or resection of brain tumors, localization of certain areas of the brain, such as speech centers, is important. For example, from 25% to 60% of patients who undergo left anterior temporal lobectomy develop dysnomia (language/naming difficulties). Most often these “eloquent” areas are assessed using the Wada test and direct electrical simulation. Both of these tests are invasive and require involvement of various specialists. Direct intracortical electrical stimulation involves functional mapping of the exposed cortex with electrodes, which may elicit a motor or verbal response including arrest of speech, random answering, or perseveration to stimulation. The Wada test is an inactivating method that blocks the function of one hemisphere by injection of amobarbital into the carotid artery, allowing functional testing of the reserve capacity of the nonanesthetized hemisphere.
Functional MRI is an activation method that uses sequences based on T2-weighted blood oxygen level-dependent (BOLD) response. These studies are often done on MR scanners with field strengths of 1.5 Tesla or greater. The interhemispheric difference between activated volumes in the left and right hemispheric regions of interest is calculated as the laterality index (LI), which ranges from -1 to 1. A positive laterality index is considered left-dominant, while a negative laterality index is right dominant. Functional MRI-determined laterality indices may be derived for several different functional areas (regions of interest) that include either Broca’s area (language production) or Wernicke’s area (language comprehension). Various thresholds (e.g., -0.1 to +0.1, or -0.5 to +0.5) have been proposed to differentiate laterality from bilaterality. Bilateral activation patterns can result from the detection of language-associated, but not language-essential cortex. Therefore, bilateral activation is not necessarily indicative of a bilateral distribution of language-essential cortex and may be task dependent. In addition, sensitivity and specificity may change with the application of different statistical thresholds.
POLICYFunctional MRI may be considered medically necessary as a complementary test in the preoperative evaluation of patients with refractory epilepsy or brain tumors who are candidates for neurosurgery when the lesion is in close proximity to an eloquent area of the brain (e.g., controlling verbal or motor fuction) and testing is expected to have an important role in assessing the spatial relationship between the lesion and eloquent brain area.
Functional MRI is considered investigational for all other applications.
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 HISTORY12/21/2006: Policy added
3/22/2007: Reviewed and approved by the Medical Policy Advisory Committee (MPAC)
6/19/2009: Policy reviewed, policy statement re-written for clarity
07/09/2010: Policy description updated regarding use of functional MRI. Added "as a complementary test" to the policy statement; intent unchanged. FEP verbiage added to the Policy Exceptions section.
08/02/2011: Policy reviewed; no changes.
07/17/2012: Policy reviewed; no changes.
10/17/2013: Policy reviewed; no changes.
07/31/2014: Policy reviewed; description updated regarding direct intracortical electrical stimulation and the Wada test. Medically necessary policy statement revised to change "is considered" to "may be considered."
SOURCE(S)Blue Cross Blue Shield Association Policy # 6.01.47
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.