Magnetic Resonance Angiography (MRA)

1. Aetna considers magnetic resonance angiography (MRA) to be medically necessary according to the selection criteria outlined below. MRA is considered appropriate when it can replace a more invasive test (e.g., contrast angiography) and reduce risk for members. While MRA is a rapidly evolving technology, its clinical safety and effectiveness for all anatomical regions have not been established by the peer reviewed medical literature.

   Head and Neck

   MRA of the head and neck is considered medically necessary for any of the following conditions:

   1. To rule out intracranial aneurysm (ICA), including aneurysms of the circle of Willis, in members who are thought to be at higher risk (e.g., history of ICA in a first-degree relative or presence of polycystic kidney disease); or
   2. To evaluate pulsatile tinnitus in members with signs or symptoms suggestive of a vascular lesion; or
   3. As a follow-up study for a known arteriovenous malformation (AVM), and for a known non-ruptured intracranial aneurysm that is greater than 3 mm in size; or
   4. To evaluate members with signs/symptoms highly suggestive of leaking/ruptured ICA or AVM (i.e., sudden explosive headache, stiff neck, blood in the cerebral spinal fluid); or
   5. To definitively establish presence of stenoses or other abnormalities of the vertebrobasilar system in members with symptoms highly suggestive of vertebrobasilar syndrome (binocular vision loss, positional vertigo, dysarthria, dysphagia, diplopia); or

   6. To evaluate conditions of the carotid arteries such as:

      1. Stenotic / occlusive disease in symptomatic members (e.g., TIA or CVA)
      2. Stenotic / occlusive disease in asymptomatic members who are candidates for carotid endarterectomy surgery (CEA) when a Duplex Doppler Scan is abnormal
      3. Aneurysm Tumor
      4. Cervicocranial arterial dissection in members with suggestive signs or symptoms (e.g., unilateral headache, oculosympathetic palsy, amaurosis fugax, and symptoms of focal brain ischemia)

      5. Injury to the carotid artery.

   Note: As MRA is considered an alternative to angiography for evaluation of the carotids, a subsequent angiography would only be considered medically necessary if there was a significant discrepancy between the findings of Duplex ultrasonography and MRA that would impact on surgical planning.

   Chest

   MRA of the chest is considered medically necessary for any of the following indications:

   1. For diagnosis, treatment planning, and post-operative follow-up for conditions of the thoracic aorta such as aneurysm (true or pseudoaneurysm), dissection, or stenotic / occlusive vascular disease; or
   2. For diagnosis, treatment planning, and post-operative surgical shunt evaluation in members with congenital heart disease (CHD) or developmental anomalies of the thoracic vasculature (e.g., coarctation of the aorta, right-sided aortic arch, double aortic arch, truncus arteriosus, persistent left superior vena cava, interrupted inferior vena cava, total anomalous pulmonary venous connection, partial anomalous venous connection, atresia or hypoplasia of the pulmonary arteries); or

   3. For diagnosing a suspected pulmonary embolism when the use of intravascular iodinated contrast material is contraindicated, or as a substitute for pulmonary angiography when a ventilation/perfusion (VQ) scan does not provide sufficient information for treatment decisions.

   Abdomen

   MRA of the abdomen is considered medically necessary for any of the following indications:

   1. To assess of the main renal arteries for the evaluation of renal artery stenosis in persons with refractory uncontrolled hypertension* not due to pheochromocytoma; or
   2. To assess pelvic (e.g., aortoiliac) arteries for stenoses in members with peripheral vascular disease; or
   3. To determine the extent of an abdominal aortic aneurysm and associated occlusive disease in members undergoing elective repair; or
   4. To evaluate for chronic mesenteric ischemia.

      * Refractory hypertension is defined as diastolic blood pressure consistently greater than 100 mm Hg on three or more blood pressure medications.

   Lower Extremity

   MRA of the lower extremities is considered medically necessary as an initial test for diagnosis and surgical planning in the treatment of peripheral arterial disease of the lower extremity. A subsequent angiography study is only required if the inflow vessel is not identified on the MRA. If conventional catheter angiography is performed first, doing a subsequent MRA may be indicated if a distal run off vessel is not identified. Both tests should not be routinely performed.

   Allergy, etc.

   The use of MRA is considered medically necessary in members with documented allergy to iodinated contrast material, and in members who have accelerating hypertension and/or accelerating renal insufficiency.

2. Aetna considers MRA to be experimental and investigational for all other indications, including any of the following:
   
   
   1. Screening of the general population for intracranial aneurysms; or
   2. To rule out intracranial aneurysms in members who have vague CNS symptoms (e.g., non-specific sensory loss, dizziness, vertigo, or headache); or
   3. To evaluate members with symptoms suggestive of dural, sagittal or cavernous sinus thrombosis / occlusion; or
   4. As a screening method for renovascular hypertension; or
   5. For evaluation of accessory renal arteries in prospective renal donors, including potential living kidney donors; or

   6. Cardiac MRI for velocity flow mapping.

Magnetic Resonance Venography (MRV)

1. Aetna considers MRV to be medically necessary for any of the following indications:

   1. For evaluation of thrombosis or compression by tumor of the cerebral venous sinus in members who are at risk (e.g., otitis media, meningitis, sinusitis, oral contraceptive use, underlying malignant process, hypercoagulable disorders) or have signs or symptoms (e.g., papilledema, focal motor or sensory deficits, seizures, or drowsiness and confusion accompanying a headache); or
   2. For evaluation of venous thrombosis or occlusion in the large systemic veins (e.g., superior vena cava, subclavian, or other deep veins in the chest); or

   3. For evaluation of venous thrombosis or occlusion in the portal and/or hepatic venous system (e.g., Budd-Chiari syndrome).

2. Aetna considers MRV to be experimental and investigational for diagnosis of deep vein thrombosis in the arms or legs because the peer reviewed medical literature has not established MRV to be superior to Duplex ultrasonography for this purpose. MRV is considered experimental and investigational for all other indications.

Magnetic resonance angiography (MRA) is an application of magnetic resonance imaging (MRI) that provides visualization of blood flow, as well as images of normal and diseased blood vessels. While MRA appears to be a rapidly developing technology, the clinical safety and effectiveness of this procedure for all anatomical regions has not been proven.

The use of MRA in evaluating flow in the carotid arteries, the circle of Willis, the anterior, middle or posterior cerebral arteries, the vertebral or basilar arteries, or the venous sinuses have been the most well researched applications. Numerous articles have demonstrated that MRA can image the vessels with a high degree of sensitivity and specificity. However, the appropriate use of MRA in this setting must be coordinated with the use of the competing technologies, Duplex ultrasonography and angiography. There is no mention in the literature that all three technologies should be used routinely in the work up of carotid artery disease. In terms of screening patients with symptoms suggestive of disease, duplex ultrasonography has been shown to be equivalent to MRA, and thus this test is recommended as the initial diagnostic test. In terms of surgical planning, MRA has been shown to be competitive with angiography, therefore this test can be the second definitive test used for surgical planning. In this scenario, an angiography would only be considered medically necessary if the ultrasonography and MRA showed major discrepancies. Finally, in a more limited role, MRA has been suggested as an alternative to angiography in those patients unable to undergo an angiogram due to allergy to contrast material.

Patients with transient ischemic attacks or strokes typically undergo MRI as part of the initial work up to identify infarcted areas in the brain. An intracranial MRA can be easily appended to the MRI and for that reason has been frequently ordered. However, an intracranial MRA is considered not medically necessary. MRI can adequately image any infarcted areas, and in the case of transient ischemic attacks, by definition, one would not expect to see any vascular abnormalities. The use of MRA in the work up of patients with the vertebrobasilar syndrome must be considered on a case-by-case basis. The MRA may be appropriate in patients when other sources of emboli have been ruled out, and the MRA is considered as an alternative to an angiogram in order to establish the diagnosis of vertebral artery disease.

Although MRA provides additional imaging capabilities for intracranial aneurysms and vascular lesions, it is not clear from the literature how this information will impact on patient management. In particular, patients who present subacutely with symptoms consistent with aneurysm or vascular malformations will probably undergo a conventional spin-echo MRI followed by angiography, if indicated. It is unclear from the literature how MRA would alter this imaging hierarchy. Several authors commented that the anatomic detail provided by MRA is not sufficient to replace an angiogram. MRA has also been suggested as a novel screening technique for patients at high risk for aneurysm; however, its clinical relevance is unknown because of a lack of understanding of the natural history of aneurysms and which aneurysms represent a high risk of rupture. Due to its low diagnostic yield, MRA is considered not medically necessary for the routine work up of patients with non-specific, non-focal symptoms, such as headache or dizziness.

MRA is an effective noninvasive technique for establishing a diagnosis and evaluating the extent and severity of nearly all diseases of the thoracic aorta. Studies have shown that MRA of the chest has a high level of diagnostic accuracy for pre-operative and post-operative evaluation of aortic dissection of aneurysm. Depending on the clinical presentation, MRA may be used as an alternative to other non-invasive imaging technologies, such as transesophageal echocardiography and CT.

Current scientific data shows that diagnostic pulmonary MRAs are improving due to recent developments such as faster imaging capabilities and gadolinium-enhancement. However, these advances in MRA are not significant enough to warrant replacement of pulmonary angiography in the diagnosis of pulmonary embolism for patients who have no contraindication to receiving intravenous iodinated contrast material. The tortuous pulsatile nature of the coronary arteries presents an imposing technical challenge to MRA. The application of MRA for this purpose is still in its infancy.

Studies have proven that MRA is considered a reliable diagnostic tool for the pre-operative evaluation of patients who will undergo elective abdominal aortic aneurysm (AAA) repair. In addition, scientific data has revealed that MRA is considered comparable to conventional angiography in determining the extent of the AAA, as well as evaluation of aortoilliac occlusion disease and renal artery pathology that may be necessary in the surgical planning for AAA repair. If preoperative angiography is not necessary, then patients are not exposed to the risks associated with invasive contrast procedures, namely allergic reactions, end-organ damage or arterial injury. MRA has also become accepted as a method to detect suspected stenosis in the main renal arteries; its inability to image distal lesions and accessory arteries limits its diagnostic abilities.

Although MRA assessment for the evaluation of renal artery stenosis is acceptable, the accuracy of MRA as a screening method for renovascular hypertension is unproven, and MRA is inadequate in the identification of accessory renal arteries because it has not achieved the level of accuracy needed to replace conventional angiography in the evaluation of potential living renal donors.

Surgical planning for peripheral arterial occlusive disease in the lower extremities depends on identification of adequate inflow and distal run off vessels. MRA has been shown to be a superior technique in identifying distal run off vessels and is competitive with angiography in identifying appropriate inflow vessels. Therefore, MRA can be used as an initial test for surgical planning, with a subsequent angiography only if the inflow vessel is not identified. If angiography is performed first, an MRA may be appropriate if a distal run off vessel is not identified because MRA is capable of detecting a viable run-off vessel for bypass not seen on traditional angiography, especially when exploratory surgery is not believed to be a reasonable medical course of action for the patient.

The use of an MRA/MRV as part of the work up of a patient with suspected cerebral thrombosis (i.e., dural sagittal or cavernous sinus thrombosis) must be considered on a case by case basis. MRI is considered the imaging method of choice for establishing the diagnosis, but MRA/MRV may be useful in following the course of the disease.

Magnetic resonance venography (MRV) is now very effective for the evaluation of diseases of larger veins. The specific indications for using MRV for evaluating the vena cavae are diagnosis of vena caval thrombus, differentiation of tumor thrombus and blood clot of the vena cava, diagnosis of superior vena caval syndrome, identification of superior vena caval invasion or encasement by lung or mediastinal tumors, diagnosis of the Budd-Chiari syndrome, diagnosis of caval anomalies such as persistent left superior vena cava and interrupted inferior vena cava, and identification of the presence and cause of obstruction or occlusion of the brachiocephalic, subclavian, and jugular veins.

Duplex ultrasonography is the typical initial diagnostic test for deep vein thrombosis (DVT). Magnetic resonance venography has not been shown to be superior to ultrasonography, except in imaging the deep femoral and hypogastric vessels. However, information about these vessels is frequently not needed to make patient management decisions, except perhaps in patients with pulmonary emboli where the source of the emboli has not been identified by ultrasonography. McRae and Ginsberg (2004) MRV has the potential to be used as a stand-alone test for DVT but requires further evaluation. Moreover, in a retrospective study (n = 973), Borer, et al. (2005) found that discontinuation of screening by means of ultrasound and MRV for the diagnosis of DVT did not change the rate of pulmonary embolism in patients with closed fractures of the pelvis or acetabulum.