ARCHIVED

Medical Policy

Policy Num:       06.001.023
Policy Name:     Magnetic Resonance Angiography of Vessels of the Head, Neck, Abdomen, Pelvis, and Lower Extremity
Policy ID:          [06.001.023]   [Ar/ B / M+ / P+ ]   [6.01.16]

ARCHIVED

Last Review:     July 19, 2022
Next Review:     Archived
Issue:                 7:2022

Related Policies:

06.001.004 Magnetic Resonance Angiography of Thorax and abdomen

Magnetic Resonance Angiography of Vessels of the Head, Neck,
Abdomen, Pelvis, and Lower Extremity

Summary

Magnetic resonance angiography (MRA) is a technique for imaging vascular anatomy and pathology that does not use ionizing radiation. MRA is performed using magnetic resonance imaging (MRI) machines, and vascular images may be generated either with or without intravenous contrast agents, depending on the clinical application. However, the contrast agents used for MRA are associated with less risk of allergic reaction or nephrotoxicity than those used for conventional angiography.

Objective

MRA is the general term used to describe MR imaging of vascular structures, but when MR is used to image a vein instead of an artery, the term “magnetic resonance venography” (MRV) may be used. The technical capabilities of current MRA make it most suitable for evaluation of medium-to-large size vessels. In the head, this
includes the Circle of Willis and major posterior circulation vessels, while in the body this includes the aorta and its major arterial branches such as carotid, renal, hepatic and mesenteric arteries. MRA is less suitable for providing detailed information about the small, peripheral vasculature.

Policy Statements

MRA of the head may be considered medically necessary for the assessment of:
ï‚· patients suspected of having steno-occlusive disease of the mid or large size intracranial arteries;
ï‚· patients suspected of having cerebral aneurysm;
ï‚· patients suspected of having intracranial vascular malformation;
ï‚· patients suspected of having cerebral venous sinus compression or thrombosis;
ï‚· patients with pulsatile tinnitus;

MRA of the neck may be considered medically necessary for the assessment of:
ï‚· patients suspected of having carotid stenosis or occlusion;
ï‚· patients suspected of having cervicocranial arterial dissection.

MRA of the abdomen/pelvis may be considered medically necessary for the assessment of patients with the following clinical indications in whom angiography would otherwise be indicated and in whom a negative MRA would obviate the need for angiography:
ï‚· patients suspected of having atherosclerotic renal artery stenosis;
ï‚· patients with suspected chronic mesenteric ischemia;
ï‚· patients with abdominal aortic aneurysm who are to undergo elective repair of the aneurysm;
ï‚· patients requiring evaluation of the portal and/or hepatic venous system; patients requiring evaluation of the systemic venous system.

MRA of the pelvis/lower extremities may be considered medically necessary for the assessment of patients with the following clinical indications:
ï‚· patients with suspected atherosclerotic disease of the lower extremity in whom angiography would otherwise be indicated and in whom MRA would obviate the need for angiography;
ï‚· patients with known atherosclerotic disease of the lower extremity who are being evaluated for bypass surgery and in whom angiography fails to identify runoff vessels suitable for bypass.

MRA may be considered medically necessary in the evaluation of potential renal donors for the presence of accessory renal arteries.

Policy Guidelines

Head

Invasive cerebral angiography has been traditionally considered the reference standard to which the performance of noninvasive diagnostic tests is compared. Both magnetic resonance angiography (MRA) and transcranial Doppler ultrasonography (TCD) have been shown to be effective noninvasive diagnostic tests for evaluating patients suspected of having intracranial arterial steno-occlusive disease and may be used by some physicians as a replacement for invasive cerebral angiography. In some circumstances, either MRA or TCD alone may provide adequate information to guide appropriate management; however, there are other circumstances whereby it may be necessary to obtain both noninvasive tests before management decisions can be made. For example, the initial noninvasive study may be technically limited by patient motion (particularly a problem for MRA) or by the patient having an inadequate acoustic window (a problem unique to TCD). When this is the case, diagnostic information may be sought using the alternative noninvasive imaging tool. Furthermore, the results of the initial noninvasive evaluation may be borderline or equivocal. Since CDUS and MRA use different physical and
technical principles for evaluating the cerebral vasculature, the information obtained from each test can be complementary rather than duplicative in some circumstances.
 

Neck
Invasive angiography of the cervical carotid arteries has been used traditionally as the definitive preoperative diagnostic evaluation in patients with carotid artery bifurcation stenosis who are being considered for carotid endarterectomy (CEA). However, as recent improvements have been made in noninvasive diagnostic tests to evaluate the carotid bifurcation region, some physicians have favored a preoperative diagnostic approach using noninvasive imaging tests such as carotid duplex ultrasonography (CDUS) and/or MRA to guide management decisions.

CDUS is most commonly used as the initial noninvasive evaluation of the carotid bifurcation as it is less expensive than MRA and generally more readily available than MRA. When the clinical suspicion for steno-occlusive disease is considered along with the results of the initial test (usually CDUS), the physician can decide whether there is sufficient information to determine subsequent management for the patient or whether additional imaging is necessary. One imaging strategy that has emerged and that is supported in the available evidence, uses both CDUS and MRA to evaluate patients prior to CEA. When both noninvasive tests agree as to the necessity of CEA, the surgical management decision is made based on noninvasive imaging alone. However, if there is discordance in the results of MRA and CDUS (e.g., 1 test suggests a severe carotid stenosis but the other test suggests only a mild-to-moderate degree of stenosis), then invasive angiography is performed to determine the management decision. Using this combination strategy, the utilization of invasive angiography for preoperative evaluation for CEA has been reported to decrease substantially.

Abdomen
A variety of abdominal vascular conditions have been proposed for evaluation with contrast-enhanced MRA. Patients who are suspected of having renal artery stenosis may benefit when MRA is used to rule out significant stenosis, thus sparing the patient from invasive angiography. Patients with positive results on MRA may require confirmatory angiography before receiving surgical or intravascular stent treatment for renal artery stenosis. However, confirmation may often be performed during the catheterization for the therapeutic procedure. Similarly, patients with suspected chronic mesenteric ischemia or suspected hepatic arterial disease may benefit from the use of MRA. Potential living renal donors may benefit by using contrast-enhanced MRA for preoperative evaluation of renal anatomy as an alternative to invasive digital subtraction angiography and or computed tomographic angiography (CTA), both of which require ionizing radiation and potentially nephrotoxic iodinated intravenous contrast agents. Patients who are to undergo elective repair of an abdominal aortic aneurysm undergo preoperative angiographic evaluation to delineate the size and location of the aneurysm as well as its relationship with
renal and other branch arteries. MRA has been proposed as a replacement for invasive angiography in this situation. Similarly, patients who are to undergo abdominal organ transplantation may require presurgical angiography and may benefit from the use of MRA. CTA is also proposed as a noninvasive alternative, though CT uses iodinated contrast agents that pose a higher risk for allergic and nephrotoxic reactions. Patients with suspected abdominal or pelvic venous thrombo-occlusive disease may benefit by
using MRA to obviate the need for invasive venography.

Pelvis
Pelvic arteriography or venography may be useful in several situations to avoid the need for invasive angiography. Patients with suspected aorto-iliac atherosclerotic disease may benefit by the use of MRA to avoid the need for invasive angiography, and this evaluation often includes arterial evaluation of the lower extremities as well in patients with suspected peripheral vascular disease (e.g., claudication). Other uses of pelvic MRA would include evaluation of renal arteries with ectopic pelvic location of the kidney and
evaluation of pelvic veins for thrombo-occlusive disease.

Lower Extremity
MRA may be useful for evaluating the arterial and venous structures of the lower extremity. In patients with suspected peripheral vascular disease, MRA may be able to evaluate the extent of disease and guide therapeutic decision making without the need for invasive angiography. Furthermore, MRA may be more sensitive than conventional angiography in identifying distal runoff vessels in potential candidates for peripheral bypass surgery.

Benefit Application

BlueCard/National Account Issues

No applicable information.

Background

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 3 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.

Regulatory Status

MRI scanners are both radiation-emitting electronic products and medical devices subject to the requirements of the Food, Drug, and Cosmetic Act.

Rationale

Population Referance No. 1

Patients suspected of having steno-occlusive disease of the mid or large size intracranial arteries

MRA  with diffusion-weighted imaging (DWI) is superior to noncontrast CT for the very early detection of acute ischemia and the exclusion of some stroke mimics. In addition, MRI reliably detects hyperacute hemorrhage with sequences that include high susceptibility images such as gradient echo (GRE). However, MRI is not readily available at most centers for the acute evaluation of patients with stroke. Also, MRI in practice is more limited by patient contraindications or intolerance than CT. In one study, more than 93 percent of patients were eligible for contrast-enhanced CT compared with only 58 percent for MRI

A few reports have demonstrated that it is possible to use MRI routinely as the sole neuroimaging screening method prior to intravenous thrombolytic therapy [6,7]. In one such study of 135 patients screened with MRI and treated with intravenous alteplase (tPA), quality improvement processes led to reduced door-to-needle times of ≤60 minutes [6]. Thus, MRI can be used as the only imaging method in select centers with sufficient MRI availability for the evaluation of suspected stroke patients who do not have MRI contraindications. However, there are no data to show that MRI is superior to CT for selecting patients who could be treated with intravenous thrombolysis. Thus, MRI should be used rather than CT only if it does not unduly delay treatment with intravenous alteplase.

Brain magnetic resonance imaging (MRI) protocols that combine conventional T1 and T2 sequences with diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI), and gradient echo (GRE) can reliably diagnose both acute ischemic stroke and acute hemorrhagic stroke in emergency settings. A major advantage of MRI is that the DWI sequence is much more sensitive than computed tomography (CT) for detection of early infarction. In addition, MRI is equivalent to CT for the detection of acute intracerebral hemorrhage (ICH) and better than CT for the detection of chronic hemorrhage

MRI could, therefore, obviate the need for urgent CT in centers where brain MRI is readily available.

In order to identify ischemia, hemorrhage, and underlying structural changes that may identify stroke mimics, brain MRI protocols for the evaluation of stroke require the following sequences [54]:

●DWI

●Fluid-attenuated inversion recovery (FLAIR)

●High susceptibility sequence (eg, T2* or GRE, sensitive to blood)

Major drawbacks of MRI compared with CT are higher cost, limited availability/access, particularly in the emergency setting, a higher rate of patient intolerance and/or incompatibility, and longer scan time. However, newer ultrafast MRI imaging protocols can reduce acquisition times from the 15 to 20 minutes required by conventional MRI to five minutes or less [55,56], and one specialized stroke center found that routine use of MRI to screen patients prior to intravenous thrombolysis for suspected ischemic stroke was practical and safe [57]. Furthermore, MRI screening did not cause excessive treatment delays or lead to worse outcomes. On the other hand, MRI-specific selection criteria for acute thrombolysis of ischemic stroke have not been validated, and no randomized studies have compared CT and MRI screening in this setting.

Diffusion-weighted imaging (DWI) — DWI is based upon the capacity of MRI to visualize the freedom with which water moves (diffuses).

●Acute ischemic injury – In acute stroke, swelling of the ischemic brain parenchymal cells follows failure of the energy-dependent Na-K-ATPase pumps and is believed to increase the ratio of intracellular to extracellular volume fractions [58]. Intracellular water cannot diffuse as freely as extracellular water (also termed restricted diffusion), and the shift of water from the extracellular to the intracellular compartment can therefore be visualized with DWI. Because water shifts occur very quickly after stroke onset, DWI detects a signal related to the movement of water molecules between two closely spaced radiofrequency pulses. This technique can detect abnormalities due to ischemia within 3 to 30 minutes of onset [59-61], when conventional MRI and CT images would still appear normal.

DWI contains an additional component of T2 effect, and increased T2 signal due to vasogenic edema can "shine-through" on DWI images, making it difficult to distinguish vasogenic from cytotoxic edema on these images. This problem can be overcome by use of the apparent diffusion coefficient (ADC). The ADC provides a quantitative measure of the water diffusion. In acute ischemic stroke with cytotoxic edema, decreased water diffusion in infarcted tissue causes increased (hyperintense) DWI signal and a decreased ADC, visualized as hypointense signal on ADC maps of the brain. In contrast, vasogenic edema may cause increased DWI signal due to T2 shine-through, but since water diffusion is increased, there is also a hyperintense signal on the ADC map in this setting.

The decrease in ADC in the region of the infarct is a necessary transition on the way to infarction. The decrease in diffusion in the infarct is transient, lasting one to two weeks. It then actually reverses, passing through a phase of pseudonormalization and later becoming elevated and bright on ADC maps [62]. DWI abnormalities last somewhat longer due to the prominent T2 effect, but chronic infarction is not bright on DWI.

MRI and DWI utilizing higher magnetic field strengths of 3 Tesla (T) units are increasingly available in clinical settings. However, there is only limited and conflicting evidence regarding whether DWI obtained using 3 T MRI scanners is better for the detection of early (≤6 hours) and small infarcts compared with standard 1.5 T MRI [63,64]. Although seemingly advantageous because of improved signal-to-noise ratios, higher magnetic field strengths also introduce increased imaging artifacts and geometric distortions [65], and these artifacts may obscure early ischemic changes, particularly in regions of the brain near the skull base [64]. Thus, further refinement of higher field strength DWI imaging is needed to determine if such imaging is useful in acute ischemic stroke.

●Clinical utility of DWI – DWI is superior to noncontrast CT (NCCT) for the diagnosis of acute ischemic stroke in patients presenting within 12 hours of symptom onset [66]. This conclusion is based upon studies comparing cranial CT, DWI, and standard MRI, which have shown that abnormal DWI is a sensitive and specific indicator of ischemic stroke in patients presenting within six hours of symptom onset [67-72]. However, occasional patients with acute ischemic deficits have a normal DWI. In one retrospective report of 565 patients with acute ischemic stroke, a relevant lesion on DWI was apparent in 518 (92 percent), suggesting that DWI alone may miss an acute stroke in 8 percent of patients [72]. In these cases, follow-up MRI or CT may confirm an infarct [73,74]. In some of these patients, the stroke was a small brainstem lacune; in others, ischemia was seen on perfusion MRI in regions that had not yet become abnormal on DWI [73].

Even in patients with subacute ischemic stroke who delay seeking medical attention, DWI may add clinically useful information to standard MRI. In a prospective observational study of 300 patients with suspected stroke or transient ischemic attack (TIA) and a median delay of 17 days from symptom onset, DWI compared with T2 provided additional clinical information imaging for 108 patients (36 percent) such as clarification of diagnosis or vascular territory; this was considered likely to change management in 42 patients (14 percent) [75].

In the evaluation of acute ischemic stroke or TIA, the presence of multiple DWI lesions on the baseline MRI scan is associated with an increased risk of early lesion recurrence [76-78]. Furthermore, the presence of multiple DWI lesions of varying ages, as determined by the ADC value, is an independent predictor of future ischemic events [79].

●DWI-FLAIR mismatch – The DWI-FLAIR mismatch refers to evidence of an acute infarct on DWI imaging (hyperintense DWI lesion) but no corresponding abnormality on FLAIR imaging (isointense) [80]. The presence of a DWI-FLAIR mismatch is an indication that the stroke is relatively acute (ie, within 4.5 hours), as not enough time has passed for development of a hyperintense FLAIR signal, which results from vasogenic edema. This imaging finding has been used in clinical trials to select patients for treatment with intravenous thrombolysis when the time of stroke onset is unwitnessed or unknown [81].

Perfusion-weighted imaging (PWI) — PWI is useful to reveal ischemic regions of the brain. In contrast, DWI reveals evidence of ischemic injury, not ischemia itself.

●Methods – PWI uses MRI techniques to quantify the amount of magnetic resonance (MR) contrast agent reaching the brain tissue after an intravenous bolus. Analogous to CT perfusion (CTP) imaging described above , analysis of the characteristics of the contrast bolus passage through brain tissue can yield maps of the cerebral perfusion. These perfusion maps can display different characteristics of the cerebral perfusion, including cerebral blood flow (CBF), cerebral blood volume, mean transit time, time to peak of the contrast enhancement, and time to peak of the residue function.

Aside from gadolinium contrast bolus perfusion imaging, another method of MRI perfusion imaging is arterial spin labeling (ASL). Instead of using an intravascular contrast agent, ASL magnetically labels the blood entering the brain. ASL imaging within 24 hours of stroke symptom onset can depict perfusion defects and diffusion-perfusion mismatches [82]. In addition, CBF asymmetry on ASL appears to correlate with stroke severity and outcome.

●PWI/DWI mismatch – A mismatch between the PWI lesion and the DWI lesion (perfusion-diffusion mismatch or PWI/DWI mismatch, sometimes called a DWI/PWI mismatch) refers to evidence of a larger area of ischemia on PWI (ie, territory with critically low perfusion) relative to a smaller area of irreversible ischemic injury (ie, the infarct core) on DWI, suggesting the presence of salvageable brain tissue (ie, the ischemic penumbra) ( This type of mismatch is being used as an imaging marker to select patients who have salvageable brain tissue and are therefore likely to benefit from reperfusion. In the DEFUSE 3 trial, which studied patients with late-window acute ischemic stroke (6 to 16 hours after the time last known to be well), either CT or MR perfusion imaging was used to select patients for mechanical thrombectomy [83]. The study demonstrated a benefit of endovascular thrombectomy regardless of whether CT or MRI was used for patient selection, but the benefit was greater for patients selected using MR perfusion compared with patients selected using CT perfusion.

High susceptibility sequences — Increasing evidence supports the utility of high susceptibility MRI sequences (ie, GRE or T2* weighted images) for the early detection of acute thrombosis and occlusion involving the middle cerebral artery (MCA) or internal carotid artery (ICA). Acute thrombotic occlusion may appear on high susceptibility MRI as a hypointense (dark) signal within the MCA or ICA, often in a curvilinear shape; the diameter of the hypointense signal is larger than that of the contralateral unaffected vessel. This finding is called the susceptibility sign, and it is analogous to the hyperdense MCA sign described for CT imaging. (See 'Hyperdense vessel sign' above.)

In a retrospective report of 42 patients with stroke in the MCA territory who had MR imaging 95 to 360 minutes from stroke onset, a positive susceptibility sign corresponding to MCA or ICA occlusion was found in 30 (71 percent) [85]. The specificity of the sign was 100 percent. The overall sensitivity was 83 percent compared with MR angiography (MRA) but varied widely depending on location, from 38 percent for occlusions distal to the MCA bifurcation to 97 percent for occlusions proximal to the MCA trunk.

High susceptibility MRI sequences are also useful for the detection of acute intraparenchymal hemorrhage, especially if this is a concern after intra-arterial therapy, a situation where retained contrast is not easily distinguished from blood on CT [88]. 

MR angiography (MRA) — MRA to detect vascular stenosis or occlusion is done at many centers as part of a fast MRI protocol for acute ischemic stroke. Contrast-enhanced MRA shows promise for improved imaging of intracranial large vessels compared with the more established time-of-flight technique [89]. For the detection of intracranial large vessel stenosis and occlusion, contrast-enhanced MRA in various studies had sensitivities of 86 to 97 percent and specificities of 62 to 91 percent when compared with conventional angiography [38].

Population Referance No. 2

Patients suspected of having cerebral aneurysm

MRA can identify aneurysms 3 to 5 mm or larger . In one cohort study of 138 patients with suspected intracranial aneurysm, volume-rendering, 3D-time-of-flight MRA at 3 Tesla had a greater than 95 percent sensitivity and accuracy for detection of aneurysms.

CT and MR angiography — CTA and MRA are noninvasive tests that are useful for screening and presurgical planning. Both CTA and MRA can identify aneurysms ≥3 mm with a high degree of sensitivity [77], but they do not achieve the resolution of conventional angiography (ie, DSA). The sensitivity of CTA for the detection of ruptured aneurysms, using DSA as the gold standard, is 83 to 98 percent [78-84]. Small aneurysms (especially ≤2 mm) may not be reliably identified. Although small aneurysms rupture less frequently than large aneurysms [85], they are more common, and rupture of small aneurysms (approximately 5 mm or less) accounts for nearly one-half of SAH cases [86-88]. Therefore, DSA should be performed if CTA does not reveal an aneurysm in a patient with SAH [40].

As technology improves, the sensitivity and specificity of noninvasive imaging is also likely to improve [89]. A 2011 meta-analysis of CTA diagnosis of intracranial aneurysms found that, compared with single-detector CTA, use of multidetector CTA was associated with an overall improved sensitivity and specificity for aneurysm detection (both >97 percent) as well as improved detection of smaller aneurysms ≤4 mm in diameter [90]. Another systematic review and meta-analysis restricted to patients with SAH had similar findings [91].

While a "spot sign" (ie, contrast extravasation) on CTA is associated with risk of hemorrhage expansion or rebleeding in patients with intracerebral hemorrhage, this is not the case for SAH [92,93]. It is likely that this sign, while appearing similar, actually reflects different processes when observed in SAH versus intracerebral hemorrhage.  

Population Referance No. 3

Patients suspected of having intracranial vascular malformation

Magnetic resonance imaging — MRI is sensitive for delineating the location of the brain AVM nidus and often an associated draining vein. It also has unique sensitivity in demonstrating remote bleeding related to these lesions. Dark flow voids are appreciated on T1- and T2-weighted studies . Similar to CTA, magnetic resonance angiography (MRA) a high sensitivity and specificity (98 and 99 percent, respectively) for the diagnosis of an underlying intracranial vascular malformation.

Population Referance No. 4

Patients suspected of having cerebral venous sinus compression or thrombosis

Cerebral vein and dural sinus thrombosis (CVT) is less common than most other types of stroke but can be more challenging to diagnose. Due to the widespread use of MRI and rising clinical awareness, CVT is recognized with increasing frequency. In addition, it is now known to have a more varied clinical spectrum than previously realized. Because of its myriad causes and presentations, CVT is a disease that may be encountered not only by neurologists and neurosurgeons, but also by emergency clinicians, internists, oncologists, hematologists, obstetricians, pediatricians, and family practitioners.

For patients with any presentation raising concern for CVT, we recommend urgent neuroimaging with brain MRI and magnetic resonance (MR) venography, or with cranial CT with CT venography if MRI is not an option. The clear demonstration of absence of flow and intraluminal venous thrombus by CT or MRI is the most important finding for confirming the diagnosis. However, these findings are not always evident, and the diagnosis may rest on imaging features demonstrated by MR venography or CT venography showing only absence of flow in a venous sinus or cortical vein.

A number of normal anatomic variants may mimic sinus thrombosis, including sinus atresia, sinus hypoplasia, asymmetric sinus drainage, and normal sinus filling defects associated with arachnoid granulations or intrasinus septa. For example, a study of 100 subjects (without CVT) with normal brain MRI found artifactual transverse sinus flow gaps on MR venography (in nondominant or codominant but not in dominant transverse sinuses) in 31 percent . Another report of 100 subjects without venous pathology found asymmetric lateral sinuses in 49 percent and partial or total absence of one lateral sinus in 20 percent.

MRI using gradient echo T2* susceptibility-weighted sequences in combination with MR venography is the most sensitive imaging method for demonstrating the thrombus and the occluded dural sinus or vein. The characteristics of the MRI signal depend on the age of the thrombus:

●In the first five days, the thrombosed sinuses appear isointense on T1-weighted images and hypointense on T2-weighted images

●Beyond five days, venous thrombus becomes more apparent because signal is increased on both T1- and T2-weighted images

●After the first month, thrombosed sinuses exhibit a variable pattern of signal, which may appear isointense

On gradient echo T2*-weighted MRI sequences, the clot can be directly visualized as an area of hypointensity in the affected cortical vein and/or sinus. However, a chronically thrombosed sinus may still demonstrate low signal on these sequences. Limited data from a series of 28 patients with CVT suggest that the presence of hyperintensities in the veins or sinuses on diffusion-weighted MRI sequences predicts a low recanalization rate.

Parenchymal brain lesions secondary to venous occlusion, including brain swelling, edema, or venous infarction, appear as hypointense or isointense on T1-weighted MRI, and hyperintense on T2-weighted MRI. Hemorrhagic venous infarcts appear as hyperintense lesions on both T1 and T2 MRI sequences.

Agreement between observers for the diagnosis of CVT with MRI varies with the location of sinus or vein thrombosis. It is good or very good for most of the occluded sinus and veins; moderate to very good for the left lateral sinus and straight sinus; and poor to good for the cortical veins. The diagnosis of isolated cortical vein thrombosis remains difficult to establish with MR venography. Use of T2*-weighted MRI may enable a diagnosis of isolated cortical vein thrombosis by demonstrating clot as an area of hypointensity [.

MR venography — MR venography, usually performed using the time-of-flight (TOF) technique, is useful for demonstrating absence of flow in cerebral venous sinuses, though interpretation can be confounded by normal anatomic variants such as sinus hypoplasia and asymmetric flow. Other MR techniques may be useful to distinguish these variants from venous thrombosis. Contrast-enhanced MR venography can provide better visualization of cerebral venous channels, and gradient echo or susceptibility-weighted sequences will show normal signal in a hypoplastic sinus and abnormally low signal in the presence of thrombus. A chronically thrombosed hypoplastic sinus will show absence of flow on two-dimensional TOF MR venography and enhancement on contrast-enhanced MRI and MR venography.

Population Referance No. 5

Patients with pulsatile tinnitus

Suspected vascular tinnitus — Patients with infrequent episodes of pulsatile tinnitus or those with short-duration, mild tinnitus can be initially observed.

However, because frequent or constant pulsatile tinnitus can herald a potentially life-threatening illness, all of these patients require evaluation by an otolaryngologist or neurotologist. When physical examination does not reveal a specific vascular or musculoskeletal source in these patients, further investigation to rule out a central nervous system lesion such as a dural arteriovenous fistula (AVF), arteriovenous malformation (AVM) or aneurysm, or a skull base tumor should be carried out [34].

The gold standard for AVF diagnosing intracranial vascular lesions is angiography. These lesions often can also be diagnosed noninvasively with magnetic resonance (MR) angiography or computed tomographic (CT) angiography . High-resolution CT scanning is required to delineate the extent of involvement of the skull base if a paraganglioma is suspected and may be sufficient to evaluate other central nervous system lesions in selected patients. MRI can diagnose a Chiari malformation, vasculitis, central nervous system tumors, and multiple sclerosis and may indicate the presence of increased intracranial pressure (such as that seen in pseudotumor cerebri) or tumors. Many patients require both contrast MRI and contrast CT because of the varied nature of disorders that cause pulsatile tinnitus. If both of these studies are normal, and suspicion for a vascular lesion remains high, angiography or MR angiography is warranted.

Our protocol involves audiometric testing followed by an extensive history and physical exam, which guides additional diagnostic testing. When an intracranial vascular lesion is suspected, we obtain an MRI with contrast initially, followed by CT/CT angiography and subsequent interventional angiography in appropriate circumstances.

Population Referance No. 6

Patients suspected of having carotid stenosis or occlusion

The magnetic resonance angiography (MRA) techniques most often employed for evaluating the extracranial carotid arteries utilize either two- or three-dimensional time-of-flight (TOF) MRA or gadolinium-enhanced MRA (also known as contrast-enhanced MRA or CEMRA). 

MRA produces a reproducible three-dimensional image of the carotid bifurcation with good sensitivity for detecting high-grade carotid stenosis. In earlier studies, MRA was found to generally overestimate the degree and length of stenosis. However, a later study of three-dimensional TOF MRA found that it did not overestimate the degree of stenosis when corresponding MRA and digital subtraction angiography (DSA) projections were compared.

CEMRA offers several advantages over traditional TOF techniques. The use of a paramagnetic agent acting as a vascular contrast allows for higher quality images that are less prone to artifacts.

Both TOF MRA and CEMRA are accurate for the identification of high-grade carotid artery stenosis and occlusion, but appear to be less accurate for detecting moderate stenosis. The sensitivities of either MRA technique for the identification of carotid artery occlusion or severe stenosis were similar and ranged from 91 to 99 percent, while specificities ranged from 88 to 99 percent.

Compared with carotid duplex ultrasound, MRA is less operator-dependent and does produce an image of the artery. However, MRA is more expensive and time-consuming than carotid duplex ultrasound and is less readily available. Furthermore, MRA may not be performed if the patient is critically ill, unable to lie supine, or has claustrophobia, a pacemaker or ferromagnetic implants. In different series, up to 17 percent of MRA studies are incomplete because the patient could not tolerate the study or could not lie still enough to produce an image of adequate quality for interpretation. Renal insufficiency is a relative contraindication to the use of gadolinium.

Advanced magnetic resonance imaging techniques are being studied to assess whether changes in carotid plaque characteristics, such as rupture of fibrous cap and intraplaque hemorrhage, are reliably associated with an increased risk of subsequent stroke in patients with asymptomatic carotid atherosclerosis. 

Population Referance No. 7

Patients suspected of having cervicocranial arterial dissection

Arterial dissections are a common cause of stroke in the young, but may occur at any age. Dissection occurs when structural integrity of the arterial wall is compromised, allowing blood to collect between layers as an intramural hematoma.

Vascular imaging is used to confirm an initial diagnosis of cervicocephalic dissection and to guide serial treatment decisions. In most centers, conventional angiography has been supplanted by noninvasive approaches, particularly brain MRI with MRA and cranial CT with CTA. A systematic review published in 2009 found that the sensitivity and specificity of MR techniques and CTA for the diagnosis of cervicocephalic arterial dissection are relatively similar. We reserve the use of conventional angiography for younger patients when clinical suspicion for dissection remains high despite negative noninvasive imaging. There is no need for conventional angiography if the diagnosis of cerebral or cervical artery dissection is clear using CTA or MRA.

Angiographic findings of dissection include a string sign , tapered stenosis or occlusion or flame-shaped occlusion, intimal flap, dissecting aneurysm, distal pouch, and underlying arteriopathy. Multimodal CT or MRI, including CTA or MRA, may illustrate luminal abnormalities, arterial wall expansion, intramural hematoma, and surrounding structures. In a population-based study of 48 consecutive patients with cervical artery dissection, the diagnostic neuroimaging patterns were an elongated tapered stenosis, a tapered occlusion, and a dissecting aneurysm in 48, 35, and 17 percent, respectively. In a prospective European study of patients with spontaneous vertebral artery dissection, the most frequent diagnostic neuroimaging finding on MRI was intramural hematoma, which was observed in 91 percent of 157 vertebral artery dissections.

Extracranial carotid dissections typically occur 2 cm or more beyond the carotid bifurcation, near or adjacent to the level of the skull base. Intracranial carotid dissections are most frequent in the supraclinoid segment. Vertebral artery dissection most often occurs in the cervical transverse processes of C6 to C2 (V2 segment) or the extracranial segment between the transverse process of C2 and the foramen magnum at the base of the skull (V3 segment).

The pathognomonic crescent sign of intramural hematoma is formed by an eccentric rim of hyperintensity surrounding a hypointense arterial lumen on MRI. This crescent sign has traditionally been described on T1-weighted fat-saturation MRI sequences, but may be apparent on other sequences such as diffusion-weighted imaging  or even apparent on CT angiography. The degree of MRI hyperintensity and the methemoglobin content of the intramural hematoma varies with age of the lesion. Dissections of the horizontal vertebral artery segment may be difficult to diagnose as the classic crescent may be missing due to orientation of the vessel and the vertebral venous plexus may also appear hyperintense. The orientation of the vertebral artery may also limit delineation of a crescent, as the lumen may be patent yet surrounded by a more irregular "suboccipital rind" sign. Assessment of multimodal CT or MRI source images is crucial to define vessel wall abnormalities.

Carotid duplex and transcranial Doppler ultrasonography (TCD) may be used to screen for suspected dissection, or to monitor therapy. However, carotid duplex detects abnormalities in only 68 to 95 percent of cases. In addition, duplex and transcranial Doppler have a suboptimal yield for identifying arterial dissection near the skull base and vertebral artery dissection within the transverse foramina. In addition, ultrasound is unreliable for detecting carotid artery dissection in patients with an isolated Horner syndrome [. Therefore, confirmation with MRA or CTA should be pursued in ultrasound-negative cases when the clinical history is suggestive of dissection.

The pattern of brain ischemia on diffusion-weighted MRI may be influenced by the patency of the dissected artery, with territorial rather than borderzone infarcts apparent when there is complete occlusion of the vessel. The advent of high-resolution 3 Tesla MRI has made it possible to detail interval recanalization, degree of stenosis, formation of dissecting aneurysms and the appearance of new dissections as part of serial imaging evaluations. Periarterial inflammation associated with dissection may also be visualized with such high-resolution MRI techniques

Population Referance No 8

Patients suspected of having atherosclerotic renal artery stenosis

Diagnostic performance of MRA of the abdomen for evaluation of renal anatomy in potential living renal donors has improved with the evolution of contrast-enhanced MRA techniques. Recent studies have shown contrast-enhanced MRA to have good sensitivity and specificity for detection of renal arterial and venous anomalies. Three studies reported sensitivity and specificity of 90% or higher for renal arterial anatomy. (12–14) One study examined the ability of contrast-enhanced MRA to detect arterial, venous, ureteral, or parenchymal anomalies during the presurgical evaluation process for laparoscopic nephrectomy. (15) This study found that preoperative MRA agreed completely with surgical findings in 21 of 28 cases (75%). In this study, the laparoscopic surgical procedure was successful in 27 of 28 cases (96%) and only 1 case required conversion to open nephrectomy, suggesting that some oversights on MRA may not be clinically significant. Furthermore, studies comparing contrast-enhanced MRA to alternatives such as computed tomographic angiography (CTA) and digital subtraction angiography have reported comparable results. (14, 16–18) However, concerns have been raised regarding the ability of MRA or CTA to detect mild or distal-moderate fibromuscular dysplasia (FMD) that can be seen on conventional renal angiography. (19) The prevalence of FMD is about 2% to 6.6% in angiographic case series, and it is unclear what effect donor nephrectomy may have on the subsequent development of hypertension in asymptomatic potential renal donors who have silent FMD. (19)

Population Referance No. 9

Patients with suspected chronic mesenteric ischemia

A high index of clinical suspicion is important for making a timely diagnosis of chronic mesenteric ischemia, which is often delayed as patients are often first evaluated for other etiologies (especially malignancy) as an explanation for weight loss. The average delay from the beginning of symptoms to diagnosis or treatment was 10.7 months in one review and 15 months in another.

When available, CT angiography is the preferred initial diagnostic imaging modality as it allows for rapid and accurate three-dimensional renderings of the intestinal vasculature and bowel timed to coincide with peak arterial or venous enhancement. The study should be performed with intravenous contrast, as well as a neutral oral contrast (barium or water) to better evaluate the bowel wall.

CT angiography has sensitivities and specificities exceeding 90 percent for the diagnosis of chronic mesenteric ischemia due to atherosclerosis [25-28]. High-grade mesenteric vascular stenoses in at least two major vessels (celiac, superior mesenteric, or inferior mesenteric) must be established. Evidence for collateral formation to compensate for the reduced main arterial flow is typically present. Contrast-enhanced magnetic resonance angiography (MRA) is also highly sensitive for detecting arterial stenoses at the origins of the celiac or mesenteric arteries; however, the technique is much less reliable for detecting more distal lesions. Quantification of postprandial flow on MR angiography may prove useful as a diagnostic modality. Noncontrast MR angiography may be a useful alternative to CT angiography in patients who cannot tolerate an intravenous contrast load. 

Population Referance No. 10

Patients with abdominal aortic aneurysm who are to undergo elective repair of the aneurysm

CT angiography of the abdomen and pelvis with ≤2.5 mm cuts with three-dimensional (3D) reconstruction is obtained. Although two-dimensional (2D) CT images can be used, measurement errors (aortic diameter, aortic length) can occur due to volume averaging. In addition, aortic diameter measurements will be overestimated if the aorta is angulated and the longitudinal axis is not perpendicular to the imaging plane. CT angiography with 3D reconstruction allows measurements to be made that are perpendicular to the true axis of the aorta. Centerline length measurements can also be obtained with 3D reconstruction. 3D length measurements are more accurate than 2D measurements and can improve graft sizing, particularly in patients with tortuous vessels.

Magnetic resonance (MR) angiography can be used for preoperative endograft planning preoperatively; however, gadolinium administration in the setting of renal dysfunction is a relative contraindication.

Population Referance No 11

Patients requiring evaluation of the portal and/or hepatic venous system; patients requiring evaluation of the systemic venous system.

Chronic portal vein thrombosis (PVT) is diagnosed with abdominal imaging. Our approach is to start with abdominal ultrasound with Doppler imaging, followed by a computed tomographic (CT) scan or magnetic resonance imaging (MRI) to confirm the diagnosis and to look for predisposing conditions, such as hepatocellular carcinoma. We start with Doppler ultrasound because it is inexpensive and can identify biliary pathology that may lead to abdominal pain. It is reasonable to start with a CT or MRI if suspicion for chronic PVT is high or if there is generalized abdominal pain, in which case the differential diagnosis is large.

Abdominal MRI — Findings on abdominal MRI in a patient with PVT include portal vein occlusion as well as collateral veins around the porta hepatis. On MRI angiography, PVT appears as a filing defect that partially or completely occludes the vessel lumen in the portal venous phase [25]. In one study, MRI had a sensitivity of 100 percent and a specificity of 99 percent for detecting PVT. MRI is sensitive for detecting submucosal, serosal, and periesophageal collaterals and may demonstrate portal flow reduction or inversion.

Population Referance No. 12

Patients with suspected atherosclerotic disease of the lower extremity in whom angiography would otherwise be indicated and in whom MRA would obviate the need for angiography

Duplex ultrasonography is commonly used in conjunction with the ankle-brachial index (ABI) to identify the location and severity of arterial obstruction. Advanced vascular imaging (computed tomographic [CT] angiography, magnetic resonance [MR] angiography, catheter-based arteriography) is usually reserved for patients in whom there remains uncertainty following noninvasive testing, or in whom intervention is anticipated.

The main goal of advanced vascular imaging is to provide the clinician with information necessary for planning an intervention. In general, we suggest computed tomography (CT) angiography as the initial study for advanced vascular imaging, unless the patient has severe renal dysfunction or an intravenous contrast allergy (and cannot be adequately pretreated). If the patient has diabetes without acute renal insufficiency, a more accurate measurement of stenosis may be achieved by magnetic resonance (MR) angiography (which does not have the confounding issue of shadowing from calcification). MR angiography may also show vascular wall thickening better, as in patients with vasculitis.

MR angiography – MR angiography is a less invasive alternative to contrast arteriography and does not necessarily require intravenous contrast. Both phase-contrast (PC) and time-of-flight (TOF) MR angiography are noncontrast techniques that detect blood by virtue of its movement compared with static surrounding tissues. On the other hand, contrast-enhanced (CE) MR angiography uses an intravenous contrast and relies on the T1 shortening effect of the contrast media within the arterial system. Although MR angiography is time efficient and cost effective for the assessment of lower extremity PAD, patients who suffer from severe claustrophobia or have pacemakers and/or some other metallic implants are not candidates. The risks associated with gadolinium in patients with renal dysfunction/failure is discussed separately.

Population Referance No. 13

Patients with known atherosclerotic disease of the lower extremity who are being evaluated for bypass surgery and in whom angiography fails to identify runoff vessels suitable for bypass

MRA of the pelvis and lower extremities has emerged as an important tool for surgical planning, particularly to identify patent distal run-off vessels when surgical revascularization is considered. (4–7) In addition, MRA has been widely used to evaluate the recurrent symptoms in patients who have undergone either angioplasty or surgical revascularization. A meta-analysis of 34 studies conducted by Koelemay et al. (8) found that MRA was accurate for identifying stenosis (>50%) or occlusions in the aorto-iliac, femoropopliteal, and infrapopliteal regions. Baum et al. (9) found that MRA is more sensitive for identifying runoff vessels compared with conventional angiography. Use of vessels visible only on MRA for bypass surgery provides an opportunity for limb salvage and when compared with bypass to angiographically visible vessels, graft-patency and limb-salvage outcomes are similar. (10) These roles of MRA are recognized by the American College of Radiology Appropriateness Criteria. (11)

Supplemental Information

Practice Guidelines and Position Statements

American Association of Neurological Surgeons (AANS), American Society of Neuroradiology (ASNR), Cardiovascular and Interventional Radiology Society of Europe (CIRSE), Canadian Interventional Radiology Association (CIRA), Congress of Neurological Surgeons (CNS), European Society of Minimally Invasive Neurological Therapy (ESMINT), European Society of Neuroradiology (ESNR), European Stroke Organization (ESO), Society for Cardiovascular Angiography and Interventions (SCAI), Society of Interventional Radiology (SIR), Society of NeuroInterventional Surgery (SNIS), and World Stroke Organization (WSO): Multisociety consensus quality improvement revised consensus statement for endovascular therapy of acute ischemic stroke (2018)

American Heart Association (AHA)/American Stroke Association (ASA): Guidelines for the early management of patients with acute ischemic stroke, update (2019)

●Society of Interventional Radiology (SIR), Cardiovascular and Interventional Radiology Society of Europe (CIRSE), and Interventional Radiology Society of Australasia (IRSA): A joint position statement on the role of interventional radiologists in acute ischemic stroke interventions (2019)

●US Department of Veterans Affairs (VA) and US Department of Defense (DoD): Clinical practice guideline for the management of stroke rehabilitation (2019)

●American College of Radiology (ACR): ACR Appropriateness Criteria cerebrovascular disease (2017)

●American Academy of Neurology (AAN): Evidence-based guideline − The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke (2010, reaffirmed 2016)

U.S. Preventive Services Task Force Recommendations

Not applicable.

Medicare National Coverage

 Compliance with the provisions in this policy is subject to monitoring by post payment data analysis and subsequent medical review. Title XVIII of the Social Security Act, Section 1862(a)(1)(A) states " ...no Medicare payment shall be made for items or services which are not reasonable and necessary for the diagnosis and treatment of illness or injury...". Furthermore, it has been longstanding CMS policy that "tests that are performed in the absence of signs, symptoms, complaints, or personal history of disease or injury are not covered unless explicitly authorized by statute".

Ongoing and Unpublished Clinical Trials

N/A

References

9.      Baum RA, Rutter CM, Sunshine JH et al. Multicenter trial to evaluate vascular magnetic resonance angiography of the lower extremity. JAMA 1995; 274(11):875-80.

10. Carpenter JP, Golden MA, Barker CF et al. The fate of bypass grafts to angiographically occult runoff vessels detected by magnetic resonance angiography. J Vasc Surg 1996; 23(3):483-9.

11. American College of Radiology Appropriateness Criteria. www.acr.org/dyna/?doc=departments/appropriateness_criteria/toc.html

12. Fink C, Hallscheidt PJ, Hosch WP et al. Preoperative evaluation of living renal donors: value of contrast-enhanced 3D magnetic resonance angiography and comparison of three rendering algorithms. Eur Radiol 2003; 13(4):794-801.

13. Jha RC, Korangy SJ, Ascher SM et al. MR angiography and preoperative evaluation for laparoscopic donor nephrectomy. AJR Am J Roentgenol 2002; 178(6):1489-95.

14. Rankin SC, Jan W, Koffman CG. Noninvasive imaging of living related kidney donors: evaluation with CT angiography and gadolinium-enhanced MR angiography. AJR Am J Roentgenol 2001; 177(2):349-55.

15. Israel GM, Lee VS, Edye M et al. Comprehensive MR imaging in the preoperative evaluation of living donor candidates for laparoscopic nephrectomy: initial experience. Radiology 2002; 225(2):427-32.

16. Giessing M, Kroencke TJ, Taupitz M et al. Gadolinium-enhanced three- dimensional magnetic resonance angiography versus conventional digital subtraction angiography: which modality is superior in evaluating living kidney donors? Transplantation 2003; 76(6):1000-2.

17. Halpern EJ, Mitchell DG, Wechsler RJ et al. Preoperative evaluation of living renal donors: comparison of CT angiography and MR angiography. Radiology 2000; 216(2):434-9.

18. Hussain SM, Kock MC, IJzermans JN et al. MR imaging: a “one-stop shop” modality for preoperative evaluation of potential living kidney donors. Radiographics 2003; 23(2):505-20.

19. Andreoni KA, Weeks SM, Gerber DA et al. Incidence of donor renal fibromuscular dysplasia: does it justify routine angiography? Transplantation 2002; 73(7):1112-6.

20. UpToDate  Literature review current through: Mar 2020. | This topic last updated: Feb 25, 2020.

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