Coverage Policy Manual
Policy #: 2014009
Category: Surgery
Initiated: April 2014
Last Review: March 2018
  Endovascular Procedures for Intracranial Arterial Disease and Extracranial Vertebral Artery Disease

Description:
Intracranial arterial disease includes thromboembolic events, vascular stenoses, and aneurysms. Endovascular techniques have been investigated for treatment of intracranial arterial disease, as an alternative to intravenous tissue plasminogen activator (tPA) and supportive care for acute stenosis and as an alternative to risk factor modification for chronic stenosis. For cerebral aneurysms, stent-assisted coiling has been evaluated as an alternative to endovascular coiling in patients whose anatomy is not amenable to simple coiling.
 
Background
Cerebrovascular diseases include a range of processes affecting the cerebral vascular system, including arterial thromboembolism, arterial stenosis, and arterial aneurysms, all of which can lead to restrictions in cerebral blood flow due to ischemia or hemorrhage. Endovascular techniques, including endovascular pharmacologic thrombolysis, endovascular mechanical embolectomy; using one of several types of devices, endovascular deployment of several types of stents, and angioplasty with or without stenting, have been investigated for treatment of cerebrovascular diseases.
 
Acute Stroke
Acute stroke is the third leading cause of death in the U.S., Canada, Europe and Japan and is the leading cause of adult disability in the U.S. (Meyers, 2011). The acute brain injury of stroke has 2 major types: ischemic and hemorrhagic. Of patients with stroke presenting to the emergency department, approximately 80% will be diagnosed with ischemic brain injury. Distinguishing between these types of stroke is important because the established treatments for each are significantly different. The focus of treatment in ischemic stroke is reperfusion of hypoxic brain tissue, while the focus in hemorrhagic stroke is correction of the condition which led to bleeding. If the underlying cause of ischemia is systemic hypotension, this must be corrected. Far more commonly, however, a clot occluding an intracranial vessel is the cause of ischemic stroke. Recanalization of the vessel, particularly in the first few hours after occlusion, has been shown to reduce rates of disability and death (Rha, 2007).
 
While spontaneous thrombolysis does occur, treatment of ischemic stroke has focused on the use of intravenous tissue plasminogen activator (tPA) to promote dissolution of the clot and subsequent restoration of blood flow to the ischemic area of the brain. The use of intravenous tPA within 3 hours of stroke onset for selected patients is the standard of care for ischemic stroke treatment. Despite its benefits, widespread implementation of intravenous tPA is challenging. Reperfusion benefits decrease over time; infarcted brain tissue will not recover. In most states, fewer than 10% of ischemic stroke patients arrive in the hospital in time for intravenous tPA within the 3-hour window for its use. Because tPA is associated with an increased risk of intracranial bleeding, it is contraindicated in hemorrhagic stroke and in some ischemic stroke patients in which the risk of bleeding outweighs potential benefit, such as those with mild or resolving symptoms, hypocoagulable state, or advanced age.
 
There are several ways in which endovascular interventions may be used as a treatment for acute stroke. For patients who present with acute stroke within the time window for thrombolysis and meet other clinical criteria for intravenous tPA, endovascular interventions may be used in combination with thrombolysis. For patients who are not candidates for thrombolysis (e.g., who present past the time window for thrombolysis), endovascular interventions can be considered as an alternative to standard conservative medical therapy.
 
Intravenous tPA has improved outcomes for many, but not all, ischemic stroke patients. Researchers have studied intra-arterial tPA, transcranial ultrasound energy, and mechanical clot destruction or clot removal as an alternative, or second line, to the established intravenous tPA therapy. Clots can be defined as located in large or small vessels. Large intracranial arteries include the internal carotid, Circle of Willis and the first 2 branches of the anterior (A1 and A2), middle (M1 and M2), and posterior (P1 and P2) cerebral arteries. These can be accessed with a catheter; further branches of the cerebral circulation are defined as small vessels and are too tortuous to be mechanically accessed with available technology.
 
Several types of endovascular treatments for ischemic strokes have been considered:
 
  1. Intra-arterial fibrinolytic therapy (i.e., intra-arterial tPA). Although tPA only has approval from the U.S. Food and Drug Association (FDA) for its intravenous route of delivery, intra-arterial tPA has been considered for patients who fail to present within the window of treatment for intravenous tPA or who have failed to show benefit from intravenous tPA. It is also frequently used in conjunction with other endovascular devices.
  2.          
  3. Acute angioplasty and/or stent deployment. Balloon angioplasty and balloon-expandable stents have been investigated for acute stroke. Given concern for higher risks of complications in the cerebral vasculature with the use of balloon-expandable stents, self-expanding stents have gained more attention. At present, no balloon- or self-expandable stent has FDA approval for treatment of acute stroke.
  4.         
  5. Endovascular mechanical embolectomy. Endovascular embolectomy devices remove or disrupt clots by a number of mechanisms. Four devices are considered here (see “Regulatory Status”), the Merci® Retriever, Penumbra System®, Solitaire™ Flow Restoration Device and the Trevo® Retriever. With the Merci® device, a microcatheter is passed through the thrombus from a larger, percutaneous catheter positioned proximal to the occlusion. A helical snare is deployed, and the catheter and clot are withdrawn together. With the Penumbra® device, an opening at the tip of the percutaneous catheter utilizes suction to extract the clot. Both the Solitaire Flow Restoration Device and the Trevo Retriever are retrievable stents, which are positioned to integrate the clot with the stent for removal with the stent’s struts.
 
This policy focuses on the four devices with an indication for endovascular embolectomy for acute stroke.
 
An additional clinical situation in which endovascular therapies may be used in the treatment of acute ischemic stroke is in the setting of cerebral vasospasm following intracranial (subarachnoid) hemorrhage. Delayed cerebral ischemia (DCI) occurs about 3-14 days following the acute bleed in about 30% of patients experiencing subarachnoid hemorrhage, and is a significant contributor to morbidity and mortality in patients who survive the initial bleed. In cases refractory to medical measures, rescue invasive therapies including intra-arterial vasodilator infusion therapy (eg, calcium channel blockers) and transluminal balloon angioplasty may be used (Abruzzo, 2012; Diringer, 2011). The mechanism of disease, patient population, and time course of therapy differ for DCI occurring post-subarachnoid hemorrhage compared with ischemic stroke due to atheroembolic disease. Therefore, this indication for endovascular intervention will not be addressed in this policy.
 
Intracranial Atherosclerotic Disease
It is estimated that intracranial atherosclerosis causes about 8% of all ischemic strokes. Intracranial stenosis may contribute to stroke in 2 ways: either due to embolism or low flow ischemia in the absence of collateral circulation. Recurrent annual stroke rates are estimated at 4% to 12% per year with atherosclerosis of the intracranial anterior circulation and 2.5% to 15% per year with lesions of the posterior (vertebrobasilar) circulation. Medical treatment typically includes either anticoagulant therapy (i.e., warfarin) or antiplatelet therapy (e.g., aspirin). The “Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) trial was a randomized trial that compared the incidence of stroke brain hemorrhage or death among patients randomized to receive either aspirin or warfarin. The trial found that over a mean 1.8 years of follow-up, warfarin provided no benefit over aspirin and was associated with a significantly higher rate of complications. In addition, if symptoms could be attributed to low flow ischemia, agents to increase mean arterial blood pressure and avoidance of orthostatic hypotension may be recommended. However, medical therapy has been considered less than optimal. For example, in patients with persistent symptoms despite antithrombotic therapy, the subsequent rate of stroke or death has been extremely high, estimated in 1 study at 45%, with recurrent events occurring within 1 month of the initial recurrence. Surgical approaches have met with limited success. The widely quoted extracranial-intracranial (EC/IC) bypass study randomized 1377 patients with symptomatic atherosclerosis of the internal carotid or middle cerebral arteries to medical care or EC/IC bypass. The outcomes in the 2 groups were similar, suggesting that the EC/IC bypass is ineffective in preventing cerebral ischemia. Due to inaccessibility, surgical options for the posterior circulation are even more limited.
 
Percutaneous transluminal angioplasty (PTA) has been approached cautiously for use in the intracranial circulation, due to technical difficulties in catheter and stent design and the risk of embolism, which may result in devastating complications if occurring in the posterior fossa or brain stem. However, improvement in the ability to track catheterization, allowing catheterization of tortuous vessels, and the increased use of stents have created ongoing interest in exploring PTA as a minimally invasive treatment of this difficult-to-treat population. The majority of published studies of intracranial PTA has focused on the vertebrobasilar circulation. Two endovascular devices have FDA approval for treatment of symptomatic intracranial stenosis and are considered here (see “Regulatory Status”).
 
Cerebral Aneurysms
Compared with acute ischemic stroke, cerebral aneurysms have a much lower incidence among the U.S. population, with prevalence between 0.5% and 6% of the population (Meyers, 2009). However, they are associated with significant morbidity and mortality due to subarachnoid hemorrhage resulting from aneurysm rupture. Surgical clipping of intracranial aneurysms has been used since the 1960s, but the feasibility of clipping for aneurysms depends on the aneurysm location. Intracranial stents are also being used in the treatment of cerebral aneurysms. Stent-assisted coiling began as an approach to treat fusiform or wide-neck aneurysms in which other surgical or endovascular treatment strategies may not be feasible. As experience grew, stenting was also used in smaller berry aneurysms as an approach to decrease the rate of retreatment needed in patients who receive coiling. A randomized trial has demonstrated that treatment of ruptured intracranial aneurysms with coiling leads to improved short-term outcome compared with surgical clipping; however, patients who receive coiling need more repeat/follow-up procedures. In 2011, the Pipeline® Embolization Device, which falls into a new device category called “intracranial aneurysm flow diverters,” or flow-diverting stent, received FDA premarket approval for endovascular treatment of large or giant wide-necked intracranial aneurysms in the internal carotid artery. The Pipeline device is a braided, wire mesh device that is placed within the parent artery of an aneurysm to redirect blood flow away from the aneurysm with the goal of preventing aneurysm rupture and possibly decreasing aneurysm size.
 
Regulatory Status
Several devices for endovascular treatment of intracranial arterial disease have received clearance by FDA through either the 510(k) process or through the humanitarian device exemption (HDE) process. By indication, approved devices are as follows:
 
Acute Stroke
    1. The Merci® Retriever (Concentric Medical, Mountain View, CA). In August 2004, the Merci® Retriever (Concentric Medical, Mountain View, CA) was cleared by FDA through the 510(k) process. This device was judged equivalent to a predicate device, the Concentric Retriever, which was indicated for endovascular foreign body removal. The FDA clearance indicated that the Mechanical Embolus Removal in Cerebral Ischemia (MERCI) Clinical Study established that no new issues of safety and effectiveness exist when the Merci Retriever is used for thrombus removal versus foreign body removal from the neurovasculature. A modified Merci Retriever, also manufactured by Concentric Medical Inc., received 510(k) clearance from FDA in May 2006. The clearance notes that the Modified Merci Retriever is intended to restore blood flow in the neurovasculature by removing thrombus in patients experiencing ischemic stroke. Patients who are ineligible for intravenous tPA or who fail intravenous tPA therapy are candidates for treatment. The device also has clearance for retrieval of foreign bodies misplaced during interventional radiologic procedures in the neuro, peripheral, and coronary vasculature.  
    2. The Penumbra System® (Penumbra Inc., Alameda, CA). In December 2007, the Penumbra System® (Penumbra Inc., Alameda, CA) was cleared through the 510(k) process. FDA determined that this device was substantially equivalent to existing devices for use in the revascularization of patients with acute ischemic stroke secondary to intracranial large vessel occlusive disease (in the internal carotid, middle cerebral - Ml and M2 segments, basilar, and vertebral arteries) within 8 hours of symptom onset.     
    3. The Solitaire™ FR device (Covidien/ ev3 Neurovascular, Irvine, CA). In March 2012, the Solitaire™ FR device was cleared for marketing by FDA through the 510(k) process. FDA determined that this device was substantially equivalent to the Merci Retriever device, based on a randomized controlled trial (RCT) of 113 patients submitted to FDA comparing the Merci and Solitaire devices. Indications for the device are patients with ischemic stroke due to large intracranial vessel occlusion who are ineligible for intravenous tPA, or who fail intravenous tPA.
    4. The Trevo Pro Retriever™ device (Stryker Neurovascular, Kalamazoo, MI). In August 2012, the Trevo Pro Retriever™ device (Stryker Neurovascular, Kalamazoo, MI) was cleared for marketing by FDA through the 510(k) process. FDA determined that this device was substantially equivalent to the Merci Retriever device, based on an RCT of 178 patients from 27 centers in the U.S. and Europe that compared the Trevo device with the Merci device. Indications for the device are patients with acute ischemic stroke due to large intracranial vessel occlusion who are ineligible for or fail intravenous tPA. Later versions of the Trevo® Retriever are called the Modified Trevo® Retriever, the Trevo® ProVue Retriever, and the Modified Trevo® ProVue Retriever; the name Trevo Retriever is used throughout this Assessment. FDA product code: NRY
 
Intracranial Stenosis
Currently 2 devices have received approval for atherosclerotic disease from FDA through HDE process. This form of FDA approval is available for devices used to treat conditions with an incidence of 4,000 or less per year; FDA only requires data showing “probable safety and effectiveness.” Devices with their labeled indications are as follows:
 
    1. Neurolink System® (Guidant, Santa Clara, CA). “The Neurolink system is indicated for the treatment of patients with recurrent intracranial stroke attributable to atherosclerotic disease refractory to medical therapy in intracranial vessels ranging from 2.5 to 4.5 mm in diameter with ≥50% stenosis and that are accessible to the stent system.       
    2. Wingspan™ Stent System (Boston Scientific, Fremont, CA). “The Wingspan Stent System with Gateway PTA Balloon Catheter is indicated for use in improving cerebral artery lumen diameter in patients with intracranial atherosclerotic disease, refractory to medical therapy, in intracranial vessels with ≥50% stenosis that are accessible to the system.”
 
Intracranial Aneurysms
In 2011, FDA granted premarket approval to the Pipeline® Embolization Device (Covidien/ eV3 Neurovascular, Irvine, CA), an intracranial aneurysm flow diverter, for the endovascular treatment of adults (22 years of age or older) with large or giant wide-necked intracranial aneurysms in the internal carotid artery from the petrous to the superior hypophyseal segments (P100018) (FDA, 2011). Approval was based on the Pipeline for Uncoilable for Failed Aneurysms Study, a single-arm, open-label feasibility study that included 108 patients aged 30 to 75 years with unruptured large and giant wide-necked aneurysms (Becske, 2013).
 
Three stents have received FDA approval through the Humanitarian Device Exemption (HDE) program for treatment of intracranial aneurysms:
 
  1.  Neuroform™ Microdelivery Stent System (Stryker, Kalamazoo, MI). In 2002, based on a series of approximately 30 patients with 6-month follow-up, the Neuroform Microdelivery Stent System was approved (HDE) for use with embolic coils for treatment of wide-neck intracranial aneurysms that cannot be treated by surgical clipping (H020002).
 
2. Enterprise™ Vascular Reconstruction Device and Delivery System (Cordis Neurovascular Inc., Miami Lakes, FL) In 2007, based on a series of approximately 30 patients with 6-month follow-up, the Enterprise™ Vascular Reconstruction Device and Delivery was approved (HDE) for use with embolic coils for treatment of wide-neck, intracranial, saccular or fusiform aneurysms (H060001).
 
3. The Low-Profile Visualized Intraluminal Support Device (LVIS™ and LVIS™ Jr.) (MicroVention, Inc., Tustin, CA) in July 2014, received HDE approval in July 2014 (H130005) for use with embolic coils for the treatment of unruptured, wide neck (neck ≥ 4 mm or dome to neck ratio < 2), intracranial, saccular aneurysms arising from a parent vessel with a diameter ≥ 2.5 mm and ≤ 4.5 mm.
 
Coding
There are specific CPT codes for intracranial angioplasty and stent placement:
 
61630: Balloon angioplasty, intracranial (eg, atherosclerotic stenosis), percutaneous
61635: Transcatheter placement of intravascular stent(s), intracranial (eg, atherosclerotic stenosis), including balloon angioplasty, if performed
 
Codes 61630 and 61635 include all selective vascular catheterization of the target vascular family, all diagnostic imaging for arteriography of the target vascular family, and all related radiologic supervision and interpretation. If a diagnostic arteriogram confirmed the need for angioplasty or stent placement, those services are also included in 61630 and 61635.
If occlusion of a vascular malformation is performed as part of the treatment of an aneurysm, code 61624 would be used:
 
61624: Transcatheter permanent occlusion or embolization (eg, for tumor destruction, to achieve hemostasis, to occlude a vascular malformation), percutaneous, any method; central nervous system (intracranial, spinal cord).
 
Effective in 2016, there is a specific CPT code for mechanical thrombectomy:
 
61645: Percutaneous arterial transluminal mechanical thrombectomy and/or infusion for thrombolysis,
intracranial, any method, including diagnostic angiography, fluoroscopic guidance, catheter placement,
and intraprocedural pharmacological thrombolytic injection(s)  

Policy/
Coverage:
EFFECTIVE DECEMBER 2016
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage Criteria
 
Intracranial stent placement (CPT 61630, 61635) meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes as part of the endovascular treatment of intracranial aneurysms for patients when surgical treatment is not appropriate and standard endovascular techniques do not allow for complete isolation of the aneurysm, e.g., wide-neck aneurysm (4 mm or more) or sack-to-neck ratio less than 2:1.
 
Intracranial flow diverting stents with FDA approval (e.g.,Pipeline Embolization Device) (CPT 61624) for the treatment of intracranial aneurysms meets member benefit certificate primary coverage criteria as part of the endovascular treatment of intracranial aneurysms that are not amenable to surgical treatment or standard endovascular therapy provided the aneurysm is:
    • located in the internal carotid artery from the petrous to the superior hypophyseal segments; AND
    • a large or giant wide-necked intracranial aneurysm; AND,  
    • greater than or equal to 10 mm; AND
    • has a neck diameter greater than or equal to 4 mm.
 
Percutaneous transluminal angioplasty and stenting (CPT 61630, 61635) of intracranial and extracranial vertebral artery stenosis meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in patients meeting the following criteria:
 
    • Symptomatic patients (recurrent stroke or TIA) with stenosis refractory to medical therapy;  AND
    • Atherosclerosis with greater than or equal to 50% stenosis in an intracranial or extracranial vertebral artery that is accessible to the angioplasty/ stent system approved for marketing by the FDA for this specific indication.
 
Percutaneous transluminal intracerebral angioplasty/endovascular balloon dilatation of cerebral arteries for the treatment of vasospasm (CPT 61640, 61641, 61642) meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
The use of endovascular mechanical embolectomy with a device with FDA approval for the treatment of acute ischemic stroke (CPT 61645) may be considered medically necessary as part of the treatment of acute ischemic stroke for patients who meet all of the following criteria:
 
    • Have a demonstrated occlusion within the proximal intracranial anterior circulation (intracranial internal carotid artery, or M1 or M2 segments of the middle cerebral artery, or A1 or A2 segments of the anterior cerebral artery); AND
    • Can receive endovascular mechanical embolectomy within 12 hours of symptom onset; AND
    • Have evidence of substantial and clinically significant neurologic deficits (e.g., NIHSS score greater than or equal to 2); AND
    • Have evidence of salvageable brain tissue in the affected vascular territory (e.g., ASPECTS value of less than 7) AND
    • Have no evidence of intracranial hemorrhage or arterial dissection on computed tomography or magnetic resonance imaging.
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
 
Intracranial stent placement in the treatment of intracranial aneurysms in circumstances other than noted above does not meet member benefit certificate primary coverage that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, intracranial stent placement in the treatment of intracranial aneurysms in circumstances other than noted above is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Percutaneous transluminal angioplasty and stenting (CPT 61630, 61635) for the treatment of acute stroke does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, percutaneous transluminal angioplasty and stenting in the treatment of acute stroke are considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Percutaneous transluminal angioplasty and stenting for intracranial artery stenosis other than vertebral artery as indicated above does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.  This treatment is currently being studied in a clinical trial.
 
For members with contracts without primary coverage criteria, percutaneous transluminal angioplasty and stenting for intracranial artery stenosis other than vertebral artery as indicated above is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
The use of endovascular mechanical embolectomy for the treatment of acute ischemic stroke in circumstances other than noted above does not meet member benefit certificate primary coverage that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, the use of endovascular mechanical embolectomy for the treatment of acute ischemic stroke in circumstances other than noted above is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
EFFECTIVE PRIOR TO DECEMBER 2016
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage Criteria
 
Intracranial stent placement meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes as part of the endovascular treatment of intracranial aneurysms for patients when surgical treatment is not appropriate and standard endovascular techniques do not allow for complete isolation of the aneurysm, e.g., wide-neck aneurysm (4 mm or more) or sack-to-neck ratio less than 2:1.
 
Intracranial flow diverting stents with FDA approval (e.g.,Pipeline Embolization Device) for the treatment of intracranial aneurysms meets member benefit certificate primary coverage criteria as part of the endovascular treatment of intracranial aneurysms that are not amenable to surgical treatment or standard endovascular therapy provided the aneurysm is:
    • located in the internal carotid artery from the petrous to the superior hypophyseal segments; AND
    • a large or giant wide-necked intracranial aneurysm; AND,
    • greater than or equal to 10 mm; AND
    • has a neck diameter greater than or equal to 4 mm.
 
Percutaneous transluminal angioplasty and stenting of intracranial and extracranial vertebral artery stenosis meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in patients meeting the following criteria:
 
    • Symptomatic patients (recurrent stroke or TIA) with stenosis refractory to medical therapy;  AND
    • Atherosclerosis with greater than or equal to 50% stenosis in an intracranial or extracranial vertebral artery that is accessible to the angioplasty/ stent system approved for marketing by the FDA for this specific indication.
 
Percutaneous transluminal intracerebral angioplasty/endovascular balloon dilatation of cerebral arteries for the treatment of vasospasm meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
 
Intracranial stent placement in the treatment of intracranial aneurysms in circumstances other than noted above does not meet member benefit certificate primary coverage that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, intracranial stent placement in the treatment of intracranial aneurysms in circumstances other than noted above is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Endovascular interventions (mechanical embolectomy-thrombectomy, angioplasty, stenting) in the treatment of acute stroke do not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, endovascular interventions (mechanical embolectomy-thrombectomy, angioplasty, stenting) in the treatment of acute stroke are considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Percutaneous transluminal angioplasty and stenting for intracranial artery stenosis other than vertebral artery as indicated above does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.  This treatment is currently being studied in a clinical trial.
 
For members with contracts without primary coverage criteria, percutaneous transluminal angioplasty and stenting for intracranial artery stenosis other than vertebral artery as indicated above is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 

Rationale:
2015 Update
A literature search conducted through December 2014 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
Assessment of efficacy for therapeutic intervention involves a determination of whether the intervention improves health outcomes. The optimal study design for this purpose is a randomized controlled trial (RCT) that includes clinically relevant measures of health outcomes. Intermediate outcome measures, also known as surrogate outcome measures, may also be adequate if there is an established link between the intermediate outcome and true health outcomes. Nonrandomized comparative studies and uncontrolled studies can sometimes provide useful information on health outcomes, but are prone to biases such as noncomparability of treatment groups, placebo effect, and variable natural history of the condition.
 
RCTs Comparing Endovascular Therapies With Non-Interventional Care
From 2012 to 2014, results from 4 large RCTs comparing endovascular therapies with standard of care for acute ischemic stroke were published.
 
In 2014, Berkhermer et al reported initial results of the MR CLEAN trial (Multicenter Randomized Clinical trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands), an open-label, blinded end-point RCT with 500 subjects conducted at 16 centers in the Netherlands (Berkhemer, 2014). Eligible patients had acute ischemic stroke caused by an intracranial occlusion of the distal intracranial carotid artery, middle cerebral artery (M1 or M2), or anterior cerebral artery (A1 or A2), and a score of 2 or higher on the National Institutes of Health Stroke Scale (NIHSS). Initiation of intra-arterial treatment had to be possible within 6 hours of stroke onset. Patients were randomly assigned to standard stroke treatment (N=267; 53.4%) or intra-arterial treatment (N=233; 46.6%). Most patients in both groups (87.1% in the intervention group and 90.6% in the control group) received IV alteplase, at a median of 85 and 87 minutes after stroke onset, respectively. Patients in the intra-arterial group underwent arterial catheterization with a microcatheter to the level of the occlusion. Specific treatment options included delivery of a thrombolytic agent, mechanical thrombectomy, or both, at the discretion of the local interventionist. Intra-arterial thrombolytic agents were either alteplase or urokinase; mechanical treatment could involve thrombus retraction, aspiration, wire disruption, or use of a retrievable stent. Analysis was intention-to-treat. One control group patient received intra-arterial treatment, and 17 patients (7.3%) in the intervention group did not receive intra-arterial therapy, most commonly (N=8) due to clinical improvement before the start of the intervention. Among the 233 patients randomized to intra-arterial therapy, 195 (83.7%) received mechanical therapies, with retrievable stents used in 190 patients (81.5%) and other devices in 5 patients (2.1%). Twenty-four patients (10.3%) received additional intra-arterial thrombolytic agents. No intra-arterial intervention was performed following catheterization in 20 subjects because of intracranial artery stenosis, occlusion, tortuosity, or dissection (N=10), no clot or targetable clot visible for intra-arterial therapy (N=8), or other technical problems (N=2).
 
For the study’s primary outcome (modified Rankin scale score at 90 days), the median score was 3 (IQR 2-5) among intervention subjects, compared with a median score of 4 (IQR 3-5) among control subjects, with an unadjusted common odds ratio (OR) of 1.66 (95% confidence interval [CI] 1.21 to 2.28; favors intervention). Twenty-seven (11.6%) intervention subjects had a modified Rankin score of 0 or 1 at 90 days, compared with 16 (6.0%) control subjects (unadjusted OR 2.06; 95% CI 1.08 to 3.92). Follow-up computed tomography (CT) angiography was available for 187 control subjects, of whom 141 had no intracranial occlusion (75.4%), compared with 68/207 (32.9%) of control subjects with follow-up CT angiography available (unadjusted OR 6.27; 95% CI 4.03 to 9.74). The thirty-day mortality rate was 18.9% in the intervention group, compared with 18.4% in the control group (p=NS). Rates of serious adverse events during the 90-day follow up period did not differ significantly between groups (P=0.31)., Symptomatic intracerebral hemorrhage occurred in 7.7% of intervention subjects compared with 6.4% of control subjects, which was not a significant difference. However, intervention subjects were more likely to demonstrate a new ischemic stroke in different vascular territory (5.6% vs 0.4%; P<0.001).
 
In 2014, Tomsick et al published a subgroup analysis of the IMS-III trial focusing on subjects with intracranial internal carotid artery (ICA) or M1 occlusion (Tomsick, 2014). This analysis included 200 subjects, 65 with intracranial ICA and 135 with M1 segments as the target vessel for revascularization. Of these, at angiography, 82% had an arterial occlusive lesion (AOL) score of 2-3 and 76% had a modified Thrombolysis in Cerebral Infarction (mTICI) score of 2-3 (partial or full perfusion) after IV-tPA, which may have limited the potential benefit for device-related revascularization. Ninety-day Rankin scale scores were higher with higher mTICI scores: of 32 subjects with an mTICI score of 0, 3.1% had a modified Rankin scale score of 0-2 at 90 days, compared with 12.5%, 19.4%, 46.3%, and 80% for subjects with mTICI scores of 1 (total N=16), 2a (total N=67), 2b (total N=80) and 3 (N=5), respectively. To account for potential bias in the choice of endovascular therapy, propensity score analysis was used to compare subjects with different endovascular therapy modalities for the primary study outcomes. After propensity score adjustment, the authors found no clear differences in clinical or revascularization outcomes across revascularization methods, which included standard microcatheter thrombolysis (N=51), the Ekos catheter (N=14), the Merci retriever (N=77), the Penumbra device (N=39), the Solitaire device (N=4), and other methods (N=15).
 
In another IMS-III subgroup analysis, Demchuck et al evaluated the association between baseline CT or magnetic resonance (MR) angiography findings and outcomes among 306 (47% of 656) who had baseline CT or MR angiographic imaging available (Demchuk, 2014).  Ninety-two percent of those with angiography available had arterial occlusions demonstrated, 220 of which were proximal occlusions. Endovascular therapy group subjects with proximal occlusions had higher 24-hour recanalization rates than those with IV tPA only (84.3% of endovascular therapy subjects vs 56% of controls; P<0.001). However, no difference in the primary outcome, 90-day modified Rankin scale score of 0-2, was seen with proximal occlusions between groups (41.3% of endovascular therapy subjects vs 38% of controls; relative risk [RR] 1.07 [99% CI 0.67 to 1.70]).
 
Strengths of these 4 trials evaluating endovascular treatments for acute stroke include their randomized design and multisite recruitment.  A potential strength was that, in general, the endovascular intervention was left to the discretion of the treating physician, which could allow for greater generalizability; on the other hand, the variability in specific endovascular treatments used may make it difficult to draw conclusions about the efficacy of mechanical embolectomy. In the IMS III and SYNTHESIS Expansion trials, sizable proportions of the endovascular therapy groups did not receive an endovascular device: in IMS III, 138 of 334 of those who received endovascular therapy received intra-arterial tPA only (Broderick, 2013); in SYNTEHSIS Expansion 109 of 165 of those who received endovascular therapy received intra-arterial tPA with clot fragmentation with a guidewire but without device deployment (Ciccone, 2013). In contrast, in the most recently-published trial, MR CLEAN, most intervention-group subjects (83.7%) received an endovascular mechanical therapy. In addition, the 3 trials published in 2013 (Broderick et al, Kidwell et al, and Ciccone et al) all had relatively low utilization of the newer generation retrievable stents (Solitaire FR and Trevo devices), which may be relevant as several studies have demonstrated superiority of the newer generation retrievable stents compared with older neuroendovascular devices. Again, the Berkhemer et al (MR CLEAN) study differed in that a high proportion of intervention subjects received a retrievable stent (81.5%). For the IMS III trial, there was a longer time to endovascular procedure than in early trials of endovascular interventions; given evidence that longer time to reperfusion is associated with poorer outcomes, the delay in revascularization in the endovascular group may have contributed to worse clinical outcomes in that group. In contrast with IMS III and the Ciccone et al study, MR CLEAN required a radiologically proven intracranial occlusion for study eligibility.
 
 RCTs Comparing Different Endovascular Therapies
 
Assessment evaluated endovascular therapy for acute ischemic stroke in adults.19 The Assessment identified 5 multicenter RCTs meeting selection criteria, 3 of which compared endovascular treatment with standard stroke care (Broderick et al12, Ciccone et al (Ciccone, 2013), and Kidwell et al (Kidwell, 2013), and 2 of which newer and older endovascular treatments (Saver et al) (Saver, 2012) and Nogueira et al (Nogueira, 2012).The Assessment made the overall observations and conclusions:
 
“The 3 RCTs published in early 2013 concluded that endovascular treatment is no more effective than IV tPA in reducing disability among patients with acute ischemic stroke treated 3 to 8 hours after symptom onset. Although specific aspects of these trials have been criticized, we identified no RCTs that demonstrate endovascular treatments produce better health outcomes. Use of newer FDA-cleared endovascular devices was allowed. A major limitation in generalizing from these studies is that the number of patients treated with each of these newer devices was small. Therefore, as noted by critics of the trials, evidence on the newest devices may not substantively impact the overall outcomes. If the newer devices are more effective than the older ones, the results might be dominated by the performance of the less effective, older device(s).”
 
Urra et al conducted a prospective comparative study comparing endovascular therapy with IV thrombolysis alone in patients presenting with acute ischemic stroke due to large vessel occlusion and mild symptoms (NIHSS score ≤ 5) (Urra, 2014). The study included 78 patients, 34 treated with endovascular therapy and 44 treated medically. Compared with medical therapy alone, endovascular therapy was associated with higher rates of successful revascularization (91.2% vs 63.4%; P=0.006), but also higher rates of symptomatic intracranial hemorrhage (11.8% vs 0%; P=0.033). After adjusting for covariates, endovascular therapy was not significantly associated with modified Rankin scale score at 3 months.
 
Song et al compared treatment with stent-retriever devices and intra-arterial thrombolysis among 105 patients with acute ischemic stroke treated at a single institution (Song, 2014). Fifty-five patients were treated with the Solitaire stent-retriever device, while 50 patients were treated with intra-arterial thrombolysis with urokinase. After adjusting for occlusion site and rescue treatment, treatment with the stent-retriever was associated with successful reperfusion (82.0% vs 47.3%; adjusted OR 5.21; 95% CI 1.92 to 13.14) and likelihood of a favorable clinical outcome at 3 months (54.05 vs 43.6%; OR 3.40; 95% CI 1.31 to 8.84). Rates of mortality and symptomatic intracranial hemorrhage did not differ significantly between groups.
 
Liebeskind et al conducted a pooled analysis of MERCI and Multi MERCI subjects to assess whether lesion configuration (I, L, or T clots and functional lesions based on collateral flow patterns) was associated with clinical outcomes in ICA strokes treated with mechanical thrombectomy (Liebeskind, 2014). Seventy-two patients were included in the analysis, 32.6%, 31.9%, and 8.3% of whom received IV tPA, intra-arterial tPA, and other endovascular devices in addition to the MERCI, respectively. The presence of a functional T lesion, with insufficient collateral flow to ipsilateral anterior cerebral arteries, was associated with successful revascularization (TIMI grade 2-3; adjusted OR 0.25; 95% CI 0.09 to 0.69; P=0.007) and 90-day good clinical outcomes (adjusted OR 0.08; 95% CI 0.01 to 0.69; P=0.021).
 
Nonrandomized, Comparative Studies Evaluating Specific Endovascular Intervention(s)
Some nonrandomized comparative studies have compared the outcomes of different types of endovascular interventions.
 
Kappelhof et al published results of a systematic review and meta-analysis of studies comparing outcomes for mechanical therapy and intra-arterial thrombolysis for acute ischemic stroke due to ICA occlusion, with separate results reported for intracranial and extracranial occlusions (Kappelhof, 2015). The overall review included 32 studies, 6 of which (N=95) reported outcomes for intracranial occlusion treated by intra-arterial thrombolysis and 8 of which (N=115) reported outcomes for intracranial occlusion treated by mechanical thrombectomy. None of the recently-published RCTs of endovascular therapy were included in the review, which included studies published through July 2013 and specifically reporting outcomes for ICA occlusions. In the subset of studies reporting on intracranial occlusions, overall outcome rates were 55% recanalization, 12% symptomatic intracranial hemorrhage, 34% mortality, and 25% favorable outcome. Compared with intra-arterial fibrinolysis, mechanical thrombectomy was associated with a higher recanalization rate (69% vs 38%; P<0.001), a higher rate of favorable outcomes (34% vs 14%; P<0.001), with nonsignificantly different rates of death (29% vs 40%; P=0.085) and symptomatic intracranial hemorrhage (12.2% vs 11.7%; P=0.085).
 
For example, Turk et al conducted a retrospective, single-center review to compare clinical and cost-related outcomes for 3 endovascular interventions for acute stroke: the Penumbra system, stent retriever with local aspiration, and a “Direct Aspiration First Pass Technique” (ADAPT), which involves direct aspiration with a large bore catheter (Turk, 2014). Two hundred twenty-two patients underwent endovascular therapies for acute stroke during the study time period, 128 (58%) with the Penumbra system, 30 (13%) underwent with a stent retriever, and 64 (29%) underwent ADAPT. Recanalization rates (TICI 2b/3) were higher in the ADAPT group compared with the Penumbra group (95% vs 73%; P=0.0027), but no significant differences were seen across groups in 90-day modified Rankin scale scores.
 
Single-arm Studies Evaluating Endovascular Intervention in Basilar Artery Occlusion
In 2013, a number of several studies have reported noncomparative evaluations of endovascular therapies for acute basilar artery occlusion. Son et al reported outcomes for 31 subjects with acute basilar artery occlusion treated with mechanical thrombectomy with the Solitaire stent (N=13) or manual aspiration thrombectomy using the Penumbra reperfusion catheter (N=18) at a single center (son, 2014). Successful recanalization (TICI score ≥2b) did not differ between devices: 84.6% with the Solitaire stent compared with 100% with the Penumbra catheter (P=0.168); similarly, 3-month modified Rankin scale scores did not differ between the groups (3.6 with the Solitaire stent vs 3.2 with the Penumbra catheter; P=0.726).
 
The strongest evidence on the efficacy of endovascular mechanical embolectomy for acute ischemic stroke comes from 4 large RCTs published from 2013 to 2014. Three of these failed to demonstrate significant benefits from the use of endovascular mechanical embolectomy compared with usual therapy. These RCTs have some limitations, particularly related to relatively low use of embolectomy devices in general and of newer stent-retriever devices in particular, in their mechanical embolectomy groups. The most recently-published trial, MR CLEAN, addresses some of the limitations of the earlier trials, with a high proportion of intervention subjects receiving newer-generation stent-retriever devices and with inclusion criteria that required the presence of a proximal arterial occlusion. With the MR CLEAN results, there is now some RCT evidence that endovascular mechanical thrombectomy may improve outcomes of acute ischemic stroke. Results of additional ongoing randomized controlled trials of mechanical embolectomy will be needed to support or refute the MR CLEAN results. Based on the currently-available body of evidence, mechanical embolectomy for acute ischemic stroke is considered investigational. There is ongoing interest in the efficacy of stent-retriever devices in acute stroke and of endovascular interventions for basilar artery occlusion, which has a poor prognosis without treatment.
 
Endovascular Interventions for Symptomatic Intracranial Atherosclerotic Disease
 
Evidence about the role of endovascular stenting for treatment of symptomatic intracranial atherosclerotic disease consists of at least 2 RCTs, a number of nonrandomized comparative studies, and numerous single-arm series. The most clinically relevant RCTs, nonrandomized comparative studies, and systematic reviews are reviewed next. Since the publication of the RCT evidence, there continue to be single arm publications (i.e., with all subjects receiving endovascular stents) describing various aspects of stenting for intracranial stenosis, including utilization trends, (Tanweer, 2014), predictors of outcomes based on symptomatology, (Alexander, 2014), predictors of outcomes based on lesion morphology and arterial access (Miao, 2014) and clinical outcomes with the Wingspan system (Yu, 2014).
 
In 2013, Qureshi et al published results from another small RCT comparing angioplasty alone with angioplasty with a balloon-expanding stent among 18 subjects with moderate intracranial stenosis (stenosis ≥ 50%) with documented failure of medical treatment or severe stenosis (≥70%) with or without failure of medical treatment (Qureshi, 2013).  Technical success (<30% residual stenosis on immediate post-procedure angiography) occurred in 5/10 patients treated with angiography (9 randomized to angiography and 1 crossover from group randomized to stent placement) and 5/8 patients treated with stent placement. Rates of stroke or death were low in both groups: 1/10 in the angiography group and 0/8 in the stent placement group. This study suggests that angioplasty with stenting is feasible in patients with severe intracranial stenosis, but the small size and lack of statistical comparisons limit conclusions that can be drawn.
 
In 2014, Abuzinadah conducted a systematic review and meta-analysis of studies reporting the rates of stroke recurrence or death (the primary outcome) in symptomatic intracranial vertebrobasilar stenosis with medical or endovascular treatment (Abuzinadah, 2014). The authors identified 23 studies involving 592 medical treatment patients and 480 endovascular treatment patients. In pooled analysis, the stroke or death rate was 14.8 per 100 person-years (95% CI 9.5 to 20.1) in the medical therapy group and 8.9 per 100 person-years (95% CI 6.9 to 11.0) in the endovascular group (incidence rate ratio [IRR] 1.3; 95% CI 1.0 to 1.7). The stroke recurrence rate was 9.6 per 100 person-years (95% CI 5.1 to 14.1) in the medical group and 7.2 per 100 person-years (95% CI 5.5 to 9) in the endovascular group (IRR 1.1; 95% CI 0.8 to 1.5).
 
Stent-Assisted Treatment of Intracranial Aneurysms
Self-Expanding Stents
Three self-expanding stents, the Neuroform Microdelivery Stent System, the Enterprise Vascular Reconstruction Device and Delivery System, and the Low-Profile Visualized Intraluminal Support Device, have FDA approval through the HDE program for the endovascular treatment intracranial aneurysms. The literature search did not identify any randomized trials of self-expanding stent-assisted treatment of intracranial aneurysms compared with standard neurosurgical treatment, ie, surgical clipping or endovascular coils. The available evidence consists of single-arm case series, registry studies, nonrandomized comparative studies, and one systematic review of nonrandomized comparative studies
 
Systematic Reviews
In 2014, Hong et al reported results of a systematic review and meta-analysis of studies that compared stent-assisted coiling with coiling alone for the treatment of intracranial aneurysms (Hong, 2014). The authors included 10 retrospective cohort studies, ranging in size from 9 to 1109 patients. In pooled analysis, compared with coiling alone, stent-assisted coiling was associated with higher rates of progressive thrombosis (37.5% vs 19.4%; OR 2.75; 95% Ci 1.95 to 3.86; P<0.00001) and lower rates of recurrence (16.2% vs 34.4%; OR 0.35; 95% Ci 0.25 to 0.49; P<0.00001). Mortality was 9.1% for stent-assisted coiling, compared with 2.6% for coiling alone, although the difference was not statistically significant (OR 2.31; 95% CI 0.68 to 7.82; P=0.18). Similarly, permanent complication rates and thromboembolic complication rates were not significantly different between the two groups.
 
Hetts et al compared outcomes for patients treated with stent-assisted coiling with those treated with coiling alone for patients with unruptured intracranial aneurysms enrolled in the prospective, nonrandomized, multicenter Matrix and Platinum Science (MAPS) Trial, which was designed to compare bare-metal aneurysm coils and polymer-coated aneurysm coils (Hetts, 2014). One-hundred thirty-seven patients were included who received a stent-assisted coil, along with 224 patients treated with coiling alone. Patients treated with stent-assisted coiling more often had wide-neck aneurysms (62% vs 33%; P<0.0001) and had aneurysms with lower dome-to-neck ratio (1.3 vs 1.8; P<0.0001). Periprocedural serious adverse events occurred in 6.6% of those treated with stent-assisted-coiling, compared with 4.5% of those treated with coiling alone (P=0.039). At 1 year, ischemic strokes were more common in patients who received a stent-assisted coil than in patients who received a coil alone (8.8% vs 2.2%; P=0.005). However, in multivariable analysis, stent use did not independently predict ischemic stroke at 2 years (adjusted OR 1.1; P=0.94).
 
Liu et al compared outcomes for patients with posterior communicating artery aneurysms treated with stent-assisted coiling with those treated with coiling alone in a retrospective comparative study (Liu, 2014). A total of 291 coiling procedures were performed, including 56 aneurysms treated with a self-expandable stent. Complete aneurysm occlusion on initial angiography occurred in 41.1% of stent-assisted coiling patients compared with 35.3% of non-stented patients (statistical comparison not reported). At last follow up (mean 14.3 months for stent-assisted coiling and 13.2 months for non-stent patients), aneurysms recurred in 10.6% of stent-assisted coiling patients compared with 28.1% of non-stent patients (P=0.014). Procedural complications occurred in 10.7% of stent-assisted coiling patients compared with 11.5% of non-stent patients (stated to be nonsignificantly different).
 
In 2014, van Rooij et al reported outcomes for 550 consecutive patients treated with endovascular methods for intracranial aneurysms at a single European center from 2009 to 2013 (van Rooij, 2014). Endovascular treatments consisted of selective coiling in 445 (80.8%), stent-assisted coiling in 68 (12.4%), balloon-assisted coiling in 13 (2.4%), parent vessel occlusion in 12 (2.2%) and flow diverter treatment in 12 (2.2%). Among the 11 patients treated with flow divertors, 2 patients had ruptured dissecting aneurysms, 2 deaths occurred, 1 patient had permanent morbidity, and 2 aneurysms were not occluded at 30 months follow-up. Direct comparisons with outcomes from alternative treatments are not reported.
 
Kallmes, et al, published 2 meta-analyses (Kallmes, 2014) identifying 793 patients with 906 aneurysms, 311 were in the anterior ICA circulation and at least 10 mm, 349 of which were in the anterior circulation and less than 10 mm, 59 of which were in the posterior circulation, 179 of which were in a non-ICA anterior circulation location and less than 10 mm, and 10 of which had no aneurysm size specified. Overall neurologic morbidity and mortality was 8.4%, highest in the posterior circulation group and lowest in the ICA, less than 10 mm group (16.4% vs 4.8%; P=0.01. The overall spontaneous rupture rate was 0.6%, and the intracranial hemorrhage rate was 2.4%. Ischemic stroke rates were 4.7%, again highest in the posterior circulation group and lowest in the ICA, less than 10 mm group (7.3% vs 2.7%; P=0.16). Several additional a number of noncomparative studies evaluating flow-diverting stents in the treatment of aneurysms have been published. The largest cohort study identified was by Kallmes et al, who conducted a retrospective analysis of patients treated with the Pipeline device at 17 centers worldwide.
 
Ongoing and Unpublished Clinical Trials
Endovascular Interventions for Acute Ischemic Stroke
A query of the online site database ClinicalTrials.gov  in December 2014 identified a large number of studies are evaluating endovascular intracranial interventions for acute stroke. The following are RCTs that are evaluations of endovascular interventions compared with alternative treatment for acute stroke:
 
  • EndoVascular Treatment With Solitaire FR® vs. Best Medical Therapy in Acute Ischemic Stroke (RESILIENT) (NCT02216643) – This is a randomized, single-blinded trial to compare the Solitaire device with best medical therapy for patients with acute ischemic stroke in patients presenting up to 6 hours from stroke onset who are either ineligible for IV alteplase or have received IV alteplase therapy without recanalization. The primary outcome measure is modified Rankin scale score distribution. Enrollment is planned for 690 subjects, with an estimated study completion date of October 2017.
  •  Endovascular Acute Stroke Intervention Trial - the EASI Trial (NCT02157532) – This is a randomized, single-blinded trial to compare mechanical thrombectomy with best standard treatment for patients with acute ischemic stroke with onset of symptoms less than 5 hours prior to randomization or symptom/imaging mismatch. Enrollment is planned for 480 subjects; the planned study completion date is January 2018 with follow up through January 2020.
  • Endovascular Treatment for Small Core and Anterior Circulation Proximal Occlusion With Emphasis on Minimizing CT to Recanalization Times (ESCAPE) Trial (NCT01778335). This study randomly assigns patients with a confirmed symptomatic intracranial occlusion evaluated within 12 hours of last seen normal with a baseline NIHSS score greater than 5 at the time of randomization to an experimental group (endovascular mechanical thrombectomy or endovascular delivery of thrombolytic agent) or a control group (best medical therapy, including IV tPA if eligible). The primary outcome is proportion of patients who achieve a NIHSS score of 0 to 2 OR a Modified Rankin Scale score of 0 to 2 at 90 days. The study has been halted for efficacy at an enrollment of 316.
  • Endovascular Revascularization with Solitaire Device Versus Best Medical Therapy in Anterior Circulation Stroke within 8 Hours (REVASCAT) study (NCT01692379). This study randomly assigns patients with stroke from a large vessel occlusion seen within 8 hours to either embolectomy or standard medical therapy including IV recombinant tPA. The primary outcome measure is the modified Rankin Stroke scale at 90 days. Enrollment was planned for 690 patients, and estimated completion date was December 2015, but the study was terminated after interim analysis of 174 patients by its data safety and monitoring board.
 
Endovascular Interventions for Symptomatic Intracranial Atherosclerotic Disease
A query of the online site database ClinicalTrials.gov in December 2014 identified a large number of studies are evaluating endovascular intracranial interventions for atherosclerotic disease or aneurysms The following are RCTs that are evaluations of endovascular interventions compared with alternative treatment for symptomatic intracranial atherosclerotic disease:
 
  • China Angioplasty & Stenting for Symptomatic Intracranial Severe Stenosis (CASSISS): A Prospective Multicenter, Randomized Controlled Trial (NCT01763320). This study randomly assigns patients with symptomatic intracranial stenosis (TIA or nonsevere stroke within the past 12 months attributed to 70% to 99% stenosis of a major intracranial artery) to an intervention group (intracranial stenting) or a control group (medical therapy with aspirin and clopidogrel). The primary outcomes are the number of participants who suffer from Ischemic stroke, death, or cardiovascular events after enrollment or after any revascularization procedure of the qualifying lesion in the territory of the symptomatic intracranial artery within 30 days and between 30 days to 1 year after enrollment or any revascularization procedure of the qualifying lesion. Enrollment is planned for 380 patients, and the estimated completion date is listed as December 2017.
 Phase III Study of Pharos Vitesse Neurovascular Stent System Compared to Best Medical Therapy for the Treatment of Ischemic Disease (NCT00816166). This study randomly assigns patients with TIA or stroke attributable to a neurovascular stenosis (70%-99%) within the prior 30 days to an experimental group (PHAROS neurovascular stent placement with medical therapy) or a control group (medical therapy). The primary effectiveness end point is stroke or TIA in the same territory as the presenting event within 12 months of enrollment. Enrollment is planned for 250 patients, and the estimated completion date is listed as June 2014, but study has been terminated.
 
2016 Update
A literature search conducted through October 2016 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
Endovascular Interventions for Anterior Circulation Acute Ischemic Strokes
The evidence review focuses on the available RCTs and other comparative studies.
 
Systematic Reviews
Multiple systematic reviews and meta-analyses of RCTs evaluating endovascular therapy for acute stroke have been published, with varying inclusion criteria. The most relevant of the systematic reviews include the results of a series of RCTs published from 2014 to 2015 comparing endovascular therapies with standard care; these are the focus of this review. Some systematic reviews have focused only on mechanical embolectomy, while others have evaluated endovascular therapies more broadly.
 
In 2015, Badhiwala and colleagues reported results of a systematic review and meta-analysis of RCTs evaluating mechanical embolectomy after acute ischemic stroke (Badhiwala, 2015). Eligible studies were RCTs comparing endovascular therapy with standard care, including the use of intravenous tPA, in adult participants with acute stroke. Eight trials were included (Ciccone, 2013;  Kidwell, 2013;  Broderick, 2013;  Berkhemer, 2014; Goyal, 2015; Campbell, 2015;  Saver, 2012; and Jovin, 2015), with a total of 2423 patients. (These specific RCTs are described individually below). Studies were assessed as having low risk of bias overall with the Cochrane Collaboration’s tool. In a meta-analysis, the use of endovascular intervention lead to lead to proportional treatment benefit across modified Rankin scale (mRS) scores (odds ratio [OR], 1.56; 95% confidence interval [CI], 1.14 to 2.13; p=0.005). Patients treated with endovascular intervention were more likely than standard care patients to have functional independence at 90 days (44.6% for endovascular treatment [95% CI, 36.6% to 52.8%]; 31.8% for standard treatment [95% CI, 24.6% to 40.0%]), with an associated absolute risk difference of 12.0% (95% CI, 3.8% to 20.3%; odds ratio [OR], 1.71; 95% CI, 1.18 to 2.49; p=0.005). However, there was significant heterogeneity (I2=75.4%) in the analysis of functional improvement outcomes. The authors conducted a number of sensitivity analyses around predictors of functional outcomes, and found that the following factors were associated with functional outcomes:
  • Use of angiographic imaging confirming proximal arterial occlusion (OR=2.24; 95% CI, 1.72 to 2.9; p<0.001 for interaction).
  • Use of intravenous tPA and endovascular therapy (OR=2.07; 95% CI, 1.46 to 2.92; p=0.018 for interaction).
  • Use of stent retriever for mechanical thrombectomy (OR=2.39; 95% CI, 1.88 to 3.04; p<0.001 for interaction).
 
There were no significant differences between endovascular intervention group and standard care group patients in rates of symptomatic intracranial hemorrhage or death at 90 days.
 
In a meta-analysis including the same 8 trials included in the Badhiwala and colleagues study, Chen and colleagues (Chen, 2015) reported a similar odds ratio for 90 day functional independence as Badhiwala.
 
Hong and colleagues conducted a systematic review and meta-analysis of RCTs comparing endovascular recanalization therapy with standard care in acute ischemic stroke (Hong, 2015). This analysis included 15 RCTs with a total of 2,899 patients, 1575 randomized to endovascular recanalization arms and 1324 to control arms. In addition to the 8 trials which compared mechanical embolectomy with standard care (Ciccone, 2013;  Kidwell, 2013;  Broderick, 2013;  Berkhemer, 2014; Goyal, 2015; Campbell, 2015;  Saver, 2012; and Jovin, 2015),this review also included 2 trials evaluating intra-arterial pro-urokinase, 3 trials evaluating intra-arterial urokinase, 1 evaluating intra-arterial with intravenous tPA, and 1 evaluating intra-arterial tPA with mechanical thrombectomy. In a random-effects model including all trials, endovascular recanalization was associated with greater proportions of patients with mRS of 0-2 (43.3% vs 31.9%, OR 1.79, 95% CI 1.34 to 2.4, P<0.001). For safety outcomes, when all trials were included, rates of symptomatic intracranial hemorrhage (SICH) were higher in endovascular recanalization arms, although the between group difference was not statistically significant (5.8% vs 4.6%, OR 1.19, 95% CI 0.83 to 1.69, P=0.345).
 
In another systematic review and meta-analysis, Kennedy and colleagues compared local mechanical and/or pharmacologic endovascular therapy, with or without intravenous thrombolysis, with standard-care control that included intravenous thrombolysis when appropriate.23 Eleven RCTs were included, the 8 trials comparing mechanical embolectomy with standard care (Ciccone, 2013;  Kidwell, 2013;  Broderick, 2013;  Berkhemer, 2014; Goyal, 2015; Campbell, 2015;  Saver, 2012; and Jovin, 2015), along with 2 trials comparing intra-arterial tPA with intravenous tPA alone, one of which was very small (n=7), and one evaluating intra-arterial tPA with mechanical thrombectomy. In a meta-analysis of all trials, patients in the local endovascular therapy groups had higher rates of functional independence than those treated with standard care (OR 1.78, 95% CI 1.262 to 2.51, P<0.001). In subanalyses limited to trials that used imaging selection, that used stent-retriever devices in at least half of cases, or in which intravenous tPA was used in conjunction with endovascular therapy as appropriate, the use of local endovascular therapy remained significantly associated with higher rates of functional independence, with stronger effect sizes than in the overall analysis. However, in a subanalysis limited to trials in which endovascular arm patients did not receive intravenous tPA, there was no significant between-group difference in 90-day functional independence (OR 1.45, 95% CI 0.597 to 3.54, P>0.05).
 
Given the disproportionate benefit associated with stent retriever use in subanalyses of RCTs, there has been some focus on the specific efficacy of stent retrievers for acute stroke.
 
Bush and colleagues conducted a systematic review and meta-analysis of RCTs using predominantly stent retriever devices for acute stroke treatment (Bush, 2016). Trials that compared endovascular therapy with stent retrievers with medical management (defined as intravenous tPA unless it was contraindicated) were included. However, it is not specified how the authors defined a threshold to determine whether stent retrievers were “predominantly” used. The analysis included 5 trials (Berkhemer, 2014; Goyal, 2015; Campbell, 2015; Saver, 2012; and Jovin, 2015) with a total of 1287 patients. In pooled analysis for the review’s primary outcome, mRS at 90 days, patients randomized to endovascular therapy had an OR for more favorable mRS of 2.2 (95% CI, 1.66 to 2.98; p<0.001; I2=46.38%). Similar to the findings from the Badhiwala metaanalysis, there were no significant between-group differences in 90-day mortality rates or rates of symptomatic intracranial hemorrhage.
 
Similarly, Grech and colleagues conducted a systematic review and meta-analysis of RCTs comparing stent retriever devices (trials in which second-generation thrombectomy devices comprised at least 80% of thrombectomy devices used) with intravenous thrombolysis in acute stroke.25 The systematic review included the same 5 trials as the Bush et al review (Berkhemer, 2014; Goyal, 2015; Campbell, 2015; Saver, 2012; and Jovin, 2015).  In pooled analysis, the OR for functional independence at 90 days between thrombectomy and intravenous thrombolysis groups was 2.4 (46.1% for thrombectomy vs 26.5% for intravenous thrombolysis; 90% CI for OR: 1.89 to 3.05, P<0.001).
 
The results of the Bush et al and Grech et al systematic reviews were supported by a third systematic review of RCTs comparing stent retriever devices with standard care reported by Marmagkioli and colleagues (Marmagkiolis, 2015; Touma, 2016).
 
Zheng and colleagues conducted a systematic review and meta-analysis of RCTs comparing endovascular therapy with intravenous tPA, with analysis stratified by whether computed tomography angiography (CTA) was used to select patients for endovascular therapy (Zhen, 2015). The review included 7 RCTs with 2217 patients (Berkhemer, 2014; Broderick, 2013; Ciccone, 2013; Kidwell, 2013, Campbell, 2015; and Goyal, 2015), of which 4 used CTA to select patients. Endovascular therapy was associated with functional independence at 90 days in patients who underwent CTA-based selection (RR=1.75; 95% CI, 1.48 to 2.06; I2=0.05%), but not in patients who did not undergo CTA-based selection (RR=0.99; 05% CI, 0.85 to 1.14; I2=0.0%). All-cause mortality was not significantly associated with 90-day mortality, regardless of whether patients were selected with CTA.
 
A group of investigators have formed the Virtual International Stroke Trials Archive (VISTA)-Thrombectomy and Tissue Plasminogen Activator (TREAT) collaboration to develop protocols for patient level meta-analyses of pooled data from RCTs in which at least 85% of treated cases are treated with newer devices (direct aspiration catheters or stent retrievers) (Maclsaac, 2015).
 
Randomized Controlled Trials
 
RCTs Comparing Endovascular Therapies with Non-interventional Care
From 2012 to 2015, results from 8 large RCTs comparing endovascular therapies with standard of care for acute ischemic stroke were published. Five prospective, open-label, blinded end point (PROBE design) RCTs comparing endovascular therapy with standard care in the treatment of acute stroke were published from 2014 to 2015 and are the focus of this discussion. A high-level overview of the major RCTs follows, with a summary of results in Table 2. Subsequently in this section, the trials are described in more detail.
 
Although the RCTs report on a number of outcomes results pertaining to 3 specific outcomes are the focus here: the proportion of patients with 90-day modified Rankin scale (mRS) score of 0-2, short-term mortality rate, and rates of symptomatic intracranial hemorrhage (sICH). The primary goal of rapid revascularization in acute stroke is to reduce rates of significant disability; mRS scores of 0-2 correspond to functional independence, so represent a clinically useful measure of disability. Prior studies of endovascular therapy and thrombolytic therapy for acute stroke have been associated with increased risks of sICH, so this is another important safety-related outcome to evaluate.
 
There were 8 randomized controlled trials (RCTs) with a total of 2423 patients (range, 70-656) which compared endovascular mechanical embolectomy with standard care for acute ischemic stroke. In two studies, the population and intervention delivered were not consistent with the target population and intervention; the remaining 6 studies with the populations and interventions of interest are the focus of this discussion. The most clinically-relevant and consistently reported finding was a comparison between treatment and control groups in the proportion of patients with a mRS score at 90 days of 0-2. Among the 6 studies reporting on the population and intervention of interest, all provide some information on the proportion of patients with 90-day mRS of 0-2. Across the studies, the absolute difference between treatment and control groups in proportion of patients with 90-day functional independence ranged from 1.55% to 25%. With one exception (MR Rescue [Kidwell et al]), all of the studies reported a statistically significant improvement in the proportion of patients with functional independence at 90 days, with odds ratios ranging from 1.7 to 3.8. Among the 6 studies reporting on the populations and interventions of interest, mortality rates and sICH rates did not differ significantly between study groups. It is not possible to draw conclusions about the safety or harm of the procedure from this finding; the lack of significant difference may be due to inadequate sample sizes.
 
RCTs Comparing Different Endovascular Therapies
Saposnik  and colleagues evaluated the added benefit added by stent retrievers to intravenous tPA using pooled patient-level data from the SWIFT study (Saposnik, 2015) and the STAR trial, a prospective, single-arm trial of the solitaire device (Pereira, 2013), along with data from the NINDS tPA Stroke Study, a RCT evaluating intravenous tPA. Of 915 patients included in the pooled analysis, 312 were treated with placebo, 312 with intravenous tPA, 106 with stent retrievers alone, and 160 with intravenous tPA and stent retrievers. The authors used a shift analysis which used a proportional odds model to evaluate the association between treatment and each of the 7 mRS categories. The use of stent retrievers (alone or with tPA) was associated with a higher probability of functional Independence (mRS 0-2) at 90 days: 41% of those treated with tPA alone, 69.8% of those treated with stent retrievers, and 72.8% of those treated with stent retrievers and tPA had functional independence at 90 days.
 
Noncomparative Studies
Huo and colleagues reported outcomes for 36 consecutive patients with acute basilar artery occlusion treated with the Solitaire stent (Huo, 2015) Recanalization (TICI grade ≥ 2b) was successful in 94.4% of patients. However, mortality at 90 days was high (30.56%). Of note, 30 (83.3%) patients had stenosis in the occluded artery and 25 patients (69.4% of all patients in the series) also underwent angioplasty.
 
Systematic Reviews
In 2015, Ryu and colleagues conducted a systematic review of studies reporting complications after stent-assisted coiling of ruptured intracranial aneurysms, with a focus on the association of complications with anti-platelet therapy (Ryu, 2015).The review included 33 studies, 3 of which were prospective and the remaining 30 retrospective (total N=1090 patients). In pooled analysis, thromboembolic complications occurred in 108 patients (event rate, 11.2%; 95% CI, 9.2% to 13.6%). Intra-procedural hemorrhage occurred in 46 (event rate, 5.4%; 95% CI, 4.1% to 7.1%).
 
Nonrandomized Comparative Studies
Consoli and colleagues compared stent-assisted coiling with balloon-assisted coiling in patients with unruptured wide-necked intracranial aneurysms treated at a single center (Consoli, 2016). The study included 268 patients with 286 aneurysms, 117 (122 aneurysms) of whom were treated with stent-assisted coiling and 151 (164 aneurysms) of whom were treated with balloon-assisted coiling. At discharge, 97.9% and 97.3% of those in the balloon-assisted and stent-assisted groups, respectively, had mRS of 0-1 (statistical comparison not reported). After 6 months, 97.9% and 98% of those in the balloon-assisted and stent-assisted groups, respectively, had mRS of 0-1, while mortality rates were 2.6% and 1.7% in the balloon-assisted and stent assisted groups, respectively (statistical comparisons not reported). At 6 months, aneurysm recurrence rates were 11.1% and 5.8% in the balloon-assisted and stent-assisted groups, respectively. In multivariable analysis, the use of stent-assisted coiling was significantly associated with complete occlusion at the end of the procedure (regression coefficient not reported; p=0.024) and complete occlusion after 6 months (regression coefficient not reported; p=0.05).
 
Comparison between Endovascular Devices for Intracranial Aneurysms
Nonrandomized studies, which have been summarized in a systematic review by King and colleagues report comparisons between devices used for stent-assisted coiling of intracranial aneurysms.
 
King and colleagues reviewed published studies reporting on stent-assisted coiling with the Neuroform and Enterprise systems to compare outcomes between the devices (King, 2015).The analysis included 47 studies with a total of 4039 patients (4238 aneurysms; 2111 and 2127 treated with the Neuroform and Enterprise systems, respectively). Most studies were retrospective (81%). Compared with those treated with the Enterprise system, patients treated with the Neuroform system were more likely to have deployment failure (2.3% vs 0.2%, p<0.001), had a higher mortality rate (2.8% vs 1.8%, p=0.04), were less likely to have 100% aneurysm occlusion at last follow up (61.1% vs 74.7%,p<0.001), and were more likely to have recanalization (13.9% vs 10.6%, p=0.02). However, conclusions that can be drawn from these findings are limited by the potential for bias in the underlying studies and between-study heterogeneity.
 
Single-Arm Series
In another relatively large study, Lee et al reported on 1038 patients treated with endovascular coiling, 296 of whom underwent stent-assisted coiling, with a focus on predictors of procedural rupture.121 Three cases of procedural rupture occurred among patients treated with stent-assisted coiling.
 
Other representative non-comparative studies in which at least some patients are treated with devices commercially available in the United States are summarized in Table 2. Interpretation of these studies is limited by potential selection bias and no comparison group. In general, these series demonstrate high rates of technical success of stent deployment with high rates of aneurysm occlusion; however, variable complication rates, particularly related to thromboembolic events were observed.
 
Flow-Diverting Stents for Intracranial Aneurysms
Nonrandomized Comparative Studies
Zhou and colleagues reported results of a systematic review of studies comparing flow-diverting devices with endovascular coiling for intracranial aneurysms which included 9 retrospective comparative studies with a total of 863 subjects (Zhou, 2015). This review included studies with ruptured or unruptured aneurysms. Across the 9 studies, 305 patients were treated with flow-diverting devices, 558 with coil embolization therapy, and 324 with stent-assisted coiling alone. In pooled analysis, the use of flow diverting devices was associated with a significantly higher complete occlusion rate when compared with coil embolization therapy (OR 3.13, 95% CI 2.11 to 4.65, I2=18%) or with stent-assisted coiling (OR 2.08, 95% CI 1.34 to 3.24, I2=0%). Rates of overall morbidity were not significantly different between flow diverting device- and coil embolization therapy-treated patients, or between flow diverting device- and stent-assisted coiling-treated patients.
 
Single-Arm Series
Multiple noncomparative studies have reported outcomes from flow-diverting stent-assisted treatment of intracranial aneurysms since the introduction of the Pipeline endovascular device. These studies have been summarized in several systematic reviews and meta-analyses. The largest systematic review identified (reported by Briganti and colleagues reviewed 18 studies published from 2009 to 2014 with 1483 patients (1704 aneurysms) (Briganti, 2015). Most (87.5%) treated aneurysms were in the anterior circulation and most (87.5%) were saccular in morphology. In the 17 studies reporting procedural complications, mean incidence was 8.3% (range, 0%-23.1%). Permanent morbidity occurred in a mean 3.5% of patients (range: 0%-15%), while the mean mortality rate was 3.4% (range, 0.5%-8%). Across the 18 studies, aneurysms were completely occluded in a mean 81.5% of cases (range, 69%-100%).
 
Guedon and colleagues reported on late ischemic complications after flow diverting stent placement (Guedon, 2016.  Among 86 patients treated at a single institution, angiographic follow up was available to a mean 15.7 months ([SD=11.8 months; median, 13 months; range, 8-21 months) and clinical follow-up was available to a mean 16.9 months (SD=12.9 months; median, 14 months; range 10-22 months). Five (5.8%) patients developed ischemic complications.
 
2018 Update
A literature search conducted using the MEDLINE database through February 2018  did not reveal any new information that would prompt a change in the coverage statement. The following is a summary of the key identified literature.
 
DAWN Trial. Nogueira et al reported on results of the DAWN trial, a multicenter, Bayesian, adaptive, open-label RCT with blinded outcome assessment sponsored by Stryker Neurovascular (Nogueira, 2018).  DAWN included patients who had last been known to be well 6 to 24 hours earlier and who had a mismatch between the severity of the clinical deficit and the infarct volume. DAWN was conducted at 26 sites in the United States, Canada, Europe, and Australia from September 2014 through February 2017. Patients were assigned to thrombectomy plus standard care (n=107) or standard care alone (n=99). Very few patients were treated with IV tPA because patients were generally enrolled after the accepted window of time in which IV tPA is administered. The adaptive trial was originally designed for a sample size ranging from 150 to 500 patients but was stopped early due to efficacy. The mean age was 70 years, and the median NIHSS score was 17. Approximately 55% of the patients had a “wake-up” stroke. The proportion of patients with functional independence (mRS score ≤2) at 90 days was 49% in the thrombectomy group and 13% in the standard care group (adjusted difference, 33%; 95% credible interval, 24% to 44%; posterior probability of superiority, >0.999). The proportion of patients with symptomatic intracranial hemorrhage at 24 hours was 6% in the thrombectomy group and 3% in the standard care group (p=0.50). The 90-day mortality rate was similar between groups (19% vs 18%, respectively; p=1.00).
 
Noguiera et al compared use of the Penumbra 3-D stent retriever and an aspiration-based mechanical thrombectomy device with the Penumbra aspiration system alone in 198 patients from 25 North American sites enrolled from May 2012 through November 2015 (Noguiera, 2018). Eligible patients had large vessel intracranial occlusion acute ischemic stroke with an NIHSS score of at least 8 within 8 hours of onset. The primary effectiveness outcome was the rate of a mTICI score of 2 to 3, with a 15% noninferiority margin. One hundred ninety patients were included in the primary analysis. Eighty-two (87%) of 94 patients in the 3-D stent retriever group had a mTICI score of 2 to 3 compared with 79 (82%) of 96 in the aspiration alone group (difference, 4.9%; 90% CI, -3.6% to 13.5%). The incidence of the device- and procedure-related serious adverse events within 24 hours of the procedure was 4 (4%) of 98 patients in the 3-D stent retriever group and 5 (5%) of 100 in the aspiration alone group.
 
No randomized trials evaluating intracranial aneurysms were identified comparing flow-diverting stent treatment with standard neurosurgical treatment (ie, surgical clipping or endovascular coils) from the time of FDA approval until 2017 (Raymond, 2017).
 
PRACTICE GUIDELINES AND POSITION STATEMENTS
American Heart Association and American Stroke Association
The American Heart Association and the American Stroke Association (2018) published joint guidelines on the early management of patients with acute ischemic stroke (Powers, 2018). These guidelines included several recommendations relevant to the use of endovascular therapies for acute stroke.

CPT/HCPCS:
36215Selective catheter placement, arterial system; each first order thoracic or brachiocephalic branch, within a vascular family
36216Selective catheter placement, arterial system; initial second order thoracic or brachiocephalic branch, within a vascular family
36217Selective catheter placement, arterial system; initial third order or more selective thoracic or brachiocephalic branch, within a vascular family
36218Selective catheter placement, arterial system; additional second order, third order, and beyond, thoracic or brachiocephalic branch, within a vascular family (List in addition to code for initial second or third order vessel as appropriate)
61624Transcatheter permanent occlusion or embolization (eg, for tumor destruction, to achieve hemostasis, to occlude a vascular malformation), percutaneous, any method; central nervous system (intracranial, spinal cord)
61630Balloon angioplasty, intracranial (eg, atherosclerotic stenosis), percutaneous
61635Transcatheter placement of intravascular stent(s), intracranial (eg, atherosclerotic stenosis), including balloon angioplasty, if performed
61640Balloon dilatation of intracranial vasospasm, percutaneous; initial vessel
61641Balloon dilatation of intracranial vasospasm, percutaneous; each additional vessel in same vascular family (List separately in addition to code for primary procedure)
61642Balloon dilatation of intracranial vasospasm, percutaneous; each additional vessel in different vascular family (List separately in addition to code for primary procedure)
61645Percutaneous arterial transluminal mechanical thrombectomy and/or infusion for thrombolysis, intracranial, any method, including diagnostic angiography, fluoroscopic guidance, catheter placement, and intraprocedural pharmacological thrombolytic injection(s)
61650Endovascular intracranial prolonged administration of pharmacologic agent(s) other than for thrombolysis, arterial, including catheter placement, diagnostic angiography, and imaging guidance; initial vascular territory
61651Endovascular intracranial prolonged administration of pharmacologic agent(s) other than for thrombolysis, arterial, including catheter placement, diagnostic angiography, and imaging guidance; each additional vascular territory (List separately in addition to code for primary procedure)

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