Computed Tomography Perfusion Imaging of the Brain

POLICY NUMBER

A.6.01.49

DESCRIPTION

Computed tomography perfusion (CTP) imaging provides an assessment of cerebral blood flow that may help identify ischemic regions of the brain. This technology is proposed to aid treatment decisions in patients being evaluated for acute ischemic stroke, subarachnoid hemorrhage, cerebral vasospasm, brain tumors, and head trauma.

Acute Stroke

In the United States (U.S.), approximately 795,000 individuals experience a stroke annually, making stroke the fifth most common cause of death in the U.S. Black individuals experience a 2-fold greater risk of first-ever stroke compared to White individuals, and stroke incidence can differ according to geographic region. Additionally, the Hispanic population has experienced an increase in stroke incidence since 2013. The quality of stroke care in minority individuals is impacted by several factors that lead to disparities, most notably being overall access to quality health care. A systematic review found racial disparities in emergency medical service utilization and time to treatment. White patients were estimated to use emergency medical services at a greater rate (59.8%) compared to African American (55.6%), Asian (54.7%), and Hispanic patients (53.2%). A greater proportion of White patients (37.4%) were estimated to arrive within 3 hours from onset of stroke symptoms compared to African American (26.0%) and Hispanic (28.9%) patients. Additionally, a greater proportion of White patients (2.8%) were estimated to receive tissue plasminogen activator (tPA) compared with African American (2.3%), Hispanic (2.6%), and Asian (2.3%) patients. Another recent retrospective study found that among 37,790 patients in the Veterans Health Administration system, absolute risk of 30-day mortality after intracerebral hemorrhage was 3.2% higher for Black patients and, after subarachnoid hemorrhage, was 10.3% higher for Hispanic patients compared with White patients.

The goal of acute stroke thrombolytic treatment is to rescue the ischemic penumbra, an area of the brain that surrounds the infarct core and is hypoperfused but does not die quickly. Multimodal computed tomography (CT) and magnetic resonance imaging (MRI) can be used to assess the cerebral parenchyma, vasculature, and tissue viability in the acute ischemic stroke setting and are used to detect ischemic tissue, and exclude hemorrhage and other conditions that mimic acute cerebral ischemia.

Non-contrast CT is used to rule out intracranial hemorrhage, tumor, or infection. Diffusion-weighted MRI is used to identify acute infarction, and a gradient-recalled echo sequence is used to exclude intracerebral hemorrhage.

Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are used to evaluate intra- and extracranial vasculature to detect the vascular occlusion and potentially guide therapy (e.g., intravenous thrombolysis or mechanical thrombectomy).

The approved thrombolytic therapy, an intravenous tissue plasminogen activator, requires only a non-contrast CT scan to exclude the presence of hemorrhage (a contraindication to the use of the drug). Current guidelines are to administer tissue plasminogen activator within the first 3 hours after an ischemic event, preceded by a CT scan. Many patients, however, do not present to the emergency department within the 3-hour window, and thrombolysis carries a risk of intracranial hemorrhage. Thus, more sophisticated imaging may be needed to select the proper use of intra-arterial thrombolysis or mechanical thrombectomy in patients who present more than 3 hours after an ischemic stroke. Perfusion imaging is also being evaluated in the management of other neurologic conditions, such as subarachnoid hemorrhage and head trauma.

The potential utility of perfusion imaging for acute stroke is as follows:

• Identification of brain regions with extremely low cerebral blood flow, which represent the core;

• Identification of patients with at-risk brain regions (acutely ischemic but viable penumbra) that may be salvageable with successful intra-arterial thrombolysis beyond the standard 3-hour window;

• Triage of patients with at-risk brain regions to other available therapies, such as induced hypertension or mechanical clot retrieval;

• Decisions regarding intensive monitoring of patients with large, abnormally perfused brain regions;

• Biologically-based management of patients who awaken with a stroke for which the precise time of onset is unknown.

Additional potential uses of CT perfusion in acute stroke may include the following:

• Detection and differential diagnosis (eg, excluding stroke mimics such as transient ischemic attack, complex migraine, seizure, conversion disorders, hypoglycemia, brain tumors),

• Determination of stroke subtype,

• Determination of stroke extent, including additional vascular territories at risk,

• Identification of patients at high early risk for stroke following a transient ischemic attack,

• Determining the need for blood pressure management,

• Establishing prognosis.

Similar information can be provided by CT and MRI regarding infarct core and penumbra. However, multimodal CT has a short protocol time (5 to 6 minutes), and because it can be performed with any modern CT equipment, is more widely available in the emergency department setting. Computed tomography perfusion imaging is performed by capturing images as an iodinated contrast agent bolus passes through the cerebral circulation and accumulates in the cerebral tissues. Older perfusion methodologies such as single-photon emission CT and xenon-enhanced CT scanning use a diffusible tracer. The quantitative perfusion parameters are calculated from density changes for each pixel over time with the commercially available deconvolution-based software, in which cerebral blood flow is equal to regional cerebral blood volume divided by mean transit time. Computed tomography angiography and CT perfusion imaging require ionizing radiation and iodinated contrast. It is estimated that typical CTP imaging deposits a slightly greater radiation dose than a routine unenhanced head CT (approximately 3.3 mSv).

Subarachnoid Hemorrhage and Cerebral Vasospasm

Cerebral vasospasm is a major cause of morbidity and mortality following aneurysmal subarachnoid hemorrhage in patients who survive the initial hemorrhage and can be seen in about two-thirds of patients with aneurysmal subarachnoid hemorrhage. The typical onset of cerebral vasospasm occurs 3 to 5 days after hemorrhage, with maximal narrowing on digital subtraction angiography at 5 to 14 days. Currently, the diagnosis of vasospasm and management decisions rely on clinical examination, transcranial Doppler sonography, and digital subtraction angiography. Although symptomatic vasospasm affects 20% to 30% of patients with aneurysmal subarachnoid hemorrhage, not all patients with angiographic vasospasm manifest clinical symptoms, and the symptoms can be nonspecific. Also, patients do not always have both clinical and imaging findings of vasospasm. Due to these limitations, more accurate and reliable methods to detect cerebral vasospasm are being investigated.

Brain Tumors

The current standard for tumor grading is histopathologic assessment of tissue. Limitations of histologic assessment include sampling error due to regional heterogeneity and interobserver variation. These limitations can result in inaccurate classification and grading of gliomas. Because malignant brain tumors are characterized by neovascularity and increased angiogenic activity, perfusion imaging has been proposed as a method to assess tumor grade and prognosis. Also, perfusion imaging can be repeated and may help to assess the evolution of tumors and the treatment response. Traditionally, perfusion imaging of brain tumors has been performed with MRI, which can estimate tumor blood volume, blood flow, and permeability. More recently, CTP imaging has been investigated for glioma grading. Potential advantages, compared with magnetic resonance perfusion, include the wider availability, faster scanning times, and lower cost. Computed tomography perfusion imaging may also be used to distinguish recurrent tumor from radiation necrosis.

Several post-processing software packages (e.g., Siemens’ syngo® Perfusion-CT, GE Healthcare’s CT Perfusion 4, Philips Medical System’s Brain Perfusion Option) have been cleared for marketing by the U.S. Food and Drug Administration for use with a CT system to perform perfusion imaging. The software is being distributed with new CT scanners.

POLICY

Computed tomography perfusion (CTP) imaging may be considered medically necessary to select individuals with anterior large-vessel stroke for mechanical embolectomy.

Computed tomography perfusion imaging of the brain is considered investigational for all other indications.

POLICY EXCEPTIONS

Federal Employee Program (FEP) may dictate that all FDA-approved devices, drugs or biologics may not be considered investigational and thus these devices may be assessed only on the basis of their medical necessity.

POLICY GUIDELINES

The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.

Selection criteria for the Extending the Time for Thrombolysis in Emergency Neurological Deficits - Intra-Arterial (EXTEND-IA) trial included participants with an anterior large-vessel stroke who: were receiving a tissue plasminogen activator; were able to receive endovascular therapy within 6 hours of stroke onset; were functionally independent prior to the stroke; and had evidence of salvageable brain tissue and an ischemic core with a volume of less than 70 mL on computed tomography perfusion imaging.

Medically Necessary is defined as those services, treatments, procedures, equipment, drugs, devices, items or supplies furnished by a covered Provider that are required to identify or treat a Member's illness, injury or Mental Health Disorders, and which Company determines are covered under this Benefit Plan based on the criteria as follows in A through D:

A.  consistent with the symptoms or diagnosis and treatment of the Member's condition, illness, or injury; and

B.  appropriate with regard to standards of good medical practice; and

C.  not solely for the convenience of the Member, his or her Provider; and

D.  the most appropriate supply or level of care which can safely be provided to Member. When applied to the care of an Inpatient, it further means that services for the Member's medical symptoms or conditions require that the services cannot be safely provided to the Member as an Outpatient.

For the definition of medical necessity, “standards of good medical practice” means standards that are based on credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community, and physician specialty society recommendations, and the views of medical practitioners practicing in relevant clinical areas and any other relevant factors. BCBSMS makes no payment for services, treatments, procedures, equipment, drugs, devices, items or supplies which are not documented to be Medically Necessary. The fact that a Physician or other Provider has prescribed, ordered, recommended, or approved a service or supply does not in itself, make it Medically Necessary.

Investigative is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized as a generally accepted standard of good medical practice for the treatment of the condition being treated and; therefore, is not considered medically necessary. For the definition of Investigative, “generally accepted standards of medical practice” means standards that are based on credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community, and physician specialty society recommendations, and the views of medical practitioners practicing in relevant clinical areas and any other relevant factors. In order for equipment, devices, drugs or supplies [i.e, technologies], to be considered not investigative, the technology must have final approval from the appropriate governmental bodies, and scientific evidence must permit conclusions concerning the effect of the technology on health outcomes, and the technology must improve the net health outcome, and the technology must be as beneficial as any established alternative and the improvement must be attainable outside the testing/investigational setting.

POLICY HISTORY

4/25/2007: Policy Added.

7/19/2007: Reviewed and approved by the Medical Policy Advisory Committee (MPAC).

7/22/2008: Policy reviewed, no changes.

06/09/2010:  Policy description extensively re-written regarding use of CT perfusion imaging and FDA status of devices. Policy statement unchanged.  FEP verbiage added to the Policy Exceptions section.

07/29/2011: Policy reviewed; no changes.

01/09/2013: Policy reviewed; no changes.

11/15/2013: Policy reviewed; no changes to policy statement. Added "of the Brain" to the policy title for clarification purposes.

10/08/2014: Policy reviewed; description updated regarding acute stroke, subarachnoid hemorrhage and cerebral vasospasm, and brain tumors. Added "of the brain" to the policy statement for clarification purposes.

07/13/2015: Code Reference section updated for ICD-10.

06/09/2016: Policy number A.6.01.49 added. Investigative definition updated in Policy Guidelines section.

09/15/2017: Policy description updated. Added policy statement that computed tomography perfusion imaging may be considered medically necessary to select patients with anterior large-vessel stroke for mechanical embolectomy. Investigational statement revised to state that computed tomography perfusion imaging of the brain is considered investigational for all other indications. It previously stated: CT based perfusion imaging of the brain is considered investigational for all indications including the diagnosis and management of acute cerebral ischemia (stroke). Policy guidelines updated to add patient selection criteria. Code Reference section updated to change the code table from "Investigational" to "Medically Necessary." Added ICD-10 diagnosis codes I63.00 - I63.9.

12/04/2017: Policy description updated. Policy statements unchanged. Policy Guidelines updated to define medically necessary.

10/05/2018: Policy reviewed; no changes.

10/24/2019: Policy reviewed; no changes.

10/15/2020: Policy description updated. Policy statements unchanged.

01/07/2022: Policy description updated. Policy statements unchanged. Policy Guidelines updated regarding trials and to change "Nervous/Mental Conditions" to "Mental Health Disorders" and "Medically Necessary" to "medical necessity."

12/02/2022: Policy description updated regarding data for individuals experiencing stroke in the U.S. Policy statement updated to change "patients" to "individuals." Policy Guidelines updated.

10/16/2023: Policy reviewed; no changes.

02/14/2025: Policy reviewed; no changes.

01/01/2026: Code Reference section updated to add new CPT codes 70472 and 70473.

SOURCE(S)

Blue Cross Blue Shield Association Policy # 6.01.49

CODE REFERENCE

This may not be a comprehensive list of procedure codes applicable to this policy.

The code(s) listed below are ONLY medically necessary if the procedure is performed according to the "Policy" section of this document.

Medically Necessary Codes

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