Description
Computed tomography angiography (CTA) is recognized as a valuable diagnostic tool for the management of patients with cerebrovascular disease. With its three-dimensional reconstructions, CTA can simultaneously demonstrate the bony skull base and its related vasculature. CTA use of ionizing radiation and an iodine-based intravascular contrast medium is a disadvantage when compared to magnetic resonance angiography (MRA) but it is quicker and requires less patient cooperation than MRA. CTA is much less invasive than catheter angiography which involves injecting contrast material into an artery.

CTA for Evaluation of Aneurysm – CTA is useful in the detection of cerebral aneurysms. The sensitivity of CTA to detect cerebral aneurysms < 5 mm is higher than that with digital subtraction angiography (DSA). Most aneurysms missed with CTA are < 3mm. Aneurysms in the region of the anterior clinoid process may extend into the subarachnoid space where they carry the threat of hemorrhage. CTA can help delineate the borders of the aneurysm in relation to the subarachnoid space and may help detect acute ruptured aneurysms. It may be used in the selection of patients for surgical or endovascular treatment of ruptured intracranial aneurysms.

CTA for Screening of Patients with first degree relative (parent, brother, sister or child) have a history of aneurysm – Data has suggested that individuals with a parent, brother, sister, or child harboring an intracranial aneurysm are at increased risk of aneurysms. It is likely that multiple genetic and environmental risk factors contribute to the increased risk.

CTA for evaluation of Arteriovenous Malformation (AVM) – A good correlation has been found between catheter angiography and CTA in the detection of arteriovenous malformations. CTA allows calculation of the volume of an AVM nidus and identifies and quantifies embolic material within it. CTA may be used for characterization and stereotactic localization before surgical resection or radiosurgical treatment of arteriovenous malformations.

CTA and non-aneurysmal vascular malformations – Non-aneurysmal vascular malformations can be divided in low flow vascular malformations and high flow vascular malformations. Low flow vascular malformations include dural venous anomalies (DVA), cavernomas and capillary telangiectasias. High flow vascular malformations include AVM and dural arteriovenous fistulas (dAVF). For low flow malformations, MRI is the study of choice. There is limited medical literature to support vascular imagining (CTA or MRA). CTA plays a limited role in the assessment of cavernoma but may be used to demonstrate a DVA. MRA is not usually helpful in the assessment of cavernoma, capillary telangiectasia, and DVA. Vascular imaging is indicated in high flow vascular malformations (ACR, 2017, 2019; Lee, 2012).

CTA and recent stroke or transient ischemic attack – A stroke or central nervous system infarction is defined as brain, spinal cord, or retinal cell death attributable to ischemia, based on neuropathological, neuroimaging, and/or clinical evidence of permanent injury. … Ischemic stroke specifically refers to central nervous system infarction accompanied by overt symptoms, whereas silent infarction causes no known symptoms (Sacco, 2013). If imaging or pathology is not available, a clinical stroke is diagnosed by symptoms persisting for more than 24 hours. Ischemic stroke can be further classified by the type and location of ischemia and the presumed etiology of the brain injury. These include large-artery atherosclerotic occlusion (extracranial or intracranial), cardiac embolism, small-vessel disease and less commonly dissection, hypercoagulable states, sickle cell disease and undetermined causes (Kernan, 2014). TIAs, in contrast, are a brief episode of neurological dysfunction caused by focal brain or retinal ischemia, with clinical symptoms typically lasting less than one hour, and without evidence of acute infarction on imaging (Easton, 2009). On average, the annual risk of future ischemic stroke after a TIA or initial ischemic stroke is 3–4%, with an incidence as high as 11% over the next 7 days and 24–29% over the following 5 years. This has significantly decreased in the last half century due to advances in secondary prevention (Hong, 2011).

When revascularization therapy is not indicated or available in patients with an ischemic stroke or TIA, the focus of the work-up is on secondary prevention. This includes noninvasive vascular imaging to identify the underlying etiology, assess immediate complications and risk of future stroke. The majority of stroke evaluations take place in the inpatient setting. Admitting TIA patients is reasonable if they present within 72 hours and have an ABCD (2) score ≥ 3, indicating high risk of early recurrence, or the evaluation cannot be rapidly completed on an outpatient basis (Easton, 2009). Minimally, both stroke and TIA should have an evaluation for high-risk modifiable factors such as carotid stenosis atrial fibrillation as the cause of ischemic symptoms (Kernan, 2014). Diagnostic recommendations include: neuroimaging evaluation as soon as possible, preferably with magnetic resonance imaging, including DWI; noninvasive imaging of the extracranial vessels should be performed, and noninvasive imaging of intracranial vessels is reasonable (Wintermark, 2013).

Patients with a history of stroke and recent work up with new signs or symptoms indicating progression or complications of the initial CVA should have repeat brain imaging as an initial study. Patients with remote or silent strokes discovered on imaging should be evaluated for high-risk modifiable risk factors based on the location and type of the presumed etiology of the brain injury.

CTA for Evaluation of Vertebrobasilar Insufficiency (VBI) – Multidetector CT angiography (MDCTA) may be used in the evaluation of vertebral artery pathologies. The correlation between MDCTA and color Doppler sonography is moderate. CTA is used for minimally invasive follow-up after intracranial stenting for VBI. It enables visualization of the patency of the stent lumen and provides additional information about all brain arteries and the brain parenchyma.

CTA and Intracerebral Hemorrhage – CTA is useful as a screening tool for an underlying vascular abnormality in the evaluation of spontaneous intracerebral hemorrhage (ICH). Etiologies of spontaneous ICH include tumor, vascular malformation, aneurysm, hypertensive arteriopathy, cerebral amyloid angiopathy, venous thrombosis, vasculitis, RCVS, drug induced vasospasm, venous sinus thrombosis, Moyomoya disease, anticoagulant use and hemorrhagic transformation of an ischemic infarct. History can help point to a specific etiology. Possible risk factors for the presence of underlying vascular abnormalities include age younger than 65, female, lobar or intraventricular location, and the absence of hypertension or impaired coagulation (Delgado, 2009). 

CTV and Central Venous Thrombosis – a CT Venogram is indicted for the evaluation of a central venous thrombosis/dural sinus thrombosis. The most frequent presentations are isolated headache, intracranial hypertension syndrome, seizures, focal neurological deficits and encephalopathy. Risk factors are hypercoagulable states inducing genetic prothrombotic conditions, antiphospholipid syndrome and other acquired prothrombotic diseases such as cancer, oral contraceptives, pregnancy, puerperium (6 weeks postpartum), infections, and trauma. Since venous thrombosis can cause SAH, infarctions and hemorrhage parenchymal imaging with MRI/CT is also appropriate. (Bushnell, 2014; Courinho, 2015; Ferro, 2016; Waleki, 2015).

MRA and dissection – Craniocervical dissections can be spontaneous or traumatic. Patients with blunt head or neck trauma who meet Denver Screening criteria should be assessed for cerebrovascular injury (although about 20% will not meet criteria). The criteria include: focal or lateralizing neurological deficits (not explained by head CT), infarct on head CT, face, basilar skull, or cervical spine fractures, cervical hematomas that are not expanding, glasgow coma score less than 8 without CT findings, massive epistaxis, cervical bruit or thrill (Franz, 2012; Liang, 2013; Mundinger, 2013; Simon, 2019). Spontaneous dissection presents with headache, neck pain with neurological signs or symptoms. There is often minor trauma or precipitating factor (i.e., exercise, neck manipulation). Dissection is thought to occur due to weakness of the vessel wall and there may be an underlying connective tissue disorder. Dissection of the extracranial vessels can extend intracranially and/or lead to thrombus which can migrate into the intracranial circulation causing ischemia. Therefore, MRA of the head and neck is warranted (Nash, 2019; Shakir, 2016). 

Policy 
BRAIN CTA is considered MEDICALLY NECESSARY for the following indications:

INDICATIONS FOR BRAIN CTA:
Brain CT/CTA are not approvable simultaneously unless they meet the criteria described below in the Indications for Brain CT/Brain CTA combination studies section. If there is a combination request* for an overlapping body part, either requested at the same time or sequentially (within the past 3 months) the results of the prior study should be:

• Inconclusive or show a need for additional or follow up imaging evaluation OR
• The office notes should clearly document an indication why overlapping imaging is needed and how it will change management for the patient.

(*Unless approvable in the combination section as noted in the guidelines)

Patients with claustrophobia, limited ability to cooperate, an implanted device or in an urgent scenario may be better suited for CTA; whereas those with renal disease or iodine contrast allergy should have MRA.¹

For evaluation of suspected intracranial vascular disease^{2, 3}

Aneurysm screening

• Screening for suspected intracranial aneurysm in patient with first-degree family history (parent, brother, sister, or child) of intracranial aneurysm                     

          Note: Repeat study is recommended every 5 years⁴

• Screening for aneurysm in polycystic kidney disease (after age 30), Loeys-Dietz syndrome‡, fibromuscular dysplasia, spontaneous coronary arteries dissection (SCAD), or known aortic coarctation (after age 10)^5-9

‡For Loeys-Dietz, imaging should be repeated at least every two years

Vascular abnormalities

• Suspected vascular malformation (arteriovenous malformation (AVM) or dural arteriovenous fistula) in patient with previous or indeterminate imaging study
• Thunderclap headache with continued concern for underlying vascular abnormality after initial negative brain imaging > 6 hours after onset^10-13          

         Note: Negative brain CT < 6 hours after headache onset excludes subarachnoid hemorrhage in neurologically intact patients¹³

• Headache associated with exercise or sexual activity¹⁴
• Isolated third nerve palsy (oculomotor) with pupil involvement to evaluate for aneurysm15
• Pulsatile tinnitus to identify a suspected arterial vascular etiology^16,17

Note: MRI is the study of choice for detecting low flow malformations (see background)^18-20

Cerebrovascular Disease
Ischemic

• Recent ischemic stroke or transient ischemic attack (See background section)^21,22
• Known or suspected vertebrobasilar insufficiency (VBI) in patients with symptoms such as dizziness, vertigo, headaches, diplopia, blindness, vomiting, ataxia, weakness in both sides of the body, or abnormal speech^{23, 24}

Hemorrhagic

• Known subarachnoid hemorrhage (SAH)²⁵
• Known cerebral intraparenchymal hemorrhage with concern for underlying vascular abnormality

Venous and MRV is contraindicated or cannot be performed²⁶- CTV**

• Suspected venous thrombosis (dural sinus thrombosis)^27,28
• Distinguishing benign intracranial hypertension (pseudotumor cerebri) from dural sinus thrombosis^29,30

Sickle cells disease (ischemic and/or hemorrhagic) and MRA is contraindicated or cannot be performed31

• Neurological signs or symptoms in sickle cell disease
• Stroke risk in sickle cell patients (2 - 16 years of age) with a transcranial doppler velocity > 200

Vasculitis with initial laboratory workup (such as ESR, CRP, serology)³²

• Suspected secondary CNS vasculitis based on neurological signs or symptoms in the setting of an underlying systemic disease with abnormal inflammatory markers or autoimmune antibodies
• Suspected primary CNS vasculitis based on neurological signs and symptoms with completed infectious/inflammatory lab work-up33, 34

Other intracranial vascular disease

• Suspected Moyomoya disease^35,36
• Suspected reversible cerebral vasoconstriction syndrome37
• Giant cell arteritis with suspected intracranial involvement38

For evaluation of known intracranial vascular disease^2,3

• Known intracranial aneurysm, treated aneurysm, or known vascular malformation (i.e., AVM or dural arteriovenous fistula)
• Vascular abnormality visualized on previous brain imaging that is equivocal or needs further evaluation
• Known vertebrobasilar insufficiency with new or worsening signs or symptoms (VBI^)23,24
• Known vasculitis, reversible cerebral vasoconstriction syndrome or Moyomoya disease^{33,35- 37}

Pre-operative/procedural evaluation for brain/skull surgery

• Pre-operative evaluation for a planned surgery or procedure

Post-operative/procedural evaluation^39,40

• A follow-up study may be needed to help evaluate a patient’s progress after treatment, procedure, intervention, or surgery. Documentation requires a medical reason that clearly indicates why additional imaging is needed for the type and area(s) requested.

Indications for Brain CTA/Neck CTA combination studies

• Recent ischemic stroke or transient ischemic attack²¹
• Known or suspected vertebrobasilar insufficiency (VBI) in patients with symptoms such as dizziness, vertigo, headaches, diplopia, blindness, vomiting, ataxia, weakness in both sides of the body, or abnormal speech^23,24
• Suspected carotid or vertebral artery dissection; secondary to trauma or spontaneous due to weakness of vessel wall^41,42
• Asymptomatic patients with an abnormal ultrasound of the neck or carotid duplex imaging (e.g., carotid stenosis ≥ 70%, technically limited study, aberrant direction of flow in the carotid or vertebral arteries) and patient is surgery or angioplasty candidate^43-45
• Symptomatic patients with an abnormal ultrasound of the neck or carotid duplex imaging (e.g., carotid stenosis ≥ 50%, technically limited study, aberrant direction of flow in the carotid or vertebral arteries) and patient is surgery or angioplasty candidate^43,46
• Pulsatile tinnitus to identify a suspected arterial vascular etiology^16,17

Indications for Brain CT/Brain CTA combination studies^2,3

• Recent ischemic stroke or transient ischemic attack (TIA) when MRI is contraindicated or cannot be performed
• Acute, sudden onset of headache with personal history of a vascular abnormality or first- degree family history of aneurysm
• Headache associated with exercise or sexual activity when MRI is contraindicated or cannot be performed¹⁴
• Suspected venous thrombosis (dural sinus thrombosis) and MRI is contraindicated or cannot be performed – CT/CTV**
• Neurological signs or symptoms in sickle cell patients when MRI is contraindicated or cannot be performed
• High stroke risk in sickle cell patients (2 - 16 years of age) with a transcranial doppler velocity > 200 when MRI is contraindicated or cannot be performed

Indications for Brain CT/Brain CTA/Neck CTA combination studies

• Recent ischemic stroke or transient ischemic attack (TIA)^2,3 when MRI is contraindicated or cannot be performed
• Approved indications as noted above and being performed in high-risk populations (in whom MRI is contraindicated or cannot be performed) and will need anesthesia for the procedure and there is a suspicion of concurrent intracranial pathology

References  

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Coding Section 

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each Policy. They may not be all-inclusive. 

This medical policy was developed through consideration of peer-reviewed medical literature generally recognized by the relevant medical community, U.S. FDA approval status, nationally accepted standards of medical practice and accepted standards of medical practice in this community, Blue Cross Blue Shield Association technology assessment program (TEC) and other non-affiliated technology evaluation centers, reference to federal regulations, other plan medical policies, and accredited national guidelines.

"Current Procedural Terminology © American Medical Association. All Rights Reserved" 

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