GENERAL INFORMATION
IIt is an expectation that all patients receive care/services from a licensed clinician.  All appropriate supporting documentation, including recent pertinent office visit notes, laboratory data, and results of any special testing must be provided.  If applicable: All prior relevant imaging results and the reason that alternative imaging cannot be performed must be included in the documentation submitted. 

Where a specific clinical indication is not directly addressed in this guideline, medical necessity determination will be made based on widely accepted standard of care criteria. These criteria are supported by evidence-based or peer-reviewed sources such as medical literature, societal guidelines and state/national recommendations..

OVERVIEW:
CTP is not widely used especially in outpatients. It is useful in specific scenarios after initial CT and/or MR imaging has been obtained for assessment of, patients with acute stroke, and also a wide range of patients with other cerebrovascular diseases. In evaluating acute stroke it may assist in differentiating the unsalvageable core infarct and salvageable ischemic regions of the brain that may benefit from thrombectomy or thrombolysis. (2)

Acute Cerebral Ischemia (Stroke) — Cerebral perfusion CT can quantitatively distinguish the extent of irreversibly infarcted brain tissue (infarct core) from the severely ischemic but salvageable tissue (penumbra), providing a basis for the selection of acute stroke patients that are most likely to benefit from thrombolytic treatment.¹³

Cerebral Ischemia and Infarction and Evaluation of Vasospasm after Subarachnoid Hemorrhage (SAH)^14,15 — Cerebral perfusion CT measures cerebral blood flow, cerebral blood volume, and mean transit time which can be useful in identifying patients at risk for cerebral ischemia or infarction and for evaluation of vasospasm after subarachnoid hemorrhage. This information may be useful in identifying urgent medical or endovascular treatment. Catheter angiography is the gold standard for detecting vasospasm. Screening for vasospasm can be performed with TCD US (transcranial doppler ultrasound) and has high sensitivity and negative predictive value. CTA, CT perfusion or MRA may be useful in the setting of indeterminate TCD. CT or MR perfusion can help differentiate patients with vascular narrowing but normal perfusion due to the presence of collateral circulation from those without adequate collaterals.¹⁵

Carotid Artery Stent Placement/Revascularization — Cerebral perfusion CT provides a quantitative evaluation of cerebral perfusion and helps in the assessment of the hemodynamic modifications in patients with severe carotid stenosis. Pre-operatively, CTP may help identify patients at high risk of developing hyperperfusion syndrome after carotid revascularization. The syndrome may result in fatal outcomes. Presenting symptoms include “… throbbing frontotemporal or periorbital headache, confusion, macular oedema [sic], visual disturbances, seizures, or focal neurological deficits”.² “The presence of internal carotid artery (ICA) stenosis
≥ 90% is a main risk factor for the development of HPS. Other important risk factors include severe contralateral ICA disease, poor collateral flow, hypertension, and recent stroke or ischaemia [sic]”.² Post-operatively CTP provides valuable information for a more thorough assessment in the follow-up of patients after they have undergone carotid revascularization, especially when there is concern for hyperperfusion syndrome.¹³

Temporary Balloon Occlusion (TBO) — Balloon occlusion testing is utilized prior to a planned endovascular or surgical procedure that will disrupt blood supply to a part of the brain. Quantitative analysis of cerebral blood flow may be useful in identifying patient who may not tolerate permanent or prolonged occlusion. Due to the significant failure to predict strokes after sacrifice of the carotid artery, there is a vast number of monitoring techniques and protocols during preoperative test occlusion. As CTP monitoring of BTO entails carotid occlusion times ranging from 15 – 30 minutes and the need to transfer the patient with a catheter in place to the angiography suite, other methods with 60 – 90 second occlusion times are generally preferred.^3,4

Cerebrovascular Reserve — Cerebral perfusion CT, in conjunction with acetazolamide challenge in patients with intracranial vascular stenosis, can evaluate cerebrovascular reserve capacity and help in estimating the potential risk of stroke. It may help to identify candidates for bypass surgery and endovascular treatment to increase cerebral blood flow.

Intracranial tumors — Cerebral perfusion CT generates permeability measurements in images of brain tumors depicting areas of different blood flow within tumors and the surrounding tissues. This may allow for diagnosis and grading of tumors and may help to monitor treatment.

Policy
INDICATIONS FOR CEREBRAL PERFUSION CT¹
In the following settings after initial CT and/or MRI has been performed or when MRI is contraindicated:

• In the non-acute setting:
  • Pre-operative evaluation of cerebral blood flow in patients at high risk for developing cerebral hyperperfusion after carotid revascularization²
  • For assessment of cerebrovascular reserve by using acetazolamide challenge in individuals with intracranial vascular stenosis who are potential candidates for bypass surgery or neuroendovascular treatment^{3, 4}
  • For the assessment of microvascular permeability in individuals with intracranial neoplasms⁵
  • A follow-up study may be needed to help evaluate an individual’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
• In the acute setting:¹
  • For early detection of acute cerebral ischemia and infarct to determine the appropriateness of an intervention or procedure^6-10
  • Prediction of hemorrhagic transformation in acute ischemic stroke
  • Differentiating post-ictal paralysis or other stroke mimics from acute stroke after MRI has been completed or is contraindicated and will guide treatment6
  • For noninvasive evaluation of suspected vasospasm related cerebral ischemia/infarction and/or delayed cerebral ischemia after subarachnoid hemorrhage when transcranial Doppler cannot be done or is indeterminate¹¹
  • For the assessment of cerebral blood flow after carotid revascularization in individuals with severe carotid artery stenosis or signs/symptoms of cerebral hyperperfusion^2,11

Rationale
Contraindications and Preferred Studies
Contraindications and reasons why a CT/CTA cannot be performed may include: impaired renal function, significant allergy to IV contrast, pregnancy (depending on trimester).

Contraindications and reasons why an MRI/MRA cannot be performed may include: impaired renal function, claustrophobia, non-MRI compatible devices (such as non-compatible defibrillator or pacemaker), metallic fragments in a high-risk location, patient exceeds weight limit/dimensions of MRI machine.

Acute Cerebral Ischemia
Cerebral perfusion CT can quantitatively distinguish the extent of irreversibly infarcted brain tissue (infarct core) from the severely ischemic but salvageable tissue (penumbra), providing a basis for the selection of acute stroke patients that are most likely to benefit from thrombolytic treatment(2)

Cerebral Ischemia and Infarction and Evaluation of 
Vasospasm after Subarachnoid Hemorrhage (SAH)
Cerebral perfusion CT can be useful in identifying patients at risk for cerebral ischemia or infarction and for evaluation of vasospasm after subarachnoid hemorrhage. Catheter angiography is the gold standard for detecting vasospasm. Screening for vasospasm can be performed with TCD US (transcranial doppler ultrasound) and has high sensitivity and negative predictive value. CTA, CT perfusion or MRA may be useful in the setting of indeterminate TCD. CT or MR perfusion can help differentiate patients with vascular narrowing but normal perfusion due to the presence of collateral circulation from those without adequate collaterals.

Carotid Artery Stent Placement/Revascularization
Cerebral perfusion CT helps in the assessment of the hemodynamic modifications in patients with severe carotid stenosis. Pre-operatively, CTP may help identify patients at high risk of developing hyperperfusion syndrome after carotid revascularization. The presence of internal carotid artery (ICA) stenosis ≥90% is a main risk factor for the development of HPS. Other important risk factors include severe contralateral ICA disease, poor collateral flow, hypertension, and recent stroke or ischemia Post-operatively CTP provides valuable information for a more thorough assessment in the follow-up of patients after they have undergone carotid revascularization, especially when there is concern for hyperperfusion syndrome.(1,2)

Temporary Balloon Occlusion (TBO)
Ballon occlusion testing is used prior to a planned endovascular or surgical procedure that will disrupt blood flow to a part of the brain. CTP can be used to detect patients who may not tolerate a prolonged occlusion during a surgery/procedure. Given the length of testing and the need for transport other methods are generally preferred. (11,12)

References

1. American College of Radiology. ACR Appropriateness Criteria® Cerebrovascular Diseases-Aneurysm, Vascular Malformation, and Subarachnoid Hemorrhage. 2021; 2023: 
2. American College of Radiology , American Society of Neuroradiology , Society for Pediatric Radiology. ACR-ASNR-SPR practice parameter for the performance of computed tomography (CT) perfusion in neuroradiologic imaging. 2022; 2023: 
3. Mo D, Luo G, Wang B, Ma N, Gao F et al. Staged carotid artery angioplasty and stenting for patients with high-grade carotid stenosis with high risk of developing hyperperfusion injury: a retrospective analysis of 44 cases. Stroke Vasc Neurol. 2016; 1: 147-153. 10.1136/svn-2016-000024. 
4. Yoshie T, Ueda T, Takada T, Nogoshi S, Fukano T. Prediction of cerebral hyperperfusion syndrome after carotid artery stenting by . Neuroradiology. 2016; 58: 253-9. 
5. Jain R. Perfusion CT imaging of brain tumors: an overview. AJNR Am J Neuroradiol. Oct 2011; 32: 1570-7. 10.3174/ajnr.A2263. 
6. Salmela M B, Mortazavi S, Jagadeesan B D, Broderick D F, Burns J et al. ACR appropriateness criteria® cerebrovascular disease. Journal of the American College of Radiology. 2017; 14: S34-S61. 
7. Simonsen C, Leslie-Mazwi T, Thomalla G. Which Imaging Approach Should Be Used for Stroke of Unknown Time of Onset? Stroke. Jan 2021; 52: 373-380.10.1161 /strokeaha.120.032020. 
8. Wintermark M, Sanelli P C, Albers G W, Bello J, Derdeyn C et al. Imaging recommendations for acute stroke and transient ischemic attack patients: A joint statement by the American Society of Neuroradiology, the American College of Radiology, and the Society of NeuroInterventional Surgery. AJNR Am J Neuroradiol. 2013; 34: E117-27. 10.3174/ajnr.A3690. 
9. Guerrero W, Dababneh H, Eisenschenk S. The role of perfusion CT in identifying stroke mimics in the emergency room: a case of status epilepticus presenting with perfusion CT alterations. International journal of emergency medicine. 2012; 5: 4-4. 10.1186/1865-1380-5-4. 
10. Vasquez R, Waters M, Skowlund C, Mocco J, Hoh B. Computed tomographic perfusion imaging of non-hemorrhagic cerebral hyperperfusion syndrome and reversal following medical treatment after carotid artery angioplasty and stenting. J Neurointerv Surg. May 2012; 4: e2. 10.1136/jnis.2010.003558. 
11. Galego O, Nunes C, Morais R, Sargento-Freitas J, Sales F. Monitoring balloon test occlusion of the internal carotid artery with transcranial Doppler. A case report and literature review. Neuroradiol J. Feb 2014; 27: 115-9. 10.15274/nrj-2014-10014. 
12. Sorteberg A. Balloon occlusion tests and therapeutic vessel occlusions revisited: when, when not, and how. AJNR Am J Neuroradiol. May 2014; 35: 862-5. 10.3174/ajnr.A3852. 
13. Vagal A, Leach J, Fernandez-Ulloa M, Zuccarello M. The Acetazolamide Challenge: Techniques and Applications in the Evaluation of Chronic Cerebral Ischemia. American Journal of Neuroradiology. 2009; 30: true. 10.3174/ajnr.A1538. 
14. You S, Jo S, Kim Y, Lee J, Jo K. Pre- and Post-Angioplasty Perfusion CT with Acetazolamide Challenge in Patients. Journal of Korean Neurosurgical Society. 2013; 54: 280-8.

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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