Describe general diagnostic principles.
Evaluate for and manage acute neurological symptoms.
Ischemic stroke (anterior circulation stroke): See “Acute management checklist for ischemic stroke.”
TIA: See “Acute management checklist for TIA.”
Perform carotid artery imaging in all patients with symptomatic carotid stenosis.
Clinically significant carotid stenosis: narrowing of the carotid artery ≥ 50%
Moderate carotid stenosis: narrowing of the carotid artery by 50%–69%
Severe carotid stenosis: narrowing of the carotid artery 70%–99%
Screening for asymptomatic carotid stenosis is controversial and is detailed in the “Prevention” section below.
Noncontrast CT head or MRI brain is indicated for all patients with ischemic stroke or TIA.
Carotid artery stenosis typically occurs within 2 cm of the common carotid artery bifurcation
Describe the Carotid duplex US.
CDUS permits direct visualization of the vessel wall and flow measurement at the site of the stenosis by color Doppler ultrasound.
Indications: first-line imaging modality for suspected symptomatic carotid stenosis 
Focally increased velocity of blood flow (high-grade stenosis) or absence of blood flow (total occlusion) 
Increased peak systolic velocity
Increased thickness of the intima-media
Describe the MRA/CTA.
Confirmatory test if CDUS findings are suggestive of carotid stenosis
Simultaneous evaluation of head and neck vessels in patients with ischemic stroke 
Luminal narrowing at the site of the stenosis
Carotid plaques and calcification
The advantages of MRA include the lack of ionizing radiation and iodinated IV contrast.
MRA has a tendency to overestimate the degree of stenosis. 
CTA is suitable for patients with contraindications for MRI (e.g., implanted devices, claustrophobia). 
Describe the DSA.
DSA is commonly considered the gold standard for evaluating CAS. 
Consider if CDUS is inconclusive in patients who cannot undergo CTA or MRA.
Preprocedural planning (i.e., before carotid endarterectomy or carotid artery stenting)
Findings: Similar to CTA or MRA
Important consideration: DSA is an invasive procedure with a higher risk of mortality and stroke than imaging modalities with comparable diagnostic accuracy (e.g., CTA).