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title: "Carotid Stenosis, Extracranial"
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docid: "1ebd8530-ebfc-4b36-9cd9-d9723c06f976"
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authors:
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- key: "07a2c087-6202-49e7-870b-7aa162d18f06"
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value: "Bronwyn E. Hamilton, MD"
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breadcrumbs:
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-
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name: "Vasculature"
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slug: "vasculature"
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treeNodeId: "9d3db335-364f-44ec-b2e2-30b03ce93228"
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-
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name: "Diagnosis"
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slug: "diagnosis"
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treeNodeId: "4a210126-9f87-404e-b419-a73f44d0e94c"
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-
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name: "Extracranial Cerebral Arteries"
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slug: "extracranial-cerebral-arteries"
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treeNodeId: "593e17de-cd84-4587-8349-872ed33d28c4"
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-
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name: "Carotid Stenosis, Extracranial"
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slug: "carotid-stenosis-extracranial"
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treeNodeId: null
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category: "Vasculature"
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cmeTopicId: "a5bae72a-b8c6-4e22-bcbb-7ac49e488023"
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documentVersionId: "e75ba73b-3257-4af2-b6dd-6aac9c6eae33"
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imageCount: 18
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lastUpdated: "07/09/21"
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pageDescription: "Carotid Stenosis, Extracranial"
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pageKeywords: "Vasculature, Diagnosis, Extracranial Cerebral Arteries, Carotid Stenosis, Extracranial"
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pageTitle: "Carotid Stenosis, Extracranial | STATdx"
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enhancedTitle: "Carotid Stenosis, Extracranial"
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type: "DX"
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references: true
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breadcrumbs:
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- "Vasculature"
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- "Diagnosis"
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- "Extracranial Cerebral Arteries"
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- "Carotid Stenosis, Extracranial"
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---
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# KEY FACTS
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- ## Terminology
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- Narrowing of cervical internal carotid artery or common carotid artery
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- ## Imaging
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- Extracranial carotid atherosclerotic vascular disease is most common at carotid bulb
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- Carotid duplex US shows vessel narrowing with turbulent flow, increased peak systolic velocity, and spectral broadening
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- CTA allows estimation of stenosis severity
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- MRA flow gap can occur in stenoses > 95%, causing misdiagnosis of occlusion
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- DSA is gold standard for evaluating severity of stenosis
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- "String" sign = very high grade stenosis
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- Slow antegrade "trickle" blood flow
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- ## Top Differential Diagnoses
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- Dissection
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- Fibromuscular dysplasia
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- Extrinsic compressive lesion (rare)
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- ## Pathology
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- Risk of stroke increases with stenosis severity, an indirect measure of plaque volume and potential for complicated plaque or embolization
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- ## Clinical Issues
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- NASCET showed that symptomatic patients with stenosis ≥ 70% (associated with stroke risk) benefit from carotid endarterectomy (CEA)
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- ACAS showed that asymptomatic patients with 60% stenosis benefit from CEA
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- SAPPHIRE compared CEA to carotid artery stenting (CAS) in high-risk patients with carotid stenosis
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- Lower complication rate with CAS
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- No difference in stroke after 3 years
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# TERMINOLOGY
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- ## Synonyms
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- Carotid atherosclerotic vascular disease (ASVD)
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- ## Definitions
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- Narrowing of cervical segment of internal carotid artery (ICA) or common carotid artery (CCA)
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- Carotid duplex US shows vessel narrowing with turbulent flow, increased peak systolic velocity, and spectral broadening
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- ### Location
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- Extracranial carotid ASVD is most common at carotid bulb
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- ### Size
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- Variable severity and length of stenosis; usually < 3 cm
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- Smooth or irregular narrowing ± ulceration ± intraluminal thrombus
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- ## CT Findings
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- ### NECT
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- Calcified ASVD plaque at CCA bifurcation ± ICA
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- May show thromboembolic or hemodynamic cerebral infarction
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- Typically ipsilateral anterior circulation
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- Posterior cerebral artery (PCA) stroke possible via posterior communicating artery or fetal PCA
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- ### CTA
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- Useful as screening tool
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- CTA allows estimation of stenosis severity
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- Multiplanar reformatted images in sagittal and coronal planes are helpful
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- Accuracy is reduced if extensive lesional calcification is present
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- Maximal carotid wall thickness ≥ 4 mm is predictive of future carotid ischemic stroke
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- Dental amalgam artifacts may hinder visualization
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- May show intraluminal thrombus as filling defect within enhanced vessel
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- Unreliable visualization of plaque ulceration
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- Patchy/homogeneous low density in wall may be seen with large necrotic/lipid plaque
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- ## MR Findings
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- ### T1WI
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- Reduced caliber of ICA flow void ± intraluminal signal due to thrombus or slow flow
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- Fat-saturated sequence if dissection is suspected as alternate etiology
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- Intramural crescentic high signal represents methemoglobin in vessel wall (dissection)
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- ### DWI
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- Most sensitive and specific for acute/subacute ischemia or infarction
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- ### MRA
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- Provides multidirectional imaging (vs. conventional DSA)
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- Time-of-flight (TOF) MRA: Intravoxel dephasing causes signal loss with flow turbulence due to stenosis
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- Affects 2D > 3D TOF images
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- Accentuates severity of stenosis
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- Gadolinium-enhanced MRA is superior to TOF sequences
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- Flow gap can occur in stenoses > 95%, causing misdiagnosis of occlusion
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- Brain T2WI, FLAIR, and DWI may show rosary-like lesions in centrum semiovale ipsilateral to stenosis, indicative of watershed ischemia or infarction
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- ## Ultrasonographic Findings
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- ### Grayscale ultrasound
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- Calcified plaque causes acoustic shadowing and may limit assessment of vessel lumen
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- ### Pulsed Doppler
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- Duplex US: Flow velocity within stenosis is proportional to severity of stenosis
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- Flow turbulence within and beyond stenosis
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- Spectral broadening: Increased range of velocities is seen in moderate to severe stenoses
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- ## Angiographic Findings
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- Conventional
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- DSA is gold standard for evaluation of carotid stenosis severity
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- Use of reverse-curve catheters (e.g., Simmons) can avoid inadvertent crossing of carotid bifurcation stenosis with guidewire and dislodgement of plaque
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- Intraluminal thrombus is seen as filling defect in contrast column
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- Can evaluate collateral flow to ischemic hemisphere from communicating arteries and leptomeningeal collaterals by studying contralateral ICA and dominant vertebral artery
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- "String" sign = very high grade stenosis, slow antegrade "trickle" blood flow
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- Typically seen during late phase of angiogram
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- May require prolonged DSA acquisitions for visualization
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- Preocclusive state with high risk of stroke
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- Important as carotid endarterectomy (CEA) or carotid artery stenting (CAS) may be an option if ICA is still patent
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- More sensitive and specific than CTA and MRA for subtotal occlusion with string sign
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- ## Other Modality Findings
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- CT/MR perfusion
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- Can provide assessment of collateral flow to territory normally perfused by stenotic carotid artery
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- Collateral circulation correlates with risk of hemodynamic ischemia or infarction
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- Measurement of carotid stenosis severity
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- North American Symptomatic Carotid Endarterectomy Trial (NASCET) method is most widely accepted
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- NASCET: Denominator is normal poststenotic ICA diameter
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- European Carotid Surgery Trial (ECST): Denominator is estimated normal diameter of carotid bulb
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- ## Imaging Recommendations
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- Ultrasound or CTA as screening tool
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- CTA/MRA for comprehensive cerebrovascular evaluation
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- DSA if US/CTA/MRA is equivocal or shows "occlusion"
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# DIFFERENTIAL DIAGNOSIS
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- ## Dissection
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- Typically spares carotid bulb and ICA origin
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- Usually no calcification (dystrophic Ca++ is rare)
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- Intimal flap with differential filling of true and false lumens on DSA
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- Crescentic intramural high signal (methemoglobin) on T1WI MR
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- ## Fibromuscular Dysplasia
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- Affects medium to large arteries
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- M:F = 1:3
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- Age peak: 25-50 years
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- Classically shows alternating segments of beading and stenoses involving extracranial ICA and external carotid, vertebral, and renal arteries
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- ## Extrinsic Compressive Lesion (Rare)
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- Carotid space neoplasm (e.g., carotid body paraganglioma, glomus jugulare tumor)
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- Risk of stroke increases with stenosis severity, an indirect measure of plaque volume and potential for complicated plaque/embolization
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- Larger plaques are complicated by hemorrhage, necrosis, and disruption of fibrous cap and intima, causing embolization
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- Plaque composition and surface morphology are also stroke risk factors
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- Irregular plaque surface: ↑ stroke risk on medical treatment for all degrees of stenosis
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- Hypoperfusion may cause watershed infarcts &/or centrum semiovale lesions
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- Significant ICA narrowing is identified in 20-30% of carotid territory stroke patients (vs. 5-10% of general population)
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- ## Gross Pathologic & Surgical Features
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- Fatty streak: Raised lesion due to fatty deposit in intima
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- Fibrous (fibrolipid) plaque: Cholesterol + fibrous tissue with collagen cap
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- Complicated plaque: Unstable; may rupture, thrombose, calcify, or hemorrhage
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- ## Microscopic Features
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- ASVD: Fatty streaks, lipid-laden macrophages and smooth muscle cells, fibrous cap, cholesterol deposits, foam cells, plaque rupture ± thrombus
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# CLINICAL ISSUES
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- ## Presentation
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- Stroke is 3rd most common cause of death in Western countries
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- Transient ischemic attack (TIA): Neurological deficit that spontaneously resolves in < 24 hours
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- 80% resolve in < 1 hour
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- Precedes 30% of strokes
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- 50% of subsequent strokes occur < 1 year from TIA
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- Reversible ischemic neurological deficit: Neurological deficit > 24 hours but < 3 weeks
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- Amaurosis fugax (transient, monocular embolic blindness)
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- Asymptomatic carotid bruit: 20% have > 60% ICA stenosis (3x normal population)
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- ## Natural History & Prognosis
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- Progressive
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- ## Treatment
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- Reduction of risk factors, which include hypertension, smoking, diabetic control, and hypercholesterolemia
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- Medical: Aspirin, statins
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- NASCET (1991)
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- Symptomatic stenosis ≥ 70% (associated with significant stroke risk) benefits from CEA
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- Symptomatic moderate stenosis (50-69%) also benefits from endarterectomy in selected cases
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- Asymptomatic Carotid Atherosclerosis Study (ACAS, 1995)
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- Asymptomatic patients with 60% stenosis benefit from CEA
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- CAS is becoming increasingly utilized and substantiated as viable alternative to CEA
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- CAS with distal protection device is associated with risk of periprocedural stroke ≤ CEA
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- Stenting and Angioplasty With Protection in Patients at High Risk for Endarterectomy (SAPPHIRE) 2004 study
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- Compared CEA with CAS in high-risk patients (comorbidities, age > 80 years, recent surgery, etc.) with symptomatic and asymptomatic carotid stenoses
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- Lower complication rate with CAS; no difference in stroke incidence after 3 years (7.1% CAS vs. 6.7% CEA)
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# DIAGNOSTIC CHECKLIST
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- ## Consider
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- Use of reverse-curve catheters for catheterization of CCA when carotid stenosis is suspected
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- ## Image Interpretation Pearls
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- MRA often exaggerates degree of stenosis
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- Look for intraluminal filling defect (CAS is contraindicated if intraluminal thrombus is present)
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- ## MIPS Considerations
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- MIPS Measure 195: Radiology: Stenosis Measurement in Carotid Imaging Reports
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- Last updated 2021
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- Percentage of final reports for carotid imaging studies (neck MRA, neck CTA, neck duplex ultrasound, carotid angiogram) performed that include **direct or indirect reference to** **measurements of distal internal carotid diameter as denominator for stenosis measurement**
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60075056-b951-47fe-b646-4817b546b29d
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## References
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# Selected References
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1. [MIPS Measure 195: Radiology: Stenosis Measurement in Carotid Imaging Reports (to reference if using CQMS). Centers for Medicare and Medicaid Services (CMS). 2021.](https://qpp.cms.gov/docs/QPP_quality_measure_specifications/CQM-Measures/2021_measure_195_MIPSCQM.pdf)
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1. [MIPS Measure 195: Radiology: Stenosis Measurement in Carotid Imaging Reports (to reference if using Medicare Part B claims). Centers for Medicare and Medicaid Services (CMS). 2021.](https://qpp.cms.gov/docs/QPP_quality_measure_specifications/Claims-Registry-Measures/2021_measure_195_MedicarePartBClaims.pdf)
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1. [Magge R et al: Clinical risk factors and CT imaging features of carotid atherosclerotic plaques as predictors of new incident carotid ischemic stroke: a retrospective cohort study. AJNR Am J Neuroradiol. 34(2):402-9, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=22859283%5Bpmid%5D)
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1. [Brott TG et al: 2011 ASA/ACCF/AHA/AANN/AANS/ACR/ASNR/CNS/SAIP/SCAI/SIR/SNIS/SVM/SVS guideline on the management of patients with extracranial carotid and vertebral artery disease: executive summary: Stroke. 42(8):e420-63, 2011. Erratum in: Stroke. 42(8):e541, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=-1%5Bpmid%5D)
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1. [Halliday A et al: Prevention of disabling and fatal strokes by successful carotid endarterectomy in patients without recent neurological symptoms: randomised controlled trial. Lancet. 363(9420):1491-502, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=15135594%5Bpmid%5D)
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1. [Yadav JS: Carotid stenting in high-risk patients: design and rationale of the SAPPHIRE trial. Cleve Clin J Med. 71 Suppl 1:S45-6, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=14964484%5Bpmid%5D)
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1. [No authors listed: Carotid endarterectomy for patients with asymptomatic internal carotid artery stenosis. National Institute of Neurological Disorders and Stroke. J Neurol Sci. 129(1):76-7, 1995](http://www.ncbi.nlm.nih.gov/pubmed/?term=7751850%5Bpmid%5D)
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## Images
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### Selected Images
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*Sagittal reformat CTA shows irregularity and focal high-grade stenosis of the proximal internal carotid artery (ICA) <img src='img/arrows/WS.png'/>, typical of atherosclerotic disease. Note areas of calcified plaque <img src='img/arrows/WO.png'/>, which indicate an atherosclerotic etiology.*
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*Sagittal reformat CTA shows irregularity and focal high-grade stenosis of the proximal internal carotid artery (ICA) <img src='img/arrows/WS.png'/>, typical of atherosclerotic disease. Note areas of calcified plaque <img src='img/arrows/WO.png'/>, which indicate an atherosclerotic etiology.*
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*Lateral DSA confirms similar findings to the CTA (same patient) typical of atherosclerotic high-grade carotid stenosis: Irregular short-segment narrowing <img src='img/arrows/WS.png'/> with more proximal ulceration <img src='img/arrows/WO.png'/>.*
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*Sagittal MRA shows a flow gap in the ICA <img src='img/arrows/WS.png'/>. MRA overestimates stenosis and occlusions; therefore, this must be confirmed with another vascular imaging modality to avoid misinterpretation.*
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*Color Doppler ultrasound (same patient) shows high flow velocities, anatomical narrowing, and spectral broadening, confirming that not an occlusion but a high-grade and hemodynamically significant stenosis (~ 80-99%) of the ICA bifurcation is present.*
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*Sagittal reformat CTA demonstrates a high-grade stenosis of the internal carotid artery distal to its origin <img src='img/arrows/WS.png'/> and irregular narrowing and ulceration more proximally at the carotid bifurcation <img src='img/arrows/WO.png'/>, findings typical for atherosclerotic narrowing.*
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*Lateral DSA (same patient) demonstrates similar findings compared with CTA: Ulceration and narrowing at the internal carotid artery origin <img src='img/arrows/WO.png'/> and more distal high-grade stenosis <img src='img/arrows/WS.png'/>.*
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*Sagittal CTA shows irregular ulcerated plaque <img src='img/arrows/WS.png'/> at the internal carotid artery origin, typical of atherosclerotic disease. Although a hemodynamically significant stenosis may not be present, this plaque is morphology prone to embolic complications.*
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*Oblique 3D reformation of a CTA shows diffuse beading of the distal cervical internal carotid artery <img src='img/arrows/WS.png'/>, typical in appearance for fibromuscular dysplasia. Both internal carotid and renal arteries (not shown) were similarly affected.*
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*Coronal MRA appears nearly normal in this patient with distal cervical left ICA dissection. Note the mild smoothly marginated caliber change <img src='img/arrows/WS.png'/> that is easily missed until compared with the contralateral side. The ICAs, unlike the vertebral arteries, normally demonstrate a symmetric size in the neck.*
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*Axial T1WI FS MR can be useful to confirm suspected dissection, as in this case (same patient) where crescentic mural hematoma is visible <img src='img/arrows/WS.png'/> around the luminal flow void.*
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### Additional Images
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*Oblique CCA DSA shows a calcified plaque at the carotid bifurcation extending into the ICA with associated stenosis <img src='img/arrows/WS.png'/>. An intraluminal filling defect <img src='img/arrows/WO.png'/> is seen. It represented a thrombus for which the patient was anticoagulated. DSA 5 days later revealed resolution of the thrombus, and carotid artery stenting was undertaken at that time.*
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*Carotid duplex spectral waveform in the same patient shows spectral broadening and a peak systolic velocity of 598 cm/s in keeping with a 70-99% stenosis.*
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*Oblique CCA DSA shows an ulcerated ASVD plaque at the carotid bifurcation <img src='img/arrows/WS.png'/>. There is an additional plaque distally <img src='img/arrows/BS.png'/> but no significant carotid stenosis.*
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*Carotid duplex ultrasound of the proximal ICA shows a moderate stenosis due to ASVD <img src='img/arrows/WS.png'/>. Within the stenotic segment there is flow turbulence as depicted by variations in color and intensity <img src='img/arrows/WO.png'/>.*
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*Sagittal gadolinium-enhanced MRA of the carotid bifurcation shows a flow gap at the ICA origin <img src='img/arrows/WS.png'/>. MRA typically overestimates the degree of stenosis.*
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*Sagittal CTA in a different patient shows a pinhole stenosis at the ICA origin <img src='img/arrows/WS.png'/>. Note adjacent calcifications within the ASVD plaque <img src='img/arrows/WC.png'/> and artifact from dental amalgam <img src='img/arrows/WO.png'/>.*
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*Lateral CCA DSA shows a high-grade stenosis of the ICA <img src='img/arrows/WS.png'/> and indentation of the vessel lumen by plaque <img src='img/arrows/WO.png'/>. Note gracile cervical ICA <img src='img/arrows/BS.png'/> due to proximal flow restriction.*
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*Oblique CCA DSA shows a high-grade ASVD stenosis at the carotid bulb <img src='img/arrows/WS.png'/> with associated calcifications <img src='img/arrows/BS.png'/>.*
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