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KEY FACTS

Terminology
- Narrowing of cervical internal carotid artery or common carotid artery
Imaging
- Extracranial carotid atherosclerotic vascular disease is most common at carotid bulb
- Carotid duplex US shows vessel narrowing with turbulent flow, increased peak systolic velocity, and spectral broadening
- CTA allows estimation of stenosis severity
- MRA flow gap can occur in stenoses > 95%, causing misdiagnosis of occlusion
- DSA is gold standard for evaluating severity of stenosis - "String" sign = very high grade stenosis - Slow antegrade "trickle" blood flow
Top Differential Diagnoses
- Dissection
- Fibromuscular dysplasia
- Extrinsic compressive lesion (rare)
Pathology
- Risk of stroke increases with stenosis severity, an indirect measure of plaque volume and potential for complicated plaque or embolization
Clinical Issues
- NASCET showed that symptomatic patients with stenosis ≥ 70% (associated with stroke risk) benefit from carotid endarterectomy (CEA)
- ACAS showed that asymptomatic patients with 60% stenosis benefit from CEA
- SAPPHIRE compared CEA to carotid artery stenting (CAS) in high-risk patients with carotid stenosis - Lower complication rate with CAS - No difference in stroke after 3 years

TERMINOLOGY

Synonyms
- Carotid atherosclerotic vascular disease (ASVD)
Definitions
- Narrowing of cervical segment of internal carotid artery (ICA) or common carotid artery (CCA)

IMAGING

General Features

Best diagnostic clue

- Carotid duplex US shows vessel narrowing with turbulent flow, increased peak systolic velocity, and spectral broadening

Location

- Extracranial carotid ASVD is most common at carotid bulb

Size

- Variable severity and length of stenosis; usually < 3 cm

Smooth or irregular narrowing ± ulceration ± intraluminal thrombus

CT Findings

NECT

- Calcified ASVD plaque at CCA bifurcation ± ICA
- May show thromboembolic or hemodynamic cerebral infarction
        - Typically ipsilateral anterior circulation
        - Posterior cerebral artery (PCA) stroke possible via posterior communicating artery or fetal PCA

CTA

- Useful as screening tool
- CTA allows estimation of stenosis severity
        - Multiplanar reformatted images in sagittal and coronal planes are helpful
        - Accuracy is reduced if extensive lesional calcification is present
        - Maximal carotid wall thickness ≥ 4 mm is predictive of future carotid ischemic stroke
- Dental amalgam artifacts may hinder visualization
- May show intraluminal thrombus as filling defect within enhanced vessel
- Unreliable visualization of plaque ulceration
- Patchy/homogeneous low density in wall may be seen with large necrotic/lipid plaque

MR Findings

T1WI

- Reduced caliber of ICA flow void ± intraluminal signal due to thrombus or slow flow
- Fat-saturated sequence if dissection is suspected as alternate etiology
        - Intramural crescentic high signal represents methemoglobin in vessel wall (dissection)

DWI

- Most sensitive and specific for acute/subacute ischemia or infarction

MRA

- Provides multidirectional imaging (vs. conventional DSA)
- Time-of-flight (TOF) MRA: Intravoxel dephasing causes signal loss with flow turbulence due to stenosis
        - Affects 2D > 3D TOF images
        - Accentuates severity of stenosis
        - Gadolinium-enhanced MRA is superior to TOF sequences
- Flow gap can occur in stenoses > 95%, causing misdiagnosis of occlusion

Brain T2WI, FLAIR, and DWI may show rosary-like lesions in centrum semiovale ipsilateral to stenosis, indicative of watershed ischemia or infarction

Ultrasonographic Findings

Grayscale ultrasound

- Calcified plaque causes acoustic shadowing and may limit assessment of vessel lumen

Pulsed Doppler

- Duplex US: Flow velocity within stenosis is proportional to severity of stenosis
- Flow turbulence within and beyond stenosis
- Spectral broadening: Increased range of velocities is seen in moderate to severe stenoses

Angiographic Findings
- Conventional - DSA is gold standard for evaluation of carotid stenosis severity - Use of reverse-curve catheters (e.g., Simmons) can avoid inadvertent crossing of carotid bifurcation stenosis with guidewire and dislodgement of plaque - Intraluminal thrombus is seen as filling defect in contrast column - Can evaluate collateral flow to ischemic hemisphere from communicating arteries and leptomeningeal collaterals by studying contralateral ICA and dominant vertebral artery - "String" sign = very high grade stenosis, slow antegrade "trickle" blood flow - Typically seen during late phase of angiogram - May require prolonged DSA acquisitions for visualization - Preocclusive state with high risk of stroke - Important as carotid endarterectomy (CEA) or carotid artery stenting (CAS) may be an option if ICA is still patent - More sensitive and specific than CTA and MRA for subtotal occlusion with string sign
Other Modality Findings
- CT/MR perfusion - Can provide assessment of collateral flow to territory normally perfused by stenotic carotid artery - Collateral circulation correlates with risk of hemodynamic ischemia or infarction
- Measurement of carotid stenosis severity - North American Symptomatic Carotid Endarterectomy Trial (NASCET) method is most widely accepted - NASCET: Denominator is normal poststenotic ICA diameter - European Carotid Surgery Trial (ECST): Denominator is estimated normal diameter of carotid bulb
Imaging Recommendations
- Ultrasound or CTA as screening tool
- CTA/MRA for comprehensive cerebrovascular evaluation
- DSA if US/CTA/MRA is equivocal or shows "occlusion"

DIFFERENTIAL DIAGNOSIS

Dissection
- Typically spares carotid bulb and ICA origin
- Usually no calcification (dystrophic Ca++ is rare)
- Intimal flap with differential filling of true and false lumens on DSA
- Crescentic intramural high signal (methemoglobin) on T1WI MR
Fibromuscular Dysplasia
- Affects medium to large arteries
- M:F = 1:3
- Age peak: 25-50 years
- Classically shows alternating segments of beading and stenoses involving extracranial ICA and external carotid, vertebral, and renal arteries
Extrinsic Compressive Lesion (Rare)
- Carotid space neoplasm (e.g., carotid body paraganglioma, glomus jugulare tumor)

PATHOLOGY

General Features

Etiology

- Risk of stroke increases with stenosis severity, an indirect measure of plaque volume and potential for complicated plaque/embolization
        - Larger plaques are complicated by hemorrhage, necrosis, and disruption of fibrous cap and intima, causing embolization
- Plaque composition and surface morphology are also stroke risk factors
- Irregular plaque surface: ↑ stroke risk on medical treatment for all degrees of stenosis
- Hypoperfusion may cause watershed infarcts &/or centrum semiovale lesions

Significant ICA narrowing is identified in 20-30% of carotid territory stroke patients (vs. 5-10% of general population)

Gross Pathologic & Surgical Features
- Fatty streak: Raised lesion due to fatty deposit in intima
- Fibrous (fibrolipid) plaque: Cholesterol + fibrous tissue with collagen cap
- Complicated plaque: Unstable; may rupture, thrombose, calcify, or hemorrhage
Microscopic Features
- ASVD: Fatty streaks, lipid-laden macrophages and smooth muscle cells, fibrous cap, cholesterol deposits, foam cells, plaque rupture ± thrombus

CLINICAL ISSUES

Presentation
- Stroke is 3rd most common cause of death in Western countries
- Transient ischemic attack (TIA): Neurological deficit that spontaneously resolves in < 24 hours - 80% resolve in < 1 hour - Precedes 30% of strokes - 50% of subsequent strokes occur < 1 year from TIA
- Reversible ischemic neurological deficit: Neurological deficit > 24 hours but < 3 weeks
- Amaurosis fugax (transient, monocular embolic blindness)
- Asymptomatic carotid bruit: 20% have > 60% ICA stenosis (3x normal population)
Natural History & Prognosis
- Progressive
Treatment
- Reduction of risk factors, which include hypertension, smoking, diabetic control, and hypercholesterolemia
- Medical: Aspirin, statins
- NASCET (1991) - Symptomatic stenosis ≥ 70% (associated with significant stroke risk) benefits from CEA - Symptomatic moderate stenosis (50-69%) also benefits from endarterectomy in selected cases
- Asymptomatic Carotid Atherosclerosis Study (ACAS, 1995) - Asymptomatic patients with 60% stenosis benefit from CEA
- CAS is becoming increasingly utilized and substantiated as viable alternative to CEA
- CAS with distal protection device is associated with risk of periprocedural stroke ≤ CEA
- Stenting and Angioplasty With Protection in Patients at High Risk for Endarterectomy (SAPPHIRE) 2004 study - Compared CEA with CAS in high-risk patients (comorbidities, age > 80 years, recent surgery, etc.) with symptomatic and asymptomatic carotid stenoses - Lower complication rate with CAS; no difference in stroke incidence after 3 years (7.1% CAS vs. 6.7% CEA)

DIAGNOSTIC CHECKLIST

Consider
- Use of reverse-curve catheters for catheterization of CCA when carotid stenosis is suspected
Image Interpretation Pearls
- MRA often exaggerates degree of stenosis
- Look for intraluminal filling defect (CAS is contraindicated if intraluminal thrombus is present)
MIPS Considerations
- MIPS Measure 195: Radiology: Stenosis Measurement in Carotid Imaging Reports - Last updated 2021 - 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

60075056-b951-47fe-b646-4817b546b29d

References

Selected References

Images

Selected Images

Sagittal reformat CTA shows irregularity and focal high-grade stenosis of the proximal internal carotid artery (ICA) , typical of atherosclerotic disease. Note areas of calcified plaque , which indicate an atherosclerotic etiology.

Lateral DSA confirms similar findings to the CTA (same patient) typical of atherosclerotic high-grade carotid stenosis: Irregular short-segment narrowing with more proximal ulceration .

Sagittal MRA shows a flow gap in the ICA . MRA overestimates stenosis and occlusions; therefore, this must be confirmed with another vascular imaging modality to avoid misinterpretation.

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.

Sagittal reformat CTA demonstrates a high-grade stenosis of the internal carotid artery distal to its origin and irregular narrowing and ulceration more proximally at the carotid bifurcation , findings typical for atherosclerotic narrowing.

Lateral DSA (same patient) demonstrates similar findings compared with CTA: Ulceration and narrowing at the internal carotid artery origin and more distal high-grade stenosis .

Sagittal CTA shows irregular ulcerated plaque 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.

Oblique 3D reformation of a CTA shows diffuse beading of the distal cervical internal carotid artery , typical in appearance for fibromuscular dysplasia. Both internal carotid and renal arteries (not shown) were similarly affected.

Coronal MRA appears nearly normal in this patient with distal cervical left ICA dissection. Note the mild smoothly marginated caliber change that is easily missed until compared with the contralateral side. The ICAs, unlike the vertebral arteries, normally demonstrate a symmetric size in the neck.

Axial T1WI FS MR can be useful to confirm suspected dissection, as in this case (same patient) where crescentic mural hematoma is visible around the luminal flow void.

Additional Images

Oblique CCA DSA shows a calcified plaque at the carotid bifurcation extending into the ICA with associated stenosis . An intraluminal filling defect 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.

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.

Oblique CCA DSA shows an ulcerated ASVD plaque at the carotid bifurcation . There is an additional plaque distally but no significant carotid stenosis.

Carotid duplex ultrasound of the proximal ICA shows a moderate stenosis due to ASVD . Within the stenotic segment there is flow turbulence as depicted by variations in color and intensity .

Sagittal gadolinium-enhanced MRA of the carotid bifurcation shows a flow gap at the ICA origin . MRA typically overestimates the degree of stenosis.

Sagittal CTA in a different patient shows a pinhole stenosis at the ICA origin . Note adjacent calcifications within the ASVD plaque and artifact from dental amalgam .

Lateral CCA DSA shows a high-grade stenosis of the ICA and indentation of the vessel lumen by plaque . Note gracile cervical ICA due to proximal flow restriction.

Oblique CCA DSA shows a high-grade ASVD stenosis at the carotid bulb with associated calcifications .

25 KiB Raw Blame History

KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

TERMINOLOGY

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Size

CT Findings

NECT

CTA

MR Findings

T1WI

DWI

MRA

Ultrasonographic Findings

Grayscale ultrasound

Pulsed Doppler

Angiographic Findings

Other Modality Findings

Imaging Recommendations

DIFFERENTIAL DIAGNOSIS

Dissection

Fibromuscular Dysplasia

Extrinsic Compressive Lesion (Rare)

PATHOLOGY

General Features

Etiology

Gross Pathologic & Surgical Features

Microscopic Features

CLINICAL ISSUES

Presentation

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

MIPS Considerations

References

Selected References

Images

Selected Images

Additional Images

25 KiB

Raw Blame History