KEY FACTS
Terminology
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Carotid artery dissection (CAD): Tear in carotid artery wall allows blood to enter and delaminate wall layers
Imaging
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Extracranial internal CAD (ICAD) > > intracranial ICAD or CCAD
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20% of ICADs bilateral or involve vertebral arteries
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Pathognomonic findings of dissection: Intimal flap or double lumen
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Turbulent flow caused by fluttering intimal flap
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Smooth tapering stenosis typical sonographic appearance of ICAD; often occurs in young patients with no visible atherosclerotic plaque
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High ICAD beyond reach of ultrasound may only manifest as ↑ flow resistance in Doppler waveform and ↓ flow velocity due to distal obstruction
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Flap may be obscured by color blooming artifact on color Doppler and better seen on grayscale
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False lumen commonly demonstrates low peak flow velocity and reversed diastolic flow direction
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“Slosh” phenomenon of systolic forward-and-backward flow proximal to dissection highly typical
Top Differential Diagnoses
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Fibromuscular dysplasia
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Traumatic internal carotid artery pseudoaneurysm
Clinical Issues
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Ipsilateral pain in face, jaw, head, or neck
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Oculosympathetic palsy (miosis and ptosis, partial Horner syndrome), bruit (40%), pulsatile tinnitus
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Ischemic symptoms (cerebral or retinal TIA or stroke)
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Lower cranial nerve palsies (especially CNX)
Scanning Tips
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Beware of mirror image artifact in which IJ vein anterior to carotid is mirrored over carotid artery and can mimic dissection; rescan in different position
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B-flow technique may confirm flap more clearly due to lack of color blooming artifact
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In suspected dissection, reimage with higher frequency linear transducer (10-15 MHz) to help delineate flap
.
. Doppler waveforms of these 2 lumina both show high-resistance flow with rapid systolic upstroke and minimal forward flow during diastole.
and thrombosed false lumen 
. The larger thrombosed false lumen causes narrowing of the true lumen 
.
