CLINICAL HISTORY
A 69-year-old man with sudden onset of left leg and arm weakness two days ago. Magnetic resonance imaging (MRI) showed a right middle cerebral artery territory stroke.
4
DIAGNOSIS
Carotid stenosis
Differential Diagnosis
Carotid artery dissection
CLINICAL PRESENTATION
Patients with symptomatic carotid artery stenosis present with anterior circulation ischemia, either in the form of transient ischemic attacks (TIAs) or persistent neurologic deficits. Atherosclerotic plaque in the internal carotid embolizes and occludes branches in the distal anterior circulation, with resultant neurologic sequelae. Amaurosis fugax, transient unilateral loss of vision, is a classic type of TIA associated with carotid stenosis. Posterior circulation strokes and TIAs may also occur in patients with carotid stenosis and persistent vertebrobasilar connections or a fetal origin of the posterior cerebral artery.
IMAGING FINDINGS
Figure 1 (annotated) shows plaque in the proximal internal carotid artery (ICA), causing greater than 50% luminal narrowing on grayscale ultrasound. On the color Doppler images, there is evidence of color aliasing in the region of narrowing, with elevated velocities (Fig. 2). Figure 3 shows that the arterial waveforms distal to the region of narrowing are dampened, with a slow and weak systolic upstroke (tardus parvus) and spectral broadening.
On the computed tomography (CT) angiography in Figure 4, there is narrowing of the carotid bulb and origin of the proximal ICA by calcified and noncalcified atherosclerotic plaque. The degree of stenosis is calculated by dividing the diameter of the lumen at the site of greatest narrowing by the diameter of the uninvolved ICA beyond the stenosis.1
The three main sonographic criteria used to evaluate carotid stenosis are the peak systolic velocity (PSV) compared with the prestenotic velocity, the presence of plaque on grayscale imaging, and luminal narrowing by color Doppler.2 Doppler accuracy is related to the Doppler angle, with smaller angles creating smaller errors. The Doppler angle should be 60° or less and the protocol should be standardized to obtain the angle the same way in all patients to minimize errors in PSV measurement.3
Internal carotid dissection is caused by hemorrhage into the media of the vessel wall typically near the angle of the jaw (Fig. 5). The intimal flap is usually not visible and the false lumen frequently thrombosed. Doppler demonstrates a highly pulsatile signal with diminished diastolic flow. If the blood extends proximally enough, a thickened hypoechoic vessel wall may be seen, sometimes with luminal narrowing and focally elevated peak systolic velocities.4
5
Fig. 5: Carotid dissection following vomiting in 30-year-old eccentric circumferential hematoma in wall (arrows) narrows color lumen (in red) due to dissection propagating proximally from more distal break in wall.
Hematoma can be difficult to distinguish from noncalcified plaque. However, atherosclerosis is usually more heterogeneous in appearance and involves the carotid bulb, while dissection classically spares the carotid bulb.4 In cases where the false lumen is patent, reversed flow may be seen in the false lumen during certain phases of the cardiac cycle. While some dissections can be confidently diagnosed on ultrasound, CT or MR angiography can distinguish dissection from atherosclerotic narrowing with a greater degree of certainty.
MANAGEMENT
The management of symptomatic high-grade carotid artery stenosis (proximal ICA stenosis greater than 70%) is carotid endarterectomy (CEA). CEA in patients with symptomatic carotid stenosis has been shown to be superior to medical management when performed in centers with low mortality and morbidity.1 Carotid sonography is the most common study ordered prior to carotid endarterectomy, and some centers perform CEA solely on the results of the ultrasound.5 As a result, correct interpretation of the ultrasound is critical to avoid misdiagnosis and inappropriate therapy. CT or MR angiography may be performed in equivocal cases.
REFERENCES
- North American Symptomatic Carotid Endarterectomy Trial Collaborators. Benefit of Carotid Endarterectomy in Symptomatic Patients with High-grade Carotid Stenosis. New England Journal of Medicine. 1991;325:445–53.
- Grant E, Benson C, Moneta G, et al. Carotid artery stenosis: grayscale and Doppler US diagnosis—Society of Radiologists in Ultrasound Consensus Conference. Radiology. 2003;229:340–6.
- Logason K, Barlin T, Jonsson M, et al. The importance of Doppler angle of insonation on differentiation between 50-69% and 70-99% carotid artery stenosis. European Journal of Vascular and Endovascular Surgery. 2001;21:311–3.
- Rodallec M, Marteau V, Gerber S, et al. Craniocervical arterial dissection: spectrum of imaging findings and differential diagnoses. Radiographics. 2008;28:1711–28.
- Patel M, Greiner M, DiMartino L, et al. Geographic variation in carotid revascularization among medicare beneficiaries, 2003-2006. Archives of Internal Medicine. 2010;170:1218–25.