Chapter 24

### PATIENT STORY

A 50-year-old man presented with a 1-year history of worsening fatigue and bitemporal headaches. He denied focal neurologic symptoms, but complained of constant dizziness which was exacerbated when he went from a lying to a standing position. Sometimes he experienced syncopal episodes, and a complete syncope workup thus far had been negative. Carotid duplex ultrasound suggested chronic occlusion of his left internal carotid artery (ICA), with a 70% to 99% stenosis of his right ICA. Carotid duplex ultrasound also showed elevated velocities in his external carotid arteries (ECAs) bilaterally indicating significant stenosis.

### EPIDEMIOLOGY

• Symptomatic ICA occlusion has an incidence of 6 per 100,000, though the rate of asymptomatic chronic occlusion is unknown and may be higher.1

### ETIOLOGY AND PATHOPHYSIOLOGY

• Total ICA occlusion results from thrombosis of or embolization to the cervical carotid in the setting of chronic stenosis. Cardiogenic embolization to a normal carotid bifurcation or carotid dissection may also cause total occlusion of the ICA.

• Acute occlusion may result in a carotid territory stroke.

• A previously asymptomatic chronic ICA occlusion may become symptomatic related to embolic or hemodynamic issues.

• Embolism may occur from the ipsilateral ECA via collaterals to the cerebral circulation. It may also occur when there is occult patency of the occluded ICA, which then serves as the source of embolic material.

• Hemodynamic insufficiency may occur when any condition that interferes with cerebral perfusion such as orthostasis, hypotension, volume depletion, or cardiac failure is superimposed on the carotid occlusion, especially when contralateral carotid disease is significant (Figure 24-1).2

###### FIGURE 24-1

Occlusion of the internal carotid artery (ICA) results in collateral formation via the external carotid artery (ECA).

### CLINICAL FEATURES

• The distinction between hemodynamic and embolic stroke in the setting of chronic ICA occlusion is important.

• Embolic symptoms are those of classic stroke or transient ischemic attack (TIA) and typically are focal. They may include contralateral motor or sensory deficits or amaurosis.

• Hemodynamic symptoms may be similar to those of classic stroke or TIA, but may also be less predictable and atypical.

• Symptoms such as limb shaking, retinal claudication, headache from large pulsatile ECA collaterals, syncope, and generalized fatigue have all been reported.2

### DIAGNOSIS

• Carotid duplex ultrasound examination typically shows a high-resistant signal in the carotid bulb and the very proximal ICA (Figure 24-2). Distally, there are no Doppler signals audible in the carotid artery.

• Some form of contrast examination such as digital subtraction arteriography, magnetic resonance arteriography (MRA), or computed tomographic (CT) arteriography is generally required to confirm the diagnosis (Figure 24-3).

###### FIGURE 24-2

Occlusion of the distal internal carotid artery (ICA) results in a high-resistance Doppler waveform when the vessel is interrogated ...

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