Carotid web

Carotid webs, also known as carotid intimal variant fibromuscular dysplasia, are rare vascular anomaliespathologies of the internal carotid artery that are an important cause of cryptogenic and recurrent ischaemic stroke.

Epidemiology

Carotid webs are thought to be very rare, with two case series finding only 1.0-1.2% of patients who underwent CT angiogram for suspected ischaemic stroke had radiographic evidence of carotid web ^1,2.

Clinical presentation

Carotid webs clinically manifest as either recurrent ischaemic stroke or recurrent transient ischaemic attack ^1-3, with one study finding that recurrence rate of ischaemic stroke was as high as 29% ³. They are otherwise asymptomatic ^1-3.

Pathology

A carotid web is defined as a thin, linear, membrane that extends from the posterior aspect of the internal carotid artery bulb into the lumen, located just beyond the carotid bifurcation ^1-3. Histologically, it is thought be a rare variant of fibromuscular dysplasia, thus it is also referred to as 'intimal variant' fibromuscular dysplasia ^1-3.

Carotid webs are highly thrombogenic and may be implicated in ischaemic stroke ^1-3. This occurs due to stasis of blood that occurs just distal to the web, resulting in thrombus formation, which can then embolise intracranially ¹.

Radiographic features

In one study, approximately one-quarter of carotid webs detected radiographically were thrombosed, and just over half of all patients had bilateral carotid webs ³. Importantly, other radiographic evidence of fibromuscular dysplasia is often not appreciated.

Ultrasound

Carotid webs may be detectable as echogenic lesions on routine carotid Doppler ultrasound ^4,5, but this imaging modality is not considered to be as reliable as CT angiography or DSA ^2,5. There may or may not be haemodynamically significant stenosis accompanying a carotid web ^4,5.

CT

CT angiography is most commonly used to detect and evaluate carotid webs ^1-3,5,6. In particular, thin axial and oblique sagittal views are most useful ^1-3,5,6. Radiographically, carotid webs are typically described as shelf-like, linear, thin, smooth filling defects, located along the posterior wall of the internal carotid artery bulb, just beyond the carotid bifurcation ^1-3,5,6. 

MRI

Findings on MR angiography are identical to those seen in CT angiography ².

DSA

Digital subtraction angiography is considered the gold-standard imaging modality for detecting carotid webs, whereby contrast is seen to pool in the web, even in venous phases ³. However, itDSA is less accessible than CT or MR angiography and carries inherent risks, and thus is not routinely a first-line imaging investigation ³.

Treatment and prognosis

Given high risk of recurrent ischaemic stroke, management of carotid webs is important. Management options include pharmacological therapy, such as use of antiplatelet agents, or surgical therapy, such as carotid stenting or endarterectomy ². Although evidence is limited, one study found that rates of ischaemic stroke were lower in patients given surgical therapy when compared to a group given only pharmacological therapy ^2,7.