Carotid webs, also known as carotid intimal variant fibromuscular dysplasia, are rare vascular pathologies of the internal carotid artery that are an important cause of cryptogenic and recurrent ischemic stroke.
Carotid webs have had many different names in the literature, including carotid weblike formations or septums, carotid pseudovalvular folds, carotid shelves, carotid diaphragms, and thrombotic carotid megabulbs 10. 'Carotid web' is the most widely used description 10.
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 ischemic stroke had radiographic evidence of carotid web 1,2.
Carotid webs clinically manifest as either recurrent ischemic stroke or recurrent transient ischemic attack 1-3, especially in young patients, with one study finding that recurrence rate of ischemic stroke was as high as 29% 3. They are otherwise asymptomatic 1-3.
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 ischemic stroke 1-3. This occurs due to stasis of blood just distal to the web, resulting in thrombus formation, which can then embolize intracranially 1.
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.
Carotid webs may be detectable as echogenic lesions on routine carotid Doppler ultrasound 4,5,10, but this imaging modality is not considered to be as reliable as CT angiography, MR angiography or DSA 2,5,10. There may or may not be haemodynamically significant stenosis accompanying a carotid web 4,5,10.
CT angiography is most commonly used to detect and evaluate carotid webs 1-3,5,6,10. In particular, thin axial and oblique sagittal views are most useful 1-3,5,6,10. 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 1-3,5,6,10.
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. Although this classic finding may not be appreciated on standard posteroanterior or lateral DSA projections, and oblique projections may be required 10.
However, DSA is less accessible and more invasive than CT or MR angiography and carries inherent risks, thus is not routinely a first-line imaging investigation 3.
Treatment and prognosis
Given high risk of recurrent ischemic stroke, appropriate 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 ischemic stroke were lower in patients given surgical therapy when compared to a group given only pharmacological therapy 2,7.
History and etymology
The first description was in 1968 by Rainer et al. 8, although the term 'web' was first used in 1973 by Momose and New 9.
- spontaneous internal carotid artery dissection flap
- dissection is generally more distal along the internal carotid artery, has more irregular borders, and may cause increase in the arterial diameter from pseudoaneurysm 10
- atherosclerotic plaque
- tends to have more irregular borders, may also be distal to the internal carotid bulb, and may have associated calcifications 10
- 1. Choi PM, Singh D, Trivedi A, Qazi E, George D, Wong J, Demchuk AM, Goyal M, Hill MD, Menon BK. Carotid Webs and Recurrent Ischemic Strokes in the Era of CT Angiography. (2015) AJNR. American journal of neuroradiology. 36 (11): 2134-9. doi:10.3174/ajnr.A4431 - Pubmed
- 2. Jonathan M. Coutinho, Sheldon Derkatch, Alphonse R.J. Potvin, George Tomlinson, Leanne K. Casaubon, Frank L. Silver, Daniel M. Mandell. Carotid artery web and ischemic stroke. (2017) Neurology. 88 (1): 65. doi:10.1212/WNL.0000000000003464 - Pubmed
- 3. Haussen DC, Grossberg JA, Bouslama M, Pradilla G, Belagaje S, Bianchi N, Allen JW, Frankel M, Nogueira RG. Carotid Web (Intimal Fibromuscular Dysplasia) Has High Stroke Recurrence Risk and Is Amenable to Stenting. (2017) Stroke. 48 (11): 3134-3137. doi:10.1161/STROKEAHA.117.019020 - Pubmed
- 4. Kliewer MA, Carroll BA. Ultrasound case of the day. Internal carotid artery web (atypical fibromuscular dysplasia). (1991) Radiographics : a review publication of the Radiological Society of North America, Inc. 11 (3): 504-5. doi:10.1148/radiographics.11.3.1852941 - Pubmed
- 5. Fu W, Crockett A, Low G, Patel V. Internal Carotid Artery Web: Doppler Ultrasound with CT Angiography correlation. (2015) Journal of radiology case reports. 9 (5): 1-6. doi:10.3941/jrcr.v9i5.2434 - Pubmed
- 6. Sajedi PI, Gonzalez JN, Cronin CA, Kouo T, Steven A, Zhuo J, Thompson O, Castellani R, Kittner SJ, Gandhi D, Raghavan P. Carotid Bulb Webs as a Cause of “Cryptogenic” Ischemic Stroke. (2017) American Journal of Neuroradiology. 38 (7): 1399. doi:10.3174/ajnr.A5208 - Pubmed
- 7. Gupta A, Baradaran H, Kamel H, Pandya A, Mangla A, Dunning A, Marshall RS, Sanelli PC. Evaluation of computed tomography angiography plaque thickness measurements in high-grade carotid artery stenosis. (2014) Stroke. 45 (3): 740-5. doi:10.1161/STROKEAHA.113.003882 - Pubmed
- 8. Rainer WG, Cramer GG, Newby JP, Clarke JP. Fibromuscular hyperplasia of the carotid artery causing positional cerebral ischemia. (1968) Annals of surgery. 167 (3): 444-6. Pubmed
- 9. Momose KJ, New PF. Non-atheromatous stenosis and occlusion of the internal carotid artery and its main branches. (1973) The American journal of roentgenology, radium therapy, and nuclear medicine. 118 (3): 550-66. Pubmed
- 10. Kim SJ, Nogueira RG, Haussen DC. Current Understanding and Gaps in Research of Carotid Webs in Ischemic Strokes: A Review. (2018) JAMA Neurology. doi:10.1001/jamaneurol.2018.3366