Carotid Web 🧵🧠

A carotid web is a shelf-like projection of fibrous intimal tissue into the lumen of the carotid bulb, usually on the posterior wall of the proximal internal carotid artery (ICA). It is a non-atherosclerotic lesion, probably within the spectrum of intimal fibromuscular dysplasia (FMD), and an under-recognised cause of embolic ischaemic stroke – especially in younger patients with few traditional risk factors.

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1️⃣ Definition & Pathology

• Thin, triangular / shelf-like intimal thickening projecting into the carotid bulb lumen.
• Most often on the posterior wall of the proximal ICA just beyond the bifurcation.
• Histology: fibrous intimal proliferation with minimal lipid, inflammation or calcification (unlike atherosclerosis).
• Considered a focal form of intimal FMD rather than typical medial FMD (string-of-beads).

💡 Think of a carotid web as a little fibrous ledge in the carotid bulb that disrupts flow, promotes thrombus formation, and embolises to the brain.

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2️⃣ Epidemiology & Clinical Context

• Rare in the general population, but enriched among:
  • Young or middle-aged stroke patients (<60 years).
  • Minimal or no traditional vascular risk factors.
  • Cryptogenic or ESUS (embolic stroke of undetermined source).
• Often identified on the side of an embolic-appearing MCA/ACA infarct (cortical, wedge-shaped, multiple territories).
• May be bilateral but typically only one side is symptomatic.
• More frequently reported in women and in some ethnic groups (e.g. Black patients) in case series.

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3️⃣ Pathophysiology – Why Does It Cause Stroke?

• The web creates a localised flow disturbance in the carotid bulb:
  • Flow separation and recirculation distal to the ledge.
  • Low shear, high residence time zone behind the web.
  • Predisposition to mural thrombus forming along or just distal to the web.
• Thrombus fragments can embolise distally to:
  • M1/M2 branches of the MCA,
  • ACA territory, or
  • Anterior choroidal / ophthalmic artery.
• Stroke pattern is typically artery-to-artery embolic:
  • Cortical infarcts, often wedge-shaped.
  • Multiple small cortical/subcortical lesions in the same vascular territory.
• Unlike atheroma, there is usually little or no luminal stenosis by NASCET criteria; risk is about thrombus, not tight narrowing.

🧬 Conceptual model: structural ledge → abnormal flow → mural thrombus → embolic stroke, often in a young otherwise “low risk” patient.

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4️⃣ Imaging – How Do You Spot a Carotid Web?

🩻 CT Angiography (CTA) – Modality of Choice

• Best seen on oblique sagittal and multiplanar reconstructions through the carotid bulb.
• Appears as:
  • A thin, triangular or shelf-like filling defect on the posterior wall of the ICA bulb.
  • Often pointing into the lumen with a smooth surface and no calcification.
  • Little overall narrowing of the lumen (<50% stenosis usually).
• Look carefully in patients labelled “normal carotids” on axial-only review – webs are easy to miss.

🧲 MR Angiography (MRA)

• Can show a similar shelf-like defect, but spatial resolution is lower than CTA.
• High-resolution vessel wall MRI can demonstrate focal intimal thickening without lipid-rich plaque.

🩺 Duplex Ultrasound

• May show a small intraluminal shelf at the bulb with:
  • Local flow disturbance or eddies.
  • Subtle, focal colour Doppler aliasing.
• Operator dependent; webs can be overlooked or mislabelled as minor plaque.

🧪 Catheter Angiography

• Classically shows a linear filling defect along the posterior bulb wall, best in oblique projections.
• Rarely first-line now but may be used when planning stenting or endarterectomy.

🔍 Radiology tip: when reviewing CTA in a young cryptogenic stroke, scroll slowly through thin-slice sagittal views of the carotid bulb – ask yourself “is there a tiny posterior shelf?”

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5️⃣ Clinical Presentation – When Should You Suspect It?

• Young / middle-aged patient with:
  • Anterior circulation ischaemic stroke or TIA, often cortical.
  • “Cryptogenic” label after standard work-up (no AF, no major plaque, normal echo, no PFO or prothrombotic state).
• Stroke pattern on MRI:
  • Embolic distribution in MCA/ACA territory.
  • Sometimes recurrent infarcts in the same territory.
• CTA shows a posterior bulb shelf ipsilateral to the infarcts.

💡 Stroke clinic mindset: in a young “cryptogenic” MCA stroke, actively look for carotid web, dissection, PFO and FMD – don’t stop at “no AF, no plaque”.

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6️⃣ Natural History & Stroke Risk

• Observational cohorts suggest a high risk of recurrent events on medical therapy alone (antiplatelets), with recurrence rates of ~20–30% or higher in some series over 1–2 years.
• Recurrent events are usually ipsilateral embolic strokes or TIAs.
• After carotid endarterectomy or stenting, reported recurrence rates are much lower, but data are from small, non-randomised series.
• No large RCTs yet; management is guided by expert opinion and case series rather than high-level evidence.

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7️⃣ Management – Current Practice (No Formal Guidelines Yet)

🧪 Medical Therapy

• Antiplatelet therapy (e.g. aspirin or clopidogrel) plus aggressive vascular risk factor control.
• Some centres consider anticoagulation (DOAC/warfarin) in selected patients, though evidence is limited.
• Problem: several series report substantial stroke recurrence on medical therapy alone.

🩻 Carotid Intervention

• Carotid endarterectomy (CEA)
  • Surgical removal of the web and any adherent thrombus.
  • Provides tissue for histology (confirming intimal FMD/web).
• Carotid artery stenting (CAS)
  • Endovascular option; stent “pins” the web against the wall and alters local flow.
  • Attractive in younger patients and where surgical access is difficult.
• Series and systematic reviews suggest that in symptomatic webs:
  • CEA and CAS both have low peri-procedural complication rates.
  • Recurrent stroke/TIA after intervention appears very low compared with medical therapy alone.

🇬🇧 Practical UK/Europe Approach (Evolving)

• Consider carotid web in the differential of ESUS in younger patients.
• Discuss symptomatic webs in an MDT involving stroke, vascular surgery and interventional neuroradiology.
• Favour intervention (CEA or CAS) for:
  • Recurrent ipsilateral events despite optimal medical therapy, or
  • First event in high-risk young patient where anatomically suitable and MDT agrees.
• Continue long-term antiplatelet therapy after intervention, as per local carotid practice.

⚖️ Key teaching point: unlike atherosclerotic 40–50% stenosis, a symptomatic carotid web may justify intervention even without high-grade stenosis, because the mechanism is embolic from thrombus on the web.

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8️⃣ Carotid Web vs Atherosclerotic Carotid Stenosis

Feature	Carotid Web	Atherosclerotic Stenosis
Typical age	Younger / middle-aged, often <60	Older adults with classic vascular risk factors
Risk factors	Often few; may coexist with FMD	HTN, diabetes, hyperlipidaemia, smoking
Histology	Intimal fibrous shelf, non-atheromatous	Lipid-rich necrotic core, fibroatheroma, calcification
Imaging appearance	Thin posterior shelf in bulb; minimal stenosis	Eccentric plaque, concentric narrowing; % stenosis measurable
Stroke mechanism	Artery-to-artery embolism from thrombus on web	Embolism from plaque or haemodynamic low-flow past critical stenosis
Guideline status	No dedicated RCT-based guidance yet	Clear thresholds for CEA/CAS in symptomatic ≥50–70% stenosis

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9️⃣ OSCE & Exam Pearls 🎓

• Define a carotid web as a thin, shelf-like intimal protrusion in the carotid bulb, considered a subtype of intimal FMD and an important cause of embolic stroke in younger patients.
• Remember CTA in oblique sagittal MPR is the key diagnostic imaging – look for a posterior shelf with little overall narrowing.
• Emphasise that recurrent stroke risk with medical therapy alone can be high, so MDT discussion about CEA/CAS is appropriate in symptomatic cases.
• Contrast with atherosclerotic stenosis: different age group, histology, and decision-making (risk from thrombus on web, not degree of stenosis).

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🔟 Take-Home Messages

• Carotid web is a rare but important, underdiagnosed cause of embolic stroke, mainly in younger patients with otherwise normal arteries.
• Mechanism is local flow disturbance → mural thrombus → artery-to-artery embolism.
• CTA with careful bulb review is essential; webs are easily missed on axial images alone.
• Medical therapy alone may leave a substantial residual stroke risk; CEA or CAS appears highly effective in small series but lacks RCT confirmation.
• Always think of carotid web in a young ESUS/cryptogenic stroke with ipsilateral carotid “abnormality” that doesn’t look like plaque.