Carotid Artery Stenosis

Atherosclerotic Plaque Formation and Evolution

• Endothelial injury occurs at regions of low shear stress (carotid bifurcation), allowing LDL infiltration and oxidation
• Oxidized LDL triggers inflammatory cascade with monocyte recruitment and foam cell formation, establishing fatty streak
• Smooth muscle cell migration from media into intima, with collagen and proteoglycan deposition, creates fibrous cap over lipid core
• Chronic inflammation and plaque remodeling with matrix metalloproteinase (MMP) activation progressively narrow the arterial lumen

Thromboembolism Mechanisms

• Plaque rupture or erosion exposes tissue factor-rich lipid core, triggering coagulation cascade and platelet aggregation
• Microemboli formation releases cholesterol crystals, platelet aggregates, and fibrin directly into distal circulation, causing embolic stroke
• Red thrombus formation on ulcerated plaque surface with concurrent arterial stenosis promotes stasis and coagulation
• Activated platelets release serotonin, thromboxane A2, and ADP, amplifying thrombotic potential

Hemodynamic Insufficiency

• Severe stenosis (>90% diameter reduction) reduces distal pressure and cerebral perfusion pressure, particularly during systemic hypotension or increased metabolic demand
• Borderzone ischemia develops in territories between major vascular distributions when collateral circulation is inadequate
• Paradoxical embolism risk increases when ipsilateral carotid occlusion forces flow reversal in anterior communicating artery

Plaque Characteristics Predicting Instability

• Intraplaque hemorrhage with macrophage infiltration and thin fibrous caps (<65 μm) indicate high-risk morphology
• Calcification paradoxically increases plaque stiffness and rupture risk despite stabilizing effect on fibrous cap
• Large necrotic core (>40% plaque volume) correlates with symptomatic presentation

Primary Cause

• Atherosclerotic disease accounts for >90% of CAS, typically affecting the proximal internal carotid artery within 2 cm of the bifurcation

Major Modifiable Risk Factors

• Hypertension (present in 75% of patients) accelerates atherosclerotic progression through endothelial shear stress
• Tobacco use (current or former in 70%) increases plaque inflammation and instability
• Hyperlipidemia (LDL >100 mg/dL) directly correlates with atherosclerotic burden
• Diabetes mellitus (2-3 fold increased risk) promotes glycation of plaque proteins and endothelial dysfunction
• Physical inactivity and obesity increase systemic inflammation and metabolic syndrome components

Non-Modifiable Risk Factors

• Advanced age (risk increases exponentially after age 60)
• Male sex (male predominance 3-4:1)
• Family history of premature atherosclerotic disease or stroke

Non-Atherosclerotic Causes (Rare)

• Arterial dissection (spontaneous or trauma-related) in younger patients; characterized by intimal tear
• Vasculitis (Takayasu arteritis, giant cell arteritis, SLE) causing inflammatory narrowing
• Fibromuscular dysplasia with characteristic "beads-on-string" appearance
• Radiation-induced stenosis from prior head/neck radiation therapy
• Thromboembolism from cardioembolism or paradoxical embolism with in situ thrombosis

Symptomatic Presentations

• Transient ischemic attack (TIA) with sudden onset amaurosis fugax (monocular vision loss) or contralateral motor/sensory deficits lasting <24 hours
• Acute ischemic stroke with persistent focal neurologic deficits (contralateral hemiplegia, hemisensory loss, aphasia if dominant hemisphere, hemianopia)
• Retinal artery occlusion causing sudden painless monocular vision loss with retinal whitening and cherry-red spot on fundoscopy
• Recurrent stereotyped TIAs suggest hemodynamic insufficiency from high-grade stenosis

Asymptomatic Presentations

• No prior neurologic events despite imaging evidence of significant stenosis (often incidental finding on imaging for other indications)
• May have subtle cognitive decline or gait disturbance unrecognized by patient

Physical Examination Findings

• Carotid bruit (systolic or systolic-diastolic) heard on carotid auscultation, indicating turbulent flow; absence does not exclude stenosis, and presence alone does not indicate hemodynamically significant disease
• Diminished carotid pulse or reduced carotid pulsatility on palpation, suggesting tight stenosis
• Ipsilateral Horner syndrome may develop with severe stenosis affecting sympathetic fibers in carotid sheath
• Focal neurologic deficits consistent with territory of involved vessel (hemispheric vs. retinal symptoms)

Clinical Suspicion Index

• Recent TIA or stroke in appropriate vascular territory
• Asymptomatic carotid bruit detected on routine examination
• Age >60 with vascular risk factors

Carotid Duplex Ultrasound (First-Line Imaging)

• Peak systolic velocity (PSV) interpretation: Normal <125 cm/s; 50-69% stenosis = PSV 125-230 cm/s; ≥70% stenosis = PSV >230 cm/s; occlusion = no Doppler signal
• End-diastolic velocity (EDV) aids stratification (EDV >100 cm/s suggests ≥70% stenosis)
• Plaque morphology assessment: Echolucent (lipid-rich, unstable) vs. echogenic (calcified, stable) plaques; ulceration indicates higher embolic risk
• Vertebral artery assessment for bilateral disease evaluation
• Limitations: operator-dependent; difficulty in very obese patients or in presence of severe calcification; limited in posterior circulation assessment

CT Angiography (CTA) - Excellent Alternative

• Sensitivity 94-98% and specificity 93-96% for ≥50% stenosis
• Advantages: rapid acquisition, excellent visualization of calcified plaque and ulceration, whole-neck imaging, assessment of contralateral and vertebral vessels
• Limitations: radiation exposure, contrast nephropathy risk, less dynamic information than ultrasound
• Measurement: North American Symptomatic Carotid Endarterectomy Trial (NASCET) method: percentage stenosis = (1 - [minimal lumen diameter/distal normal internal carotid diameter]) × 100

MR Angiography (MRA)

• Sensitivity 90-94% and specificity 85-95% for severe stenosis
• Advantages: no ionizing radiation, excellent soft tissue contrast, better for detecting dissection
• Limitations: overestimates severity due to signal loss in turbulent flow; contrast-enhanced preferred over time-of-flight; gadolinium contraindicated in severe renal disease (nephrogenic systemic fibrosis risk)

Cerebral Digital Subtraction Angiography

• Gold standard for stenosis quantification (reference standard for clinical trials)
• Indications: diagnostic uncertainty, planning for endovascular intervention, preoperative assessment before carotid endarterectomy
• Risks: 0.1-0.5% major stroke risk, 0.1% mortality; reserved for therapeutic intent

Laboratory and Additional Testing

• Fasting lipid panel, glucose, CBC, coagulation studies to assess global cardiovascular risk and identify modifiable factors
• ECG and cardiac imaging to exclude cardioembolic source in stroke patients
• Brain MRI or CT to determine infarct age and location; diffusion-weighted imaging (DWI) determines acute vs. chronic stroke

Diagnostic Criteria for Severity (NASCET methodology)

• <50% stenosis: low stroke risk; manage medically
• 50-69% stenosis: moderate risk; ultrasound confirmation and intensive medical therapy recommended
• ≥70% stenosis (symptomatic): high risk (13-26% 2-year stroke risk); intervention consideration
• ≥80% stenosis (asymptomatic): moderate risk (5% annual stroke risk); individualized intervention decision

Medical Therapy (All Patients)

Antiplatelet Agents - First-Line

• Aspirin (75-325 mg daily) irreversibly inhibits platelet COX-1, preventing TXA2 synthesis; dose ≥300 mg loading dose for acute stroke; NNT = 67 for one stroke prevention over 2 years
• Clopidogrel (75 mg daily, 600 mg loading dose) blocks P2Y12 ADP receptor; indicated in aspirin allergy or intolerance; similar efficacy to aspirin monotherapy
• Aspirin-extended-release dipyridamole (25/200 mg twice daily) provides modest additional benefit over aspirin alone in secondary stroke prevention (NNT = 25 over 2 years)
• Dual antiplatelet therapy (aspirin + clopidogrel) for 3 months following acute TIA or stroke, then monotherapy

Statin Therapy - Cornerstone

• Atorvastatin (40-80 mg daily) or rosuvastatin (20-40 mg daily) shown to reduce stroke risk by ~20% and promote plaque stabilization
• Target LDL <70 mg/dL in secondary prevention; consider <55 mg/dL in very high-risk patients
• Mechanism: reduced inflammation, improved endothelial function, plaque stabilization through increased fibrous cap thickness
• High-intensity statin mandatory regardless of baseline lipid levels

Blood Pressure Control

• Target BP <130/80 mmHg in secondary stroke prevention (evidence supports systolic target of 120 mmHg in select populations)
• ACE inhibitors (e.g., lisinopril 10-40 mg daily) preferred in post-stroke setting for neuroprotection and plaque stabilization
• Calcium channel blockers or thiazide diuretics as alternatives
• Avoid aggressive lowering in acute phase (risk of watershed infarction)

Glycemic Control

• Diabetes management with target HbA1c 7-8% reduces microvascular complications; intensive control (<7%) may increase hypoglycemic events
• Metformin (1000-2000 mg daily) preferred first-line agent (cardiovascular benefits, weight neutral, no lactic acidosis at normal renal function)

Lifestyle Modifications

• Smoking cessation is single most impactful intervention; reduces stroke risk by 50% within 1 year
• Mediterranean diet with emphasis on fruits, vegetables, whole grains, olive oil
• Aerobic exercise 150 minutes/week moderate-intensity activity
• Weight loss target BMI 18.5-24.9 kg/m²
• Alcohol moderation <2 drinks/day for men

Surgical Intervention: Carotid Endarterectomy (CEA)

Symptomatic Stenosis ≥70% (NASCET Criteria)

• Absolute indication for CEA if patient within 2 weeks of symptoms and acceptable surgical risk (operative risk <3% for death/stroke)
• Number needed to treat (NNT) = 5 for one ipsilateral stroke prevention over 2 years
• CEA superior to medical therapy alone in this population
• Timing: ideally within 2 weeks of symptom onset; benefit persists up to 6 months but decreases with time

Symptomatic Stenosis 50-69%

• Individualized decision based on patient age, gender, comorbidities, and plaque morphology
• Young patients and those with unstable plaques benefit more
• CEA consideration if high-risk features present

Asymptomatic Stenosis ≥80%

• Individualized based on life expectancy, perioperative risk, and patient preference
• Reasonable consideration if contralateral carotid normal and patient age <75 with <3% operative risk
• Annual stroke risk 1-2% with medical therapy alone in asymptomatic severe stenosis
• NNT = 30-50 for one stroke prevention, making surgery less compelling than symptomatic disease

Surgical Technique

• Standard CEA involves arteriotomy, plaque removal, and closure (primary or with patch)
• Shunting during surgery considered if intolerance to clamping identified preoperatively or via electroencephalography
• Local vs. general anesthesia both acceptable; some evidence for better outcomes with local (allows neuromonitoring)

Perioperative Complications

• Stroke/TIA: 2-3% major perioperative event rate within 30 days
• Myocardial infarction: 1-2% perioperative risk
• Hyperperfusion syndrome: delayed (2-14 days post-op) with headache, seizures, intracerebral hemorrhage from sudden increase in cerebral perfusion
• Cranial nerve injury: hypoglossal nerve (tongue deviation), vagus nerve (hoarseness), facial nerve (rare)

Carotid Artery Stenting (CAS)

Indications

• Symptomatic or asymptomatic stenosis with recurrent symptoms despite maximal medical therapy
• High surgical risk patients (unstable angina, recent MI, severe COPD, prior radical neck surgery, radiated neck, contralateral vocal cord paralysis)
• Tandem lesions or inaccessible lesions
• Failed CEA or restenosis

Technique and Risks

• Endovascular approach with embolic protection device (EPD) placed distally to catch debris during intervention
• Perioperative stroke/death risk: 4-6% in symptomatic patients, higher in elderly and women
• Restenosis rate: 6-10% at 1 year (higher than CEA)
• Distal embolization remains significant risk despite EPDs

Evidence and Comparison to CEA

• CREST trial (Carotid Revascularization Endarterectomy versus Stenting Trial): equivalent 2-year outcomes for symptomatic disease; CEA favored in patients ≥70 years (higher CAS stroke risk)
• CAS preferred in selected high-risk surgical patients with acceptable anatomy

Monitoring Post-Intervention

• Duplex ultrasound at 1 month, 6 months, 1 year, then annually for both CEA and CAS
• Progressive restenosis (intimal hyperplasia after CEA or in-stent restenosis after CAS) assessed by PSV criteria
• Target PSV <125 cm/s at each follow-up

Perioperative and Acute Complications

Stroke/TIA

• Intraoperative: from carotid clamping, emboli during plaque removal, or shunt malposition
• Postoperative: thrombus at surgical site, distal embolization, or watershed infarction
• Management: urgent imaging (CT/MRI); anticoagulation if non-hemorrhagic; consider recatheterization for acute thrombosis or reintervention

Hyperperfusion Syndrome

• Pathophysiology: chronic hypoperfusion impairs autoregulation; sudden restoration of perfusion causes vasodilation and capillary leak

Buzzwords that give away the diagnosis

• Amaurosis fugax: painless monocular visual loss described as a shade or curtain descending, from an embolus to the ophthalmic artery — the eye is ipsilateral to the diseased carotid, while motor/sensory deficits are contralateral. This laterality flip is the single most tested point.
• Hollenhorst plaque: bright, refractile cholesterol crystal lodged at a retinal arteriolar bifurcation on fundoscopy — proof of an aortocarotid embolic source, not a reason to anticoagulate.
• Bilateral or crossed findings (vertigo, diplopia, dysarthria, ataxia) point to vertebrobasilar disease, not the carotid; do not order a carotid intervention for these.

Best next step

• Carotid duplex ultrasound is the initial test after a hemispheric TIA, retinal ischemia, or minor stroke; CTA/MRA confirms before any revascularization.
• Every patient gets antiplatelet therapy plus a high-intensity statin and risk-factor control, whether or not they are revascularized — the AHA/ASA secondary stroke prevention guideline frames medical therapy as universal, revascularization as additive.

The association examiners test

• Symptomatic stenosis ≥70% with acceptable surgical risk → carotid endarterectomy, ideally within about 2 weeks of the index event (AHA/ASA). Delay squanders the period of highest recurrence risk.

Distractors to avoid

• An asymptomatic carotid bruit is not an indication to screen or operate. The USPSTF gives screening for asymptomatic carotid stenosis in the general adult population a grade D recommendation; bruits are neither sensitive nor specific, and a critically stenotic vessel may be silent.
• Complete occlusion is not revascularized — endarterectomy benefits stenosis, not a chronically occluded vessel.
• CREST: stenting carried more periprocedural stroke and endarterectomy more periprocedural MI; older patients fare better with endarterectomy.
• Hyperperfusion syndrome: unilateral headache, seizure, or intracerebral hemorrhage days after revascularization from lost autoregulation — treat with blood pressure control, not thrombolysis.
• Hypoglossal nerve injury after endarterectomy: tongue deviates toward the injured side.