A 68-year-old man with hypertension, dyslipidemia, and 20 pack-year smoking history presents with a 2-week history of transient monocular blindness in the left eye. Carotid duplex ultrasound is performed. The structure marked **B** in the diagram shows a hypoechoic, heterogeneous plaque with surface ulceration at the left carotid bifurcation, with peak systolic velocity of 185 cm/s. Which of the following best explains why this patient is at HIGH RISK for ipsilateral ischemic stroke despite moderate stenosis?

Question

Accepted Answer

D. Vulnerable plaque morphology with thin fibrous cap, large lipid-rich necrotic core, and surface ulceration predisposes to artery-to-artery thromboembolism from plaque rupture and debris shedding. ## Why option 1 is correct

The clinical anchor is that **vulnerable plaque morphology** — characterized by thin or ruptured fibrous cap, large lipid-rich necrotic core, intraplaque hemorrhage, and surface ulceration — confers HIGH STROKE RISK through **artery-to-artery embolism** from plaque debris and thrombus, **independent of stenosis severity**. The structure marked **B** (vulnerable carotid plaque, hypoechoic + ulcerated) exemplifies this high-risk phenotype. The patient's amaurosis fugax (transient monocular blindness from retinal artery embolism) is the clinical manifestation of this embolic mechanism. Per AHA/ASA guidelines and NASCET/ACST trials, plaque vulnerability — not stenosis percentage alone — drives stroke risk stratification. This patient's moderate stenosis (PSV 185 cm/s ≈ 50–69%) would normally confer modest risk, but the vulnerable morphology elevates him to high-risk status requiring urgent intervention (CEA within 2 weeks for symptomatic disease).

## Why each distractor is wrong

- **Option 2**: Moderate stenosis (50–69%) alone does NOT cause hemodynamic flow-limiting ischemia; symptomatic strokes in this range are due to **embolic mechanisms** (plaque rupture, thrombus shedding), not flow limitation. Flow-limiting ischemia occurs with severe stenosis (>90%) or near-occlusion.
- **Option 3**: Hypoechoic appearance indicates **lipid/hemorrhage content** (vulnerable plaque), NOT calcification. Calcified plaques are **hyperechoic** with posterior shadowing and are more stable. This distractor reverses the ultrasound morphology-risk relationship.
- **Option 4**: Amaurosis fugax is a **symptom of embolic stroke**, not a contraindication to intervention. It is, in fact, a strong indication for urgent CEA (within 2 weeks) in symptomatic carotid stenosis ≥50%. Anticoagulation alone is not standard; CEA is the definitive management for symptomatic disease.

**High-Yield:** Vulnerable carotid plaque (hypoechoic, ulcerated, lipid-rich) causes stroke via **artery-to-artery embolism regardless of stenosis severity**; plaque morphology, not stenosis % alone, determines stroke risk.

[cite: AHA/ASA Carotid Stenosis Guidelines; NASCET; ACST trials; Carotid duplex ultrasound interpretation per ACC/AHA imaging standards]

Answer

A. Moderate stenosis (50–69% by NASCET criteria) alone is sufficient to cause hemodynamic compromise and flow-limiting ischemia in the ipsilateral hemisphere

Answer

B. Amaurosis fugax is a contraindication to carotid intervention and indicates that the plaque has already embolized, making further stroke inevitable without anticoagulation

Answer

C. The hypoechoic appearance on ultrasound indicates calcification and plaque stability, which paradoxically increases embolic risk through increased plaque rigidity

Explanation

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