A 58-year-old woman presents to the emergency department with acute onset dyspnea and pleuritic chest pain for 6 hours. She returned from a 12-hour flight 2 days ago. Vital signs: HR 110 bpm, BP 128/82 mmHg, RR 24/min, SpO₂ 91% on room air. D-dimer is elevated at 2.8 μg/mL. CT pulmonary angiography (CTPA) is performed and shows a filling defect in the right lower lobe segmental pulmonary artery with no evidence of right ventricular dilatation. What is the most appropriate interpretation of this finding?

Explanation

## CT Pulmonary Angiography (CTPA) Interpretation ### Clinical Context The patient has classic risk factors for venous thromboembolism (recent long-haul flight, acute dyspnea, elevated D-dimer) and imaging findings consistent with acute PE. ### Key Imaging Finding **Key Point:** A filling defect in a segmental pulmonary artery represents a segmental-level PE, which is hemodynamically significant and requires anticoagulation. ### Significance of Segmental PE | Feature | Subsegmental PE | Segmental PE | Lobar PE | |---------|-----------------|--------------|----------| | **Vessel caliber** | <2 mm | 2–4 mm | >4 mm | | **Hemodynamic impact** | Minimal | Moderate to significant | Severe | | **Treatment** | Controversial; may observe if low risk | Anticoagulate | Anticoagulate ± thrombolysis | | **Mortality if untreated** | ~2% | ~5–10% | ~30% | **High-Yield:** Segmental PE carries clinically significant mortality risk and mandates anticoagulation. The absence of RV dilatation does NOT downgrade the clinical significance of a segmental clot—it simply indicates hemodynamic stability at the moment of imaging. ### Why This Is Segmental PE 1. Filling defect is in a named segmental artery (right lower lobe segmental branch) 2. Size and location place it above subsegmental threshold 3. Acute presentation with compatible symptoms and risk factors 4. No evidence of chronic changes (organized thrombus, bronchial collaterals) **Clinical Pearl:** RV dilatation is a marker of acute RV strain and hemodynamic compromise, but its *absence* does not exclude significant PE. A segmental PE can be hemodynamically stable yet still require anticoagulation to prevent propagation and recurrence. **Mnemonic: CTPA Severity Tiers** — **S**ubsegmental (Small, Stable, Sometimes observe), **S**egmental (Significant, Start anticoagulation), **L**obar (Large, Life-threatening, Consider thrombolysis).