A 58-year-old woman presents to the emergency department with acute onset dyspnea and right-sided pleuritic chest pain. She returned from a 12-hour flight 3 days ago. Vital signs: BP 128/82 mmHg, HR 108/min, RR 22/min, SpO₂ 94% on room air. D-dimer is elevated at 2.8 μg/mL. CT pulmonary angiography (CTPA) is performed. Which of the following findings on CTPA would be most specific for acute pulmonary embolism?

Explanation

## CT Pulmonary Angiography (CTPA) Findings in PE **Key Point:** The most specific CT finding for acute pulmonary embolism is a **filling defect (thrombus) within the pulmonary artery lumen that is surrounded by contrast material** — the "contrast-surrounded" or "central" sign. ### Direct Signs of PE on CTPA | Finding | Specificity | Description | |---------|-------------|-------------| | **Central filling defect** | Very high | Thrombus within artery lumen, contrast on all sides | | **Peripheral wedge-shaped opacity** | Low | Infarction (Hampton's hump) — occurs in only 10% of PEs | | **Arterial cut-off sign** | High | Abrupt termination of artery | | **Saddle embolus** | High | Thrombus straddling pulmonary artery bifurcation | **High-Yield:** A filling defect that is **eccentrically located** (touching the vessel wall) or **not completely surrounded by contrast** may represent motion artifact or beam hardening and is less specific. The **central filling defect** (completely surrounded by contrast) is the gold standard sign. ### Why Other Options Are Incorrect - **Wedge-shaped peripheral opacity (Hampton's hump):** This is a sign of **pulmonary infarction**, which occurs in only 10% of PE cases. It is a secondary/indirect sign and is NOT specific to PE — it can occur with other causes of infarction. - **Cardiomegaly with dilated right atrium:** This is a sign of **right heart strain** secondary to PE, not a direct sign of thromboembolism itself. It is indirect and nonspecific. - **Atelectasis:** This is a nonspecific finding that can occur with many pulmonary conditions and is not diagnostic of PE. **Clinical Pearl:** Subsegmental PE (filling defects in subsegmental arteries only) has lower clinical significance than lobar or segmental PE. In a hemodynamically stable patient with subsegmental PE and no prior DVT/PE, anticoagulation may be deferred if clinical probability is low. **Mnemonic — CTPA Signs of PE:** **"CFAS"** - **C**entral filling defect (most specific) - **F**ilament sign (thin thrombus) - **A**rterial cut-off - **S**addle embolus (at bifurcation) [cite:Harrison 21e Ch 297]