The contrast-enhanced CT chest images shown above demonstrate which of the following conditions?

Explanation

## Image Findings * **Coronal and axial contrast-enhanced CT images** of the chest are provided. * In both views, there are prominent **intraluminal filling defects** within the contrast-opacified pulmonary arteries. * A large, central low-attenuation filling defect is seen straddling the **main pulmonary artery bifurcation**, extending into both the right and left main pulmonary arteries. This is characteristic of a **saddle embolus**. * Further filling defects are visible in more peripheral segmental pulmonary artery branches. * The **axial view** clearly shows the 'polo mint' sign, where a central low-attenuation thrombus is surrounded by contrast material within the pulmonary artery lumen. ## Diagnosis **Key Point:** The presence of **intraluminal filling defects** within contrast-opacified pulmonary arteries, as seen in these images, is the pathognomonic finding for **acute pulmonary embolism (PE)**. The images demonstrate multiple acute pulmonary emboli, including a large saddle embolus, which is a critical finding indicating significant obstruction of pulmonary blood flow. This condition is life-threatening and requires urgent management. ## Differential Diagnosis | Feature | Acute Pulmonary Embolism | Aortic Dissection | Severe Pulmonary Hypertension | Mediastinal Lymphadenopathy | | :------------------ | :----------------------------------------------------- | :---------------------------------------------------- | :-------------------------------------------------------- | :-------------------------------------------------------- | | **Key CT Finding** | Intraluminal filling defects in pulmonary arteries | Intimal flap separating true/false lumens in aorta | Dilated main pulmonary artery, RV hypertrophy | Enlarged mediastinal lymph nodes (>10mm short axis) | | **Image Correlation** | Clearly visible filling defects (saddle embolus, etc.) | No intimal flap or double lumen in aorta | Main pulmonary artery not disproportionately dilated; primary finding is embolus | No prominent enlarged lymph nodes as primary pathology | ## Clinical Relevance **Clinical Pearl:** Acute pulmonary embolism is a medical emergency with high mortality if untreated. Early diagnosis via CT Pulmonary Angiography (CTPA) is crucial for initiating appropriate anticoagulation or thrombolytic therapy. ## High-Yield for NEET PG **High-Yield:** CT Pulmonary Angiography (CTPA) is the **gold standard** imaging modality for diagnosing acute pulmonary embolism due to its high sensitivity and specificity. **Key Point:** A **saddle embolus** involves the main pulmonary artery bifurcation and is associated with a higher risk of hemodynamic instability and adverse outcomes. ## Common Traps **Warning:** Differentiating acute from chronic PE on CT can be challenging. Acute emboli typically appear as central, low-attenuation filling defects, often forming acute angles with the vessel wall. Chronic emboli may appear as eccentric, calcified, or web-like lesions, often forming obtuse angles with the vessel wall. ## Reference [cite:Grainger & Allison's Diagnostic Radiology Ch 19]