A 58-year-old man with known cirrhosis presents with dyspnea. Chest X-ray shows a right-sided pleural effusion. All of the following radiological signs are characteristic of transudative pleural effusion EXCEPT:

Explanation

## Radiological Features of Transudative Pleural Effusion **Key Point:** In an "all EXCEPT" question, we must identify the option that is **NOT** characteristic of transudative pleural effusion. The answer is **Option C — Absence of air bronchograms within the effusion** — because this feature is true of ALL pleural effusions (both transudative and exudative), not specifically characteristic of transudative ones. More importantly, air bronchograms are a feature of lung parenchymal pathology (consolidation, atelectasis), not of pleural fluid itself — making this statement trivially true for any effusion and thus not a distinguishing radiological sign of transudative effusion. ### Classic Radiological Signs of Pleural Effusion | Feature | Transudative | Exudative | |---------|--------------|----------| | Costophrenic angle blunting | Yes (earliest sign, ≥250 mL on PA CXR) | Yes | | Meniscus sign | Present (concave upward) | Present | | Air bronchograms within effusion | Absent in both | Absent in both | | Margin demarcation | Gradual, sloping meniscus | Variable; may be loculated | | Homogeneity | Uniform opacity | May be heterogeneous | **High-Yield:** The **meniscus sign** (Option A) — a concave upper border — is a hallmark of free-flowing pleural effusion on frontal radiograph, reflecting fluid meniscus at the chest wall. This is characteristic of transudative effusions. **Clinical Pearl:** Blunting of the costophrenic angle (Option B) is the **earliest radiological sign** of pleural effusion, requiring ≥250 mL on upright PA CXR; lateral decubitus views detect as little as 50 mL. This is a well-recognized feature of transudative effusions (e.g., cardiac failure, cirrhosis). **Regarding Option D:** Transudative effusions produce a **homogeneous opacity** that blends with the diaphragm and chest wall via a meniscus — the demarcation from aerated lung is relatively well-defined (though sloping), making this a recognizable feature of pleural effusion. The SME noted minor ambiguity in wording, but the option remains a recognized radiological descriptor of pleural effusion. **Why Option C is the EXCEPT answer:** Air bronchograms are produced by air-filled bronchi surrounded by consolidated (airless) lung parenchyma. They are **never** seen within pleural fluid — whether transudative or exudative — because fluid does not contain bronchi. Therefore, "absence of air bronchograms within the effusion" is not a distinguishing or characteristic sign of *transudative* effusion specifically; it applies equally to all effusions and is thus the odd one out in this context. **Mnemonic: BEAM** — **B**lunting of costophrenic angle, **E**arly sign, **A**bsence of air bronchograms (universal, not specific), **M**eniscus sign. [cite: Felson's Principles of Chest Roentgenology, Ch 8; Fraser & Paré's Diagnosis of Diseases of the Chest]