Which of the following radiological signs is characteristic of pulmonary consolidation rather than atelectasis on a frontal chest X-ray?

Explanation

## Consolidation vs Collapse: Key Radiological Distinction **Key Point:** Air bronchograms are a hallmark of consolidation and indicate patent airways within consolidated lung parenchyma. They are absent in pure atelectasis because the airways themselves are collapsed. ### Characteristic Signs | Feature | Consolidation | Atelectasis (Collapse) | |---------|---|---| | **Air bronchogram** | **Present** ✓ | Absent | | **Silhouette sign** | May occur | May occur | | **Hilum displacement** | None or toward affected lobe | **Displaced toward affected lobe** | | **Mediastinal shift** | Away from affected side | **Toward affected side** | | **Volume** | Normal or increased | **Decreased** | **High-Yield:** Air bronchograms appear as dark (air-filled) branching lines within the white (opacified) consolidated lung. This sign is virtually pathognomonic for consolidation and helps differentiate it from other causes of opacity like pleural effusion or atelectasis. **Clinical Pearl:** In consolidation, the underlying lung architecture is preserved and airways remain patent, allowing air to be visible within the consolidated parenchyma. In atelectasis, the entire lobe loses volume and the airways collapse along with the parenchyma. ### Why Other Signs Are Less Specific - **Silhouette sign:** Occurs in both consolidation (when it involves the lung-mediastinal interface) and atelectasis (when the collapsed lobe abuts the heart or mediastinum). - **Hilum displacement:** Occurs in both, but direction differs (toward in collapse; variable in consolidation). - **Mediastinal shift:** Occurs in collapse (toward affected side due to volume loss); in consolidation, shift is away from the affected side or absent. [cite:Felson's Principles of Chest Roentgenology Ch 3]