## Distinguishing Collapse from Consolidation **Key Point:** The hallmark of collapse is loss of volume with secondary displacement of anatomical structures (fissures, mediastinum, diaphragm), whereas consolidation maintains normal or increased volume. ### Radiological Signs Comparison | Feature | Consolidation | Collapse | |---------|---|---| | **Volume** | Normal or increased | Decreased | | **Fissures** | Normal position | Displaced toward lesion | | **Air bronchogram** | Present (pathognomonic) | Absent or rare | | **Silhouette sign** | May occur | May occur | | **Mediastinal shift** | None | Toward affected side | | **Diaphragm** | Normal position | Elevated on affected side | **High-Yield:** Loss of volume with fissural displacement is the ONLY sign that definitively indicates collapse and excludes consolidation. Consolidation can mimic collapse in appearance, but volume loss is the discriminator. ### Why This Matters Clinically **Clinical Pearl:** Consolidation suggests infection, aspiration, or infarction (parenchymal process). Collapse suggests airway obstruction (tumor, mucus plug, foreign body) requiring different management. **Mnemonic — COLLAPSE signs:** - **C**ontraction (volume loss) - **O**bliteration of fissures (displacement) - **L**oss of normal landmarks - **L**ateral shift of mediastinum - **A**pex elevation (in upper lobe) - **P**osterior displacement of fissures - **S**ilhouette may occur - **E**levation of hemidiaphragm [cite:Felson's Principles of Chest Roentgenology] 
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