## Radiological Features of Pulmonary Tuberculosis ### Classic TB Findings on Chest X-ray **Key Point:** Pulmonary TB typically presents with upper lobe cavitary disease, but the pattern of pleural involvement differs from other consolidative processes. | Feature | Typical in TB | Explanation | |---------|---------------|-------------| | Air bronchogram | Yes | Indicates patent airways within consolidation; common in TB | | Traction bronchiectasis | Yes | Occurs at margins of fibrotic lesions as lung retracts | | Pleural effusion | Yes | Can occur, but shift is TOWARD affected side (not away) | | Calcified hilar nodes | Yes | Hallmark of healed/chronic TB; "eggshell" calcification classic | | Cavitation | Yes | Occurs in 40–50% of pulmonary TB cases | ### Why Mediastinal Shift Away is Wrong **High-Yield:** When pleural effusion accompanies TB consolidation in the upper lobe, any mediastinal shift would be **toward** the affected side (due to the mass effect of consolidation), not away. A shift **away** from the affected side suggests either: - Tension pneumothorax (emergency) - Massive pleural effusion with atelectasis (usually non-TB causes like malignancy, heart failure) - Contralateral lung collapse **Clinical Pearl:** TB-associated pleural effusion is typically exudative and lymphocytic, but it does not cause the degree of mass effect that would push the mediastinum away from the lesion. ### Correct Associations 1. **Air bronchogram** — patent bronchi visible within opacified lung; seen in TB consolidation 2. **Traction bronchiectasis** — bronchial dilatation at the edge of fibrotic cavitary lesions 3. **Calcified hilar nodes** — eggshell or dense calcification; pathognomonic for healed TB **Mnemonic: CATCH-TB** — Cavitation, Air bronchogram, Traction bronchiectasis, Calcification, Hilar involvement, TB upper lobe [cite:Felson's Principles of Chest Roentgenology Ch 8]
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