## Radiological Features of Pulmonary Tuberculosis ### Classic Findings in Active TB **Key Point:** The hallmark of pulmonary TB is cavitary disease in the upper lobes (apical and posterior segments), typically with surrounding consolidation and characteristic secondary signs. | Finding | Typical in TB | Mechanism | |---------|---------------|----------| | Air bronchogram | Yes | Consolidation with patent airways | | Traction bronchiectasis | Yes | Fibrosis pulling open airways at lesion margin | | Pleural effusion with shift AWAY from lesion | Yes | Restrictive fibrosis contracts lung | | Pleural effusion with shift TOWARD lesion | No | Indicates mass effect or tension — not typical TB | | Hilar lymph node calcification | Yes | Healed/inactive disease | ### Why Option 2 (Pleural Effusion with Mediastinal Shift TOWARD Affected Side) Is Wrong **High-Yield:** In pulmonary TB, the fibrotic process causes **volume loss** and **retraction** of the affected lung. This pulls the mediastinum **TOWARD** the lesion, not away from it. A shift **AWAY** from the affected side would indicate mass effect (as in malignancy or tension pneumothorax), which is not the mechanism in TB. **Clinical Pearl:** Pleural effusion in TB (usually exudative, lymphocyte-predominant) may occur, but the mediastinal shift pattern reflects the underlying pathology: TB causes fibrosis → volume loss → mediastinal shift toward the affected side. A shift away from the affected side would suggest a space-occupying lesion or tension effect — neither typical of TB. ### Other Correct Findings 1. **Air bronchogram** — consolidation with patent bronchi visible as lucent lines; common in TB consolidation. 2. **Traction bronchiectasis** — fibrosis at the margin pulls bronchi open; seen at the periphery of cavitary and fibrotic lesions. 4. **Hilar lymph node calcification** — "eggshell" or dense calcification in healed TB is pathognomonic.
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