Which radiological feature best distinguishes primary pulmonary tuberculosis from reactivation tuberculosis on chest X-ray?

Explanation

## Distinguishing Primary vs Reactivation TB on CXR **Key Point:** Hilar lymphadenopathy is the hallmark of primary TB, whereas cavitary disease in the apical-posterior upper lobes is characteristic of reactivation TB. ### Primary Tuberculosis Findings - Hilar and mediastinal lymphadenopathy (often unilateral) - Parenchymal consolidation (usually lower and middle lobes) - Atelectasis due to bronchial compression by enlarged nodes - Minimal or no cavitation - Occurs within 6 months of infection ### Reactivation Tuberculosis Findings - Cavitary lesions in apical-posterior segments of upper lobes - Upper lobe predominance (gravity-dependent, high oxygen tension) - Minimal lymphadenopathy - Bronchial wall thickening and endobronchial spread - Occurs months to years after initial infection ### Comparison Table | Feature | Primary TB | Reactivation TB | |---------|-----------|----------------| | **Lymphadenopathy** | Prominent (hilar/mediastinal) | Minimal or absent | | **Cavitation** | Rare | Common (apical-posterior) | | **Lobe involvement** | Lower/middle lobes | Upper lobes | | **Endobronchial spread** | Uncommon | Common | | **Miliary pattern** | Can occur | Less common | | **Timeline** | Early (< 6 months) | Late (months–years) | **Clinical Pearl:** A child with TB presenting with hilar lymphadenopathy + right middle lobe atelectasis = primary TB until proven otherwise. An adult with cavitary upper lobe disease = reactivation TB. **High-Yield:** In NEET PG, the question "primary vs reactivation" almost always hinges on lymphadenopathy (primary) vs cavitation (reactivation).