Which of the following radiological findings is most characteristic of primary tuberculosis in children?

Explanation

## Primary Tuberculosis: Characteristic Imaging Features **Key Point:** Primary TB (usually in children and immunocompromised hosts) presents with **hilar and mediastinal lymphadenopathy** as the hallmark finding, often accompanied by segmental or lobar atelectasis. ### Radiological Pattern in Primary TB | Feature | Primary TB | Secondary TB | |---------|-----------|-------------| | **Typical location** | Hilar/mediastinal lymph nodes | Apical-posterior upper lobes | | **Cavitation** | Rare | Common (>50%) | | **Parenchymal consolidation** | Minimal or segmental | Extensive, often bilateral | | **Pleural involvement** | Can occur (effusion) | Less common | | **Age group** | Children, recent converters | Adults, reactivation | ### Why Hilar Lymphadenopathy? 1. **Ghon complex formation**: Primary infection occurs at the lung periphery (usually lower/middle lobes), with lymphatic spread to hilar nodes. 2. **Lymph node enlargement**: Nodes enlarge as the immune response develops, causing compression atelectasis of distal lung segments. 3. **Minimal cavitation**: The immune system in primary TB is still mounting a response; cavitary disease is rare unless dissemination occurs. **Clinical Pearl:** A child with hilar lymphadenopathy + segmental atelectasis ("atelectatic TB") + positive tuberculin skin test is primary TB until proven otherwise. **High-Yield:** The **Ghon focus** (peripheral consolidation) + **hilar lymphadenitis** + **lymphangitis** = Ghon complex — the pathognomonic triad of primary TB, though the hilar component dominates on CXR.