A 6-year-old child from rural India presents with persistent cough for 3 weeks, low-grade fever, and weight loss. Chest X-ray shows a hilar lymphadenopathy with a collapsed right middle lobe. Tuberculin skin test is positive. What is the most common site of tuberculosis in children?

Explanation

## Most Common Site of Pediatric TB **Key Point:** Pulmonary tuberculosis with hilar lymphadenopathy is the most common presentation of TB in children, accounting for 85–90% of all pediatric TB cases. ### Why Pulmonary TB Dominates in Children 1. **Primary complex formation** — When a child inhales *Mycobacterium tuberculosis*, the infection typically lodges in the lung parenchyma near the pleural surface, followed by lymphatic spread to hilar and mediastinal lymph nodes. 2. **Lymph node enlargement** — The hallmark of childhood TB is **hilar lymphadenopathy** (often with minimal or no parenchymal infiltrate), which may cause bronchial compression and atelectasis (as seen in this case with right middle lobe collapse). 3. **Low cavitation rate** — Unlike adults, children rarely develop cavitary disease due to their immature immune response and lower bacterial burden. ### Comparison of Pediatric TB Presentations | Presentation | Frequency | Key Features | Age Group | | --- | --- | --- | --- | | **Pulmonary TB (with hilar LAD)** | 85–90% | Cough, fever, weight loss; CXR shows hilar/mediastinal lymphadenopathy ± atelectasis | Any age | | **Miliary TB** | 1–3% | Hematogenous dissemination; "millet seed" appearance on CXR; high mortality | <5 years (early progressive) | | **TB meningitis** | 1–2% | Severe CNS disease; high morbidity/mortality; occurs weeks to months after primary infection | <5 years | | **Abdominal TB** | 1–2% | Lymphadenitis, ascites, hepatosplenomegaly; less common than pulmonary | Any age | **High-Yield:** The **primary complex** (lung infiltrate + hilar lymphadenopathy + lymphangitis) is the pathognomonic finding of childhood TB. Most children remain asymptomatic or have mild symptoms; the diagnosis is often made on screening or incidental CXR. **Clinical Pearl:** Hilar lymphadenopathy in a child with a positive tuberculin skin test and constitutional symptoms is TB until proven otherwise. Bronchial compression by enlarged nodes can cause lobar/segmental collapse (as in this case) and may mimic pneumonia. **Mnemonic — "CHAMP" for extrapulmonary TB sites (rare in children):** - **C**entral nervous system (meningitis) - **H**epatic/abdominal - **A**rticular/skeletal - **M**iliary - **P**leural [cite:Park 26e Ch 7]