In primary tuberculosis, which lymph node group is most commonly involved as part of the Ghon complex?

Explanation

## The Ghon Complex in Primary Tuberculosis **Key Point:** The Ghon complex is the characteristic lesion of primary tuberculosis, consisting of three components that develop in a specific anatomical pattern. ### Components of the Ghon Complex The Ghon complex comprises three essential elements: 1. **Ghon focus (subpleural focus)** — the initial parenchymal lesion, typically in the **lower lobes** (more commonly right), at the lung periphery 2. **Lymphangitis** — inflammation of lymphatic vessels draining the Ghon focus 3. **Regional lymphadenitis** — enlargement of **hilar and mediastinal lymph nodes** (the most commonly involved nodes) **High-Yield:** The **hilar and mediastinal lymph nodes** are the most characteristic and consistently involved nodes in primary TB. This is the hallmark of primary TB, distinguishing it from secondary TB (which typically involves apical and posterior segments without significant lymphadenopathy). ### Anatomical Pattern ```mermaid flowchart TD A[Inhalation of tubercle bacilli]:::action --> B[Lodgment in lung periphery]:::action B --> C[Ghon focus - subpleural lesion]:::outcome C --> D[Lymphangitis along draining vessels]:::action D --> E[Hilar and mediastinal lymph node enlargement]:::outcome E --> F[Ghon complex formed]:::outcome F --> G{Immune response adequate?}:::decision G -->|Yes| H[Healing with fibrosis and calcification]:::action G -->|No| I[Progressive primary TB]:::urgent ``` **Clinical Pearl:** In primary TB, **lymph node involvement is more prominent than parenchymal disease**, whereas in secondary TB, **parenchymal cavitary disease dominates with minimal lymphadenopathy**. This is a key distinguishing feature on imaging. ### Comparison: Primary vs. Secondary TB | Feature | Primary TB | Secondary TB | | --- | --- | --- | | **Lymph node involvement** | **Prominent (hilar/mediastinal)** | Minimal | | **Parenchymal lesion** | Small Ghon focus | Large cavitary lesions | | **Location** | Lower lobes (periphery) | Apical and posterior segments | | **Cavitation** | Rare | Common | | **Age group** | Children, immunocompromised | Adults, reactivation | **Mnemonic:** **HIM** — Hilar nodes, Involvement (lymphatic), Mediastinal nodes (in primary TB)