A 58-year-old man with known diabetes presents with productive cough and fever. High-resolution CT chest shows a nodular opacity in the right upper lobe with surrounding ground-glass opacities and a tree-in-bud pattern. Which radiological finding best distinguishes endobronchial tuberculosis from bronchogenic carcinoma?

Explanation

## Endobronchial TB vs Bronchogenic Carcinoma: Radiological Discrimination **Key Point:** Endobronchial TB causes **segmental/lobar collapse with disproportionately small endobronchial lesion**, whereas bronchogenic carcinoma produces a **large mass with significant mass effect and mediastinal involvement**. ### Endobronchial Tuberculosis - Arises from erosion of a caseous lymph node into an adjacent bronchus - Endobronchial lesion is typically **small** (often <1 cm on imaging) - Causes **segmental or lobar atelectasis** (collapse) that is **disproportionate** to the size of the visible lesion - Minimal mass effect on surrounding structures - Hilar lymphadenopathy is common - Tree-in-bud pattern reflects distal bronchiolar involvement - Cavitation may occur but is not the primary finding ### Bronchogenic Carcinoma - Arises from malignant transformation of bronchial epithelium - Presents as a **large, irregular mass** with significant mass effect - Causes atelectasis **proportionate** to the size of the lesion - Often associated with pleural involvement, mediastinal widening, and distant metastases - Irregular, spiculated margins are typical - Necrotic hilar nodes are common but the primary lesion dominates imaging **High-Yield:** **Small endobronchial lesion + disproportionate lobar collapse** = **Endobronchial TB**. **Large mass + proportionate collapse** = **Bronchogenic carcinoma**. ### Comparison Table | Feature | Endobronchial TB | Bronchogenic Carcinoma | | --- | --- | --- | | **Primary lesion size** | Small (<1 cm) | Large (>3 cm) | | **Atelectasis** | Disproportionate to lesion | Proportionate to lesion | | **Mass effect** | Minimal | Significant | | **Margins** | May be irregular | Irregular, spiculated | | **Hilar nodes** | Present, may be necrotic | Present, necrotic | | **Pleural involvement** | Rare | Common | | **Associated findings** | Tree-in-bud, GGO | Pleural effusion, mediastinal shift | **Clinical Pearl:** The **mismatch between lesion size and degree of collapse** is the diagnostic clue: a tiny endobronchial lesion causing an entire lobe to collapse is classic TB; a large mass causing proportionate collapse is classic malignancy. **Mnemonic:** **SMALL lesion + BIG collapse** = **TB**. **BIG lesion + proportionate collapse** = **Cancer**. **Warning:** Both conditions can present with hilar lymphadenopathy and irregular margins. Do not rely on these features alone. The **size mismatch** between the endobronchial lesion and the degree of atelectasis is the most reliable discriminator.