CT chest shows a 'tree-in-bud' pattern (centrilobular nodules with branching linear opacities resembling a budding tree). This pattern specifically indicates:
- A Lymphangitic carcinomatosis
- B Endobronchial spread of infection — filling of bronchioles with secretions, pus, or mucus ✓
- C Centrilobular emphysema
- D Pulmonary arterial hypertension with pruning
Correct answer: B. Endobronchial spread of infection — filling of bronchioles with secretions, pus, or mucus
Explanation
The 'tree-in-bud' sign on HRCT represents filling of centrilobular bronchioles and their branches with secretions, pus, or mucus, creating a pattern that resembles tree branches covered with buds. It is the radiological correlate of endobronchial infection/inflammation, most classically seen in active tuberculosis (endobronchial spread), atypical mycobacterial infection (MAC), and bronchopneumonia. It is NOT seen in lymphangitic carcinomatosis (which causes interlobular septal thickening and beading) or emphysema.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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