On HRCT chest, a 'tree-in-bud' pattern is observed in the right lower lobe. This pattern specifically indicates:

• A Perilymphatic micronodules around bronchovascular bundles
• B Centrilobular emphysema destroying the respiratory bronchioles
• C Lymphangitis carcinomatosa thickening interlobular septa
• D Endobronchial spread of infection filling the centrilobular bronchioles and alveolar ducts ✓

Explanation

Tree-in-bud pattern on HRCT represents dilatation and impaction of centrilobular bronchioles (the 'branches') and their terminal alveolar ducts/acini (the 'buds') with mucus, pus, or fluid. It is the hallmark of endobronchial spread of infection (TB, atypical mycobacteria, bacterial bronchopneumonia) or aspiration. Perilymphatic nodules characterize sarcoidosis. Centrilobular emphysema appears as low-attenuation areas without walls. Lymphangitis causes Kerley-B lines and interlobular septal thickening, not tree-in-bud.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.