The "Tree-in-Bud" Pattern

This pattern signifies the endobronchial spread of disease, typically reflecting bronchiolar impaction with mucus, pus, or fluid. Appearance: Centrilobular branching linear structures with nodular tips (resembling a budding twig). Key Differentials: 1. Infection: Mycobacteria (TB, MAC), bacterial bronchopneumonia, viral, or fungal. 2. Aspiration: Recurrent/chronic aspiration. 3. Airway Disease: Cystic Fibrosis or allergic bronchopulmonary aspergillosis (ABPA). Takeaway: It almost ALWAYS indicates an active inflammatory or infectious process, rarely malignancy.