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The tree-in-bud pattern represents bronchiolar luminal impaction with mucus, pus or fluid, which demarcates the normally invisible branching course of the distal peripheral pathways, thus resembling a tree branch studded… Click to show full abstract
The tree-in-bud pattern represents bronchiolar luminal impaction with mucus, pus or fluid, which demarcates the normally invisible branching course of the distal peripheral pathways, thus resembling a tree branch studded with buds on High-Resolution CT of the lungs (Figs. 1, 2) [1]. This sign corresponds to small (2–4 mm) and peripheral (close to the pleural surface) well-defined small nodules of soft-tissue attenuation which are connected to linear branching opacities with more than one contiguous branching site [1]. It is a pattern of centrolobular nodules characterized by impaction of the terminal bronchioles. Initially, the tree-in-bud sign had been described by Im as indicating endobronchial spread of Mycobacterium tuberculosis [2], but it is now known that the pattern can occur in various peripheral airway diseases such as infection (bacterial, fungal, viral or parasitic), congenital or idiopathic disorders (obliterative bronchiolitis, panbronchiolitis), inhalation of foreign substances, immunologic tissue disorders, and peripheral pulmonary vascular diseases (neoplastic pulmonary emboli) [1, 3, 4]. Because the lung bases are visible in nearly all abdomen CT studies, recognition of this sign is important for abdominal imagers.