tree in bud sign
Definition A CT appearance that loosely mimics the branching pattern of a budding tree. The tree in bud pattern refers to small centrilobular opacities/nodules and concomitant branching opacities that correspond to luminal impaction of bronchioles focally dilated with mucus, pus, or fluid, and accompanied by bronchial wall thickening and peribronchiolar inflammation, which highlight the normally invisible branching course of the peripheral airways.
The nodules and connecting branches are peripheral but spare the subpleural lung (bottom is the CT image).
Differential diagnosis Whilst it was first described in tuberculosis, the tree in bud pattern is nonspecific; it can be idiopathic or linked to immune disorders, congenital conditions, aspiration, neoplasia and, where small airways are involved, infections by any bug, including viruses, parasites, fungi, bacteria, and mycobacteria, in which the analogous “buds” of the tree-in-bud pattern correspond to globs of caseous material in respiratory bronchioles and alveolar ducts, while the branches correspond to goo in thickened terminal bronchioles. “Softer” centrilobular nodules of ground-glass attenuation occur in patients with subacute hypersensitivity pneumonitis, metastatic calcification, Churg-Strauss syndrome, microscopic polyangiitis, systemic lupus erythematosus, and respiratory bronchiolitis-associated interstitial lung disease.
Synonym Tree in bud appearance References emedicine.medscape.com/article/353200-overview
Journal of Thoracic Imaging:March 2012 – Volume 27 – Issue 2 – p W27