Tree-in-bud sign | Radiology Signs

Answer:

Centrilobular branching nodules due to impaction of bronchioles by mucus, pus, or fluid from endobronchial infection or aspiration, seen in conditions such as bacterial bronchopneumonia, mycobacterial infections (tuberculosis, nontuberculous mycobacteria), fungal infections, chronic aspiration pneumonia, cystic fibrosis, and less commonly autoimmune diseases or malignancy.

Why is it called so?

Named for its resemblance to the branching structures of a budding tree, with small centrilobular nodules representing buds and linear opacities depicting twigs or branches. The pattern was first described on thin-section CT by Im et al. in patients with endobronchial spread of pulmonary tuberculosis, and later characterized systematically by Collins et al. (AJR, 1998).

Pathophysiology

Develops from bronchiolar luminal impaction with mucus, pus, fluid, or inflammatory debris, accompanied by bronchiolar dilatation, wall thickening, and peribronchiolar inflammation, rendering normally invisible peripheral airways visible on high-resolution CT as centrilobular nodules 2-4 mm in diameter connected to branching linear structures.

Alternative names: Informally likened to the appearance of children’s toy “jacks”; the underlying CT pattern is also referred to as the tree-in-bud pattern.

Other associated named signs: Related to the broader category of centrilobular nodule/branching opacity patterns seen in small airways disease; contrasts with the random/miliary nodule distribution of hematogenous disease.

References

1. Collins J et al. CT patterns of bronchiolar disease: what is “tree-in-bud”? AJR Am J Roentgenol. 1998.
2. Rossi SE et al. Tree-in-bud pattern at thin-section CT of the lungs: radiologic-pathologic overview. Radiographics. 2005.