Jannette Collins ; Donna Blankenbaker ; Eric J. Stern
Bronchiolitis and bronchiolectasis are nonspecific inflammatory processes of the small airways caused by many different conditions. Imaging of bronchiolar disease is best performed by CT scanning, especially thin-section CT scanning. One characteristic of bronchiolar disease is a tree-in-bud pattern on CT, first used as a descriptor by Im et al.  to describe the appearance of the endobronchial spread of Mvcobacterium tuberculosis. This pattern can also be described as resembling childhood toy “jacks”. The tree-in-bud pattern has become a popular descriptive term for many bronchiolar disease processes with similar appearances , and it is often used inappropriately to imply a pathognomonic finding for tuberculosis. In this pictorial essay, we review bronchiolar anatomy and the CT appearance of bronchiolar diseases emphasizing those disorders likely to produce the tree-in-bud pattern and pitfalls in the diagnosis of bronchiolar disease using CT findings.