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Tree-in-bud

Mohamed Attaya MD^a, Eman Attaya MD^b,Ebtesam Islam MD PhD^c

Correspondence to Ebtesam Islam MD PhD
Email: ebtesam.islam@ttuhsc.edu

SWRCCC 2014;2.(8):42-43
doi:10.12746/swrccc2014.0208.104

Figure 1 CT scan with tree-in-bud pattern

Figure 2 Drawing rendition of tree-in-bud

General

Bronchioles refer to the terminal passageways for gas exchange in the lungs. They are not normally seen on computed tomography scans due to their small size (less than or equal to 1 mm). However, in the presence of disease processes which involve the bronchioles (i.e., infectious or inflammatory conditions), they can easily be identified. Among the many patterns used to describe diseased bronchioles, the most recognized is the tree-in-bud pattern. It was initially used by JG Im to describe the endobronchial spread of Mycobacterium tuberculosis.¹ However, since its first use in 1993 the tree-in-bud pattern has been associated with multiple etiologies.

Histopathology
The tree-in-bud pattern seen on CT represents radiologic sequelae of an infectious or inflammatory process. Generally, these often result in bronchial wall thickening with replacement of the normally air-filled lumen with mucous or pus. As a result, involved bronchioles are more conspicuous on computed tomography imaging. The tree-in-bud pattern has been likened to finger-in-glove appearance and children’s toy jacks. Figure 1 is a CT scan of a patient with tree-in-bud pattern, with a representation circled. Figure 2 is a drawing rendition of tree-in-bud.

Differential Diagnosis

The differential diagnosis for the tree-in-bud pattern is extensive and includes infections, congenital conditions, neoplasms, and idiopathic causes (Table).

Table: Differential diagnoses of tree-in-bud

Respiratory infections cause about 72% of cases with 39% due to Mycobacterial cases, 27% due to other bacteria, and 3% due to viruses. Mycobacterium avium complex is the most common cause in most series.² However, the classic cause of tree-in-bud is Mycobacterium tuberculosis, especially when it is active and contagious and associated with cavitary lesions.³ Aspiration is also a common cause of the tree-in-bud formation.¹ It is important for clinicians to remember that this pattern has an extensive differential when evaluating patients. 

References

1. Im JG, Itoh H, Shim YS, Lee JH, Ahn J, Han MC, Noma S. Pulmonary tuberculosis: CT findings--early active disease and sequential change with antituberculous therapy. Radiology 1993;186(3):653-60.
2. Miller Jr W T, Panosian J S. Causes and Imaging Patterns of Tree-in-Bud Opacities. CHEST 2013; 144(6):1883–1892
3. Gosset N, Bankier A, and Eisenberg R. Tree-In-Bud Pattern. Am J Roentgen 2009; 193: W472-W477.

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