From the Guidelines
A "tree-in-bud" appearance on Computed Tomography (CT) of the thorax is a significant radiological finding that indicates an active inflammatory or infectious process affecting the small airways, often associated with conditions such as infectious bronchiolitis, aspiration, viral infections, and cystic fibrosis. This pattern is characterized by small nodular opacities at the ends of bronchioles with branching linear opacities, resembling a budding tree. The most common causes of this finding include infectious bronchiolitis (particularly tuberculosis, non-tuberculous mycobacterial infections, and bacterial pneumonia) 1, as well as non-infectious conditions like bronchiolitis obliterans, diffuse panbronchiolitis, and allergic bronchopulmonary aspergillosis.
When identified on a CT scan, this finding typically warrants further clinical correlation and potentially additional diagnostic testing to determine the specific etiology. The distribution of the tree-in-bud pattern can provide clues to the underlying cause, such as upper lobe predominance suggesting tuberculosis, while diffuse distribution could indicate viral infection or aspiration 1. It is essential to consider the clinical context and perform a comprehensive evaluation, including medical history, physical examination, physiologic studies, and radiographic studies, to determine the underlying cause of the tree-in-bud pattern.
Some key points to consider when evaluating a tree-in-bud pattern on CT thorax include:
- The pattern is often associated with infectious bronchiolitis, particularly non-tuberculous mycobacterial infections 1
- The distribution of the pattern can provide clues to the underlying cause, such as upper lobe predominance suggesting tuberculosis 1
- A comprehensive evaluation, including medical history, physical examination, physiologic studies, and radiographic studies, is essential to determine the underlying cause of the tree-in-bud pattern 1
- Further diagnostic testing, such as bronchoscopy with lavage or surgical lung biopsy, may be necessary to confirm the diagnosis in selected cases 1
From the Research
Significance of Tree-in-Bud Appearance
The tree-in-bud appearance on Computed Tomography (CT) of the thorax is a significant radiologic finding that can indicate various conditions affecting the small airways.
- This pattern is characterized by small centrilobular nodules of soft-tissue attenuation connected to multiple branching linear structures of similar caliber that originate from a single stalk 2.
- The tree-in-bud pattern can be seen in a range of diseases, including infections (bacterial, fungal, viral, or parasitic), congenital disorders, idiopathic disorders (obliterative bronchiolitis, panbronchiolitis), aspiration or inhalation of foreign substances, immunologic disorders, and connective tissue disorders 2, 3.
- It is also associated with peripheral pulmonary vascular diseases, such as neoplastic pulmonary emboli 2.
Radiologic and Microbiologic Correlation
The tree-in-bud pattern has been correlated with various microbiologic etiologies, including infectious and non-infectious causes.
- A study found that 67.5% of patients with the tree-in-bud pattern had an infectious etiology, while 10.4% had aspiration pneumonia 4.
- The relative incidence of various organisms isolated in patients with the tree-in-bud pattern reflected the overall incidence of these bacteria in community- or hospital-acquired populations 4.
- Another study found that the tree-in-bud pattern was present in 17.6% of cases with acute bronchitis or pneumonia and 25.6% of cases with bronchiectasis 3.
Diagnostic Utility
The tree-in-bud pattern can be a useful diagnostic tool in preventing diagnostic errors and suggesting the appropriate diagnosis.
- Knowledge of the many causes of this pattern can help in preventing diagnostic errors 2.
- The presence of additional radiologic findings, along with the history and clinical presentation, can often be useful in suggesting the appropriate diagnosis 2.
- High-resolution computed tomography (HRCT) can provide a good insight into small airways disease and allow for precise localization for biopsy procedures and exact follow-up after institution of therapy 5.
- Computer-assisted detection (CAD) systems have been developed to automatically detect tree-in-bud patterns, which can assist in clinical and research investigation of this pathology 6.