From the Guidelines
Tree-in-bud pattern is a radiological finding that signifies infectious bronchiolitis or bronchiectasis, often associated with mycobacterial infections, such as Mycobacterium avium complex (MAC) 1. This pattern is characterized by centrilobular nodules connected by linear opacities, resembling the branches of a tree. The presence of a tree-in-bud pattern on imaging is a significant finding, as it can indicate underlying bronchiolar disease, which may require specific diagnosis and treatment 1.
Some key points to consider:
- The tree-in-bud pattern is often seen in patients with MAC lung disease, particularly in the nodular bronchiectatic form of the disease 1.
- This pattern can also be associated with other infectious agents, such as respiratory syncytial virus (RSV) or Mycoplasma pneumoniae 1.
- Treatment for tree-in-bud pattern typically involves antimicrobial therapy, such as macrolides, ethambutol, and rifamycins, for MAC infections 1, or supportive care with bronchodilators and antipyretics for other infectious causes.
- Radiological outcomes can be used to evaluate the effectiveness of treatment, with improvements in chest X-ray and CT scores correlating with culture conversion and clinical response 1.
In clinical practice, the presence of a tree-in-bud pattern on imaging should prompt a thorough evaluation, including comprehensive medical history, physical examination, physiologic testing, and radiographic studies 1, to determine the underlying cause and guide treatment.
From the Research
Significance of Tree-in-Bud Pattern
The tree-in-bud pattern is a significant finding on imaging, particularly on high-resolution computed tomography (CT) scans of the lungs. 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.
Causes of Tree-in-Bud Pattern
The tree-in-bud pattern can be caused by a variety of entities, including:
- Infections (bacterial, fungal, viral, or parasitic) 2, 3, 4
- Congenital disorders 2
- Idiopathic disorders (obliterative bronchiolitis, panbronchiolitis) 2
- Aspiration or inhalation of foreign substances 2, 3, 4
- Immunologic disorders 2
- Connective tissue disorders 2
- Peripheral pulmonary vascular diseases (neoplastic pulmonary emboli) 2
Diagnostic Approach
A detailed clinical history and evaluation of additional radiologic findings can help suggest the appropriate diagnosis 2, 5. High-resolution CT (HRCT) scanning of the chest is a valuable diagnostic tool in guiding diagnosis, as different subtypes of bronchiolar disorders may present with characteristic image findings 5.
Radiologic and Microbiologic Correlation
The tree-in-bud pattern reflects endobronchiolar inflammation, mainly due to infectious causes, but also due to non-infectious causes 3. The microbiologic etiology in patients with this finding is similar to that of the general population (community-acquired versus hospital-acquired) 3. Patterns of disease associated with tree-in-bud opacities can provide clues to the most likely diagnosis, such as:
- Alternating areas of normal lung with regions of small airways disease (random small airways pattern) specific for Mycobacterium avium complex infection 4
- Nearly uniform distribution of bronchiectasis (widespread bronchiectasis pattern) specific for diseases predisposing to airway infection 4
- Consolidation and tree-in-bud opacities (bronchopneumonia pattern) usually due to bacterial infection or aspiration 4
- Dependent distribution and esophageal abnormality with tree-in-bud opacities associated with aspiration 4