From the Guidelines
The presence of a tree-in-bud pattern in a lung nodule at the lung base is highly suggestive of an infectious or inflammatory process, particularly non-tuberculous mycobacterial (NTM) infections, and warrants further evaluation with sputum cultures, bronchoscopy, or lung biopsy to guide targeted therapy. This radiological finding is characterized by a pattern resembling a budding tree on CT scans, indicating bronchiolar inflammation with mucus plugging or infectious material filling the terminal bronchioles 1. The tree-in-bud pattern is a key feature of NTM lung disease, particularly in the nodular bronchiectatic form, which tends to have a slower progression than cavitary disease but can still lead to significant morbidity and mortality if left untreated 1.
The location of the tree-in-bud pattern at the lung base may suggest aspiration-related pathology or gravity-dependent infection, as infectious material can settle in dependent lung regions. Common causes of this pattern include bacterial infections, fungal infections, viral pneumonias, and aspiration, as well as non-infectious conditions like bronchiolitis, cystic fibrosis, or allergic bronchopulmonary aspergillosis 1.
Given the potential for significant morbidity and mortality associated with NTM lung disease, it is essential to prioritize further evaluation and targeted therapy to improve patient outcomes. The use of high-resolution CT (HRCT) scans with expiratory cuts can help identify the tree-in-bud pattern and other features of bronchiolar disease, such as air-trapping and mosaic attenuation, which can inform the diagnosis and management of NTM lung disease 1.
In terms of management, treatment depends on the underlying etiology, typically involving targeted antimicrobial therapy for infections or anti-inflammatory medications for non-infectious causes. For NTM lung disease, therapy directed at the specific mycobacterial pathogen, such as MAC, can lead to sputum conversion or radiographic improvement 1. However, the management of NTM lung disease can be complex, and strategies aimed at bronchiectasis per se, such as airway clearance, may also be necessary to improve patient symptoms.
From the Research
Significance of Tree-in-Bud Pattern in Lung Nodule at Lung Base
- The tree-in-bud pattern is a radiologic finding that can be seen on computed tomography (CT) scans of the lungs, characterized by small centrilobular nodules connected to branching linear structures 2.
- This pattern is associated with various conditions, including infections, congenital disorders, idiopathic disorders, aspiration or inhalation of foreign substances, immunologic disorders, and connective tissue disorders 2, 3.
- The tree-in-bud pattern can be seen in patients with pulmonary infections, such as bronchitis or pneumonia, and is also associated with bronchiectasis 3, 4.
- In the context of central lung cancer, the tree-in-bud pattern is commonly detected and is associated with obstructive bronchial mucoid impaction distal to the cancer 5.
- The pattern is characterized by bronchiolectasis, bronchiolar lumen filled by mucus and inflammatory exudates, and wall thickening with inflammatory cells infiltration 5.
Clinical Correlation
- The tree-in-bud pattern can be seen in patients with various clinical presentations, including respiratory symptoms such as cough and dyspnea 4.
- The pattern is not specific to any particular condition and can be seen in patients with infectious and non-infectious etiologies 4.
- In cats, the tree-in-bud pattern has been described as a characteristic of bronchial or bronchiolar plugging and bronchial disease 6.
Radiologic Findings
- The tree-in-bud pattern is typically seen on high-resolution CT scans of the lungs and is characterized by small centrilobular nodules connected to branching linear structures 2, 3.
- The pattern can be associated with other radiologic findings, such as consolidation and ground-glass opacities 5.
- On radiographs, the tree-in-bud pattern can appear as soft-tissue opacity nodules, which can be underestimated compared to CT scans 6.