From the Guidelines
Tree-in-bud appearance on high-resolution computed tomography (HRCT) is a radiological pattern that indicates inflammation or infection in the small airways, and is most commonly associated with infectious bronchiolitis, particularly from mycobacterial infections like tuberculosis or nontuberculous mycobacterial infections, as seen in a study published in the American Journal of Respiratory and Critical Care Medicine 1. This pattern is characterized by small centrilobular nodules connected to linear branching opacities, resembling a budding tree. The tree-in-bud pattern can also be seen in other conditions such as bacterial pneumonia, fungal infections, viral bronchiolitis, bronchiectasis with mucoid impaction, aspiration, and some non-infectious conditions like cystic fibrosis or allergic bronchopulmonary aspergillosis. Some key points to consider when evaluating tree-in-bud appearance on HRCT include:
- The pattern develops because inflammatory exudates or mucus plugs fill and distend the bronchiolar lumen and surrounding alveolar spaces, creating the characteristic branching appearance on HRCT.
- Further diagnostic workup is typically needed, including sputum cultures, bronchoscopy with bronchoalveolar lavage, or sometimes lung biopsy to identify the specific cause, as suggested in a study published in Chest 1.
- Treatment depends on the underlying etiology, ranging from antibiotics for bacterial infections to antifungals for fungal causes, or management of underlying conditions like asthma or cystic fibrosis.
- The diagnosis of bronchiectasis, which can present with tree-in-bud appearance, depends on visualizing the typical changes either radiographically or anatomically, with HRCT scanning being the preferred method, as stated in a study published in Chest 1.
From the Research
Tree-in-Bud Appearance in HRCT
The tree-in-bud appearance in high-resolution computed tomography (HRCT) is a radiologic pattern that reflects bronchiolar mucoid impaction, occasionally with additional involvement of adjacent alveoli 2. This pattern can be caused by various factors, including:
- Infectious etiologies, such as Mycobacterium tuberculosis, nontuberculous mycobacteria, and other bacterial, fungal, or viral pathogens 2, 3
- Immunological, congenital, and idiopathic disorders 3
- Aspiration or inhalation of toxic agents 3
- Malignant conditions, such as chronic lymphatic leukemia 3
Radiological Features and Correlation with Clinical Outcome
The tree-in-bud pattern can be evaluated using various radiological scoring systems, such as the Brody and Bhalla scoring systems 4. These systems can be used to assess the severity of bronchiectasis and to monitor the response to treatment. Studies have shown that HRCT can be used as an objective measure of treatment response in bronchiectasis 4, 5, 6.
Correlation with Pulmonary Functional Tests
HRCT scores have been correlated with pulmonary functional tests, such as forced expiratory volume in one second (FEV1) 5. This correlation can be useful in evaluating the clinical impairment of patients with cystic fibrosis and other respiratory diseases.
Usefulness of HRCT in Macrolide Therapy
HRCT can be useful in predicting the treatment efficacy of macrolide therapy in patients with idiopathic bronchiectasis 6. The Bronchiectasis Radiologically Indexed CT Score (BRICS) can be used to classify patients with idiopathic bronchiectasis and to evaluate the response to macrolide therapy. Studies have shown that HRCT severity assessment can be useful in predicting treatment efficacy in patients with idiopathic bronchiectasis without previous acute exacerbations 6.