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This 71 year-old female presented with dyspnoea, pleuritic chest pain, hypoxia. She had a recent diagnosis of lower limb deep venous thrombosis, and a CT pulmonary angiogram was performed to investigate for possible pulmonary embolus. The patient had a background history of chronic airflow limitation, asthma and hypertension.

The image from the CTPA shows tree-in-bud centrilobular nodular opacities in the left lower lobe and right middle and lower lobes. Other findings (not shown) included moderate cylindrical brochiectasis of the right middle and lower lobes, and the left lower lobe. There was peripheral patchy consolidation in RUL,RML,RLL, and LLL. There was mild right hilar and mediastinal lymphadenopathy, and a moderate hiatus hernia. There were no pleural effusions and no pulmonary emboli.

Tree-in-bud nodular pulmonary opacities imply dilatation and filling of distal bronchioles and may be seen in a variety of conditions. Originally described in active endobronchial tuberculosis, they have been described in other bacterial infections such as atypical Mycobacterial infections (Lady Windermere syndrome, middle lobe syndrome), Haemophilus influenzae, and Staphylococcus aureus. Viral (cytomegalovirus, respiratory syncytial virus) and fungal (Aspergillus spp.) infections may also show this pattern. Congenital causes of bronchiectasis such as cystic fibrosis and Kartagener’s syndrome may show it. Other causes include: obliterative bronchiolitis; Asian panbronchiolitis; aspiration or toxic inhalation; allergic bronchopulmonary aspergillosis; connective tissue diseases such as Sjogren’s syndrome and rheumatoid arthritis; and pulmonary tumour emboli.

Reference: Rossi SA et al. Tree-in-Bud Pattern at Thin-Section CT of the Lungs: Radiologic-Pathologic Overview. Radiographics 2005;25:789-801.

Credit: Dr Laughlin Dawes