Tree-in-bud sign or pattern describes the CT appearance of multiple areas of centrilobular nodules with a linear branching pattern. Although initially described in patients with endobronchial tuberculosis, it is now recognized in a large number of conditions.
While the tree-in-bud appearance usually represents endobronchial spread of infection, given the closeness of small pulmonary arteries and small airways (sharing branching morphology-bronchovascular bundle), a rarer cause of the tree-in-bud sign is infiltration of the small pulmonary arteries or axial interstitium.
- infective bronchiolitis
- bacterial pneumonia, e.g. Staphylococcus aureus, Haemophilus influenzae, Mycobacterium tuberculosis, Mycobacterium avium (MAIC)
- viral pneumonia
- fungal pneumonia, e.g. aspergillus
- allergic bronchopulmonary aspergillosis (ABPA)
- pneumocystis pneumonia
- congenital
- cystic fibrosis
- immotile cilia syndrome, e.g. Kartagener syndrome
- yellow nail syndrome
- connective tissue disorders
- rheumatoid arthritis (RA)
- Sjögren syndrome
- bronchial
- obliterative (constrictive) bronchiolitis
- diffuse panbronchiolitis
- follicular bronchiolitis
- neoplastic (i.e. carcinomatous endarteritis or bronchovascular interstitial infiltration)
- bronchioloalveolar cell carcinoma
- distant metastatic disease (e.g. breast, liver, ovary, prostate, kidney)
- primary pulmonary lymphoma
- chronic lymphocytic leukemia
Information from Radiopaedia.org
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