Tree-in-bud pattern
Updates to Article Attributes
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 recognised in a large number of conditions.
Pathology
Pathogenesis
Simply put, the tree-in-bud pattern can be seen with two main sites of disease 3:
- distal airways
- distal pulmonary vasculature
More specifically, the pattern can be manifest because of the following disease processes, often in combination:
- airway-centered:
- bronchioles filled with pus or inflammatory exudate
- bronchiolitis: thickening of bronchiolar walls and bronchovascular bundle
-
bronchiectasis/bronchiolectasis with mucus plugging
- e.g. cystic fibrosis
- bronchovascular interstitial infiltration
- e.g. sarcoidosis, lymphoma, leukaemia 4,5
-
vascular-centered
-
tumour emboli to centrilobular arteries (or carcinomatous endarteritis)
- e.g. breast cancer, stomach cancer
- granulomatous response to excipient material in intravenous drug abusers 8,9
- e.g. intravenous talcosis or microcrystalline cellulose in crushed oral tablets (excipient lung disease)
-
tumour emboli to centrilobular arteries (or carcinomatous endarteritis)
Aetiology
While the tree-in-bud appearance usually represents an endobronchial spread of infection, given the proximity 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/arterioles or axial interstitium 3,6,7.
Causes include:
- infective bronchiolitis
- congenital
- connective tissue disorders
- bronchial
-
neoplastic (i.e. carcinomatous endarteritis 3,6,7or bronchovascular interstitial infiltration 4,5)
- bronchioloalveolar cell carcinoma
- distant metastatic disease (e.g. breast, liver, ovary, prostate, kidney)
- primary pulmonary lymphoma 5
- chronic lymphocytic leukemia 4
- periarterial granulomatous
Radiographic features
Tree-in-bud sign is not generally visible on plain radiographs 2. It is usually visible on standard CT, however, it is best seen on HRCT chest. Typically the centrilobular nodules are 2-4 mm in diameter and peripheral, within 5 mm of the pleural surface. The connection to opacified or thickened branching structures extends proximally (representing the dilated and opacified bronchioles or inflamed arterioles) 1-3,6.
Practical points
- using maximum intensity projection (MIP) can facilitate detection of particularly the centrilobular nodules 6
- identification of the tree-in-bud sign should urge you to
- look for further imaging findings e.g. thickening of the bronchial wall, narrowing of bronchi, bronchiectasis, consolidation, cavitation, necrotic lymphadenopathy
- determine the location (with gravitational or lower lobe predominance favouring aspiration) 6,7
- scrutinise patient history, including appropriate exposure history, as this may aid in determining the most likely diagnosis 6,7
-<li>bronchovascular interstitial infiltration<ul><li>e.g. <a href="/articles/sarcoidosis-1">sarcoidosis</a>, <a href="/articles/lymphoma">lymphoma</a>, leukaemia <sup>4,5</sup>- +<li>bronchovascular interstitial infiltration<ul><li>e.g. <a href="/articles/sarcoidosis-1">sarcoidosis</a>, <a href="/articles/lymphoma">lymphoma</a>, <a title="Leukaemia" href="/articles/leukaemia">leukaemia</a> <sup>4,5</sup>
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