Tree-In-Bud Opacities In Lung

Tree-in-bud opacities are usually seen on a chest CT.  They are a description of an abnormality we see on imaging and do not describe a specific disease.  Tree-in-bud opacities can be seen in a variety of infections, lung diseases and cancer.

What do tree-in-bud opacities represent?

Tree-in-bud opacities means there is an abnormality involving the smallest air passages of the lungs or the small blood vessels in this region.

What does tree-in-bud look like on CT scan?

Tree-in-bud opacities on chest CT looks like small branching linear opacities and associated tiny nodules, usually less than 5 mm.  They are most predominant in the periphery of the lung.

Tree-in-bud nodularity

This refers to the tiny nodules associated with the branching opacities seen on CT. This can be another way of referring to the tree-in-bud pattern.

Differential diagnosis of tree-in-bud opacities

Infections

Infections that involve the small airways like tuberculosis, aspiration pneumonia, bacterial pneumonia, viral infections, and fungal infections can cause a tree-in-bud pattern.  This is one of the more common causes in practice.

Congenital disorders (conditions you are born with)

Cystic fibrosis is a disorder where the mucus produced in airways is thick and dry.  This results in reduced clearance of mucus and plugging or small and large airways.

Idiopathic disorders (conditions which have no known cause)

Obliterating bronchiolitis is a disease which can be idiopathic.  The small airways become blocked by scar tissue.  One of the predominant findings is tree-in-bud opacity from mucus being impacted in the small airways.  Some of the causes for this condition include prior infections, smoke inhalation, and post transplant.

Aspiration

Foreign material that gets into the lung can cause tree-in-bud opacities from an inflammatory reaction.

Immunologic and connective tissue disorders

Allergic bronchopulmonary aspergillosis, rheumatoid, and sjogren syndrome can have associated disease of the airways and tree-in-bud opacities as a feature of the disease.

Cancer

Spread of cancer to the small arteries in the lung can result in tree-in-bud opacities.

IV drug use

Fillers and particulate matter in injected drugs can cause a reaction in the lungs which results in tree-in-bud opacities.

Tree-in-bud symptoms

Since there are many causes, the symptoms will depend on the underlying cause.  Since infections and aspiration are the most common conditions, we will often see cough, fever, sputum production as symptoms.

What else can look like tree-in-bud?

The pattern has a classic appearance and is rarely mistaken.  There are multiple causes as outlined above.  Obtaining additional history and looking carefully for associated findings on the CT may be helpful in determining the cause.

Can tree-in-bud opacities be seen on chest X-ray?

No usually not.  The opacities are too small to be seen.

Is tree-in-bud dangerous?

It can be depending on the cause.

Tree-in-bud opacities may mean infection is located in the airways.  This can include infections like tuberculosis which require patient isolation and treatment.

Tree-in-bud opacities may also mean cancer is present and has spread to the small arteries.

Tree-in-bud treatment

Treatment will depend on the underlying cause.  Infections will be treated with antibiotics.  Cancer will need to be treated with systemic chemotherapy or radiation.

Tree-in-bud: summary

Tree-in-bud opacities are seen on chest CT.  They are small branching and nodular opacities which indicate disease of the small airways or arteries.  They are most  commonly seen with infections that involve the airways but have many causes.  The treatment will depend on the underlying cause.