What are tree-in-bud nodules in the lung?

From the Guidelines

Tree-in-bud nodules in the lung are a radiographic finding that represents inflammation and mucus plugging in the small airways, often associated with infectious bronchiolitis, and can be identified on high-resolution CT scans as a branching pattern resembling a budding tree. These nodules are typically a sign of small airway disease, which can be caused by a variety of factors, including infections, underlying systemic disorders, and concerning exposures 1. The diagnosis of tree-in-bud nodules requires a comprehensive medical history, physical examination, physiologic testing, and radiographic studies, including high-resolution CT scans with expiratory cuts 1. Some key features of tree-in-bud nodules include:

• Nodular branching of 2 to 4 mm
• Linear branching “tree-in-bud” abnormalities
• Airway wall thickening
• Dilation of the small airways These findings can be indirect signs of bronchiolar disease, and the absence of these features cannot rule out the disease 1. In the correct clinical setting, HRCT findings of direct features, such as small nodules and tree-in-bud pattern, and indirect features, such as mosaic attenuation on expiratory scanning, may obviate the need for further invasive testing 1. However, surgical lung biopsy and bronchoscopy may still be necessary to provide a pathologic classification and rule out infection in some cases 1. Treatment of tree-in-bud nodules targets the underlying cause, which can include antibiotics, antifungals, or management of underlying conditions. The development of tree-in-bud nodules is thought to occur due to inflammation and secretions filling the small bronchioles and alveolar ducts, creating the distinctive branching pattern visible on high-resolution CT scans.

From the Research

Definition of Tree-in-Bud Nodules

• Tree-in-bud (TIB) nodules are a radiologic pattern seen on high-resolution chest CT, reflecting bronchiolar mucoid impaction occasionally with additional involvement of adjacent alveoli 2.
• The TIB pattern consists of small centrilobular nodules of soft-tissue attenuation connected to multiple branching linear structures of similar caliber that originate from a single stalk 3.

Etiology of Tree-in-Bud Nodules

• The microbiologic etiology of TIB pattern is similar to that of the general population, with infectious causes being the most common, including bacterial, fungal, viral, or parasitic infections 2.
• Other causes of TIB pattern include immunological, congenital, and idiopathic disorders, as well as aspiration or inhalation of toxic agents 4.
• Malignant conditions, such as central lung cancer, can also present with a TIB pattern, particularly in cases of squamous cell carcinoma 5.

Characteristics of Tree-in-Bud Nodules

• TIB pattern is characterized by obstructive bronchial mucoid impaction distal to the cancer, followed by consolidation and ground-glass opacities 5.
• The pattern is usually confined to the areas of lung supplied by the involved bronchi and has a focal distribution predominantly 5.
• Pathologically, TIB pattern correlates with bronchiolectasis, bronchiolar lumen filled by mucus and inflammatory exudates, wall thickening with inflammatory cells infiltration 5.

Clinical Significance of Tree-in-Bud Nodules

• TIB pattern can be an important diagnostic finding in patients with lung disease, and its recognition can help prevent diagnostic errors 3.
• A full understanding of TIB pattern can be useful in guiding further diagnostic evaluation and management, particularly in cases where the etiology is unclear 2, 4.