Traction Bronchiectasis: Definition, Pathophysiology, and Clinical Significance
Traction bronchiectasis is the permanent dilation of bronchi caused by the contractile force of surrounding fibrotic lung tissue, which exerts traction and expands the diameter of the involved airways. 1
Definition and Pathophysiology
- Traction bronchiectasis occurs when fibrotic lung parenchyma pulls on adjacent bronchi, causing their dilation and distortion, creating mechanical traction that permanently alters bronchial architecture. 1
- Unlike other forms of bronchiectasis, traction bronchiectasis is specifically caused by the contractile forces from surrounding fibrotic tissue rather than primary airway inflammation or infection. 1
- It represents a key radiological marker in fibrotic lung diseases, indicating irreversible structural changes in the bronchial tree due to surrounding parenchymal fibrosis. 1, 2
Radiological Features
- On High-Resolution CT (HRCT) scans, traction bronchiectasis appears as dilated bronchi within areas of fibrotic lung tissue. 1
- Key diagnostic features include:
- Enlarged internal bronchial diameter where bronchi appear larger than accompanying arteries (signet ring sign) 1
- Irregular bronchial dilatation in a background of reticulation and/or ground-glass attenuation 1
- Dilated bronchi that can be tracked back toward more central bronchi on contiguous HRCT sections 1
- Right-angled traction bronchiectasis (abrupt kinking of a bronchus by over 90 degrees or an abrupt angle close to 180 degrees of branching bronchi) is a specific subtype that can help differentiate idiopathic pulmonary fibrosis (IPF) from nonspecific interstitial pneumonia (NSIP). 3
Clinical Context and Significance
- Traction bronchiectasis serves as an important radiological marker in various fibrotic lung diseases, particularly in: 1
- Idiopathic pulmonary fibrosis (IPF)
- Fibrotic hypersensitivity pneumonitis
- Connective tissue disease-associated interstitial lung disease
- The presence and extent of traction bronchiectasis correlate with disease severity and prognosis in patients with interstitial lung abnormalities. 1, 2
- The traction bronchiectasis index (TBI) can be used to stratify prognosis in patients with interstitial lung abnormalities. 2
- In the context of interstitial lung disease, traction bronchiectasis suggests irreversible fibrosis and increases the likelihood of IPF diagnosis when seen in a probable UIP pattern on HRCT. 1
Diagnostic Approach
- HRCT scanning is the diagnostic procedure of choice for identifying traction bronchiectasis, with sensitivity and specificity exceeding 90%. 1
- Minimum intensity projection (MinIP) images can improve visualization and detection of right-angled traction bronchiectasis, enhancing diagnostic accuracy. 3
- Identification of traction bronchiectasis helps distinguish fibrotic from non-fibrotic patterns in interstitial lung disease. 1
- Pathologically, traction bronchiectasis reflects a subpleural predominance of fibrosis and is associated with extensive reticular opacity on imaging. 3
Distinction from Other Forms of Bronchiectasis
- Unlike post-infectious bronchiectasis, traction bronchiectasis is primarily a consequence of parenchymal fibrosis rather than primary airway inflammation or infection. 1, 4
- Post-TB bronchiectasis can include both traction bronchiectasis (radiological sequelae) and bronchiectasis with an inflammatory bronchial component and opportunistic infections. 4
- Some researchers suggest that traction bronchiectasis and honeycombing in IPF represent different aspects of a continuous spectrum of lung remodeling rather than distinct entities. 5
Clinical Implications
- The presence of traction bronchiectasis indicates irreversible structural changes and is associated with poorer prognosis in fibrotic lung diseases. 1, 2
- Recognition of traction bronchiectasis is crucial for accurate diagnosis and classification of interstitial lung diseases, particularly in distinguishing IPF from other fibrotic lung disorders. 1, 3
- Management focuses on treating the underlying fibrotic lung disease rather than the bronchiectasis itself, as the bronchial dilation is a consequence rather than the primary pathology. 1