What is traction bronchiectasis?

Traction Bronchiectasis: Definition 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 This condition is a radiological finding that represents bronchial distortion resulting from surrounding retractile fibrosis rather than from infectious destruction of bronchial walls.

Pathophysiology and Mechanism

• Traction bronchiectasis occurs when fibrotic lung parenchyma pulls on adjacent bronchi, causing their dilation and distortion 1
• It is characterized by irregular bronchial and/or bronchiolar dilatation in areas of pulmonary fibrosis 1
• The contractile forces from surrounding fibrotic tissue create mechanical traction that permanently alters bronchial architecture 1
• Unlike infectious bronchiectasis, traction bronchiectasis is primarily a consequence of parenchymal fibrosis rather than primary airway inflammation 2

Radiological Features

• On High-Resolution CT (HRCT) scans, traction bronchiectasis appears as dilated bronchi within areas of fibrotic lung tissue 1
• Key radiological 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
  • Sometimes associated with abrupt kinking of bronchi by over 90 degrees in fibrotic areas 3

Clinical Context and Significance

• Traction bronchiectasis is an important radiological marker in fibrotic lung diseases, particularly in:

  • Idiopathic pulmonary fibrosis (IPF) 1
  • Fibrotic hypersensitivity pneumonitis 1
  • Connective tissue disease-associated interstitial lung disease 1
  • Post-tuberculosis lung damage 4

• It serves as a prognostic indicator in fibrotic lung diseases:

  • The presence and extent of traction bronchiectasis correlate with disease severity and prognosis 2
  • The traction bronchiectasis index (TBI) can stratify prognosis in patients with interstitial lung abnormalities 2

Relationship to Honeycombing

• Recent evidence suggests that traction bronchiectasis and honeycombing may represent a continuous spectrum of lung remodeling in IPF 5
• Pathologic-CT correlations show that honeycombing and traction bronchiectasis are closely related 1
• Honeycombing corresponds to bronchiolar cysts developed after collapse of fibrotic alveolar septa and dilatation of terminal airways 1
• The remodeling process appears to be a continuum from traction bronchiectasis to honeycombing in IPF 1

Diagnostic Approach

• HRCT scanning is the diagnostic procedure of choice to identify traction bronchiectasis 1
• Sensitivity and specificity of HRCT for detecting bronchiectasis exceeds 90% 1
• Identification of traction bronchiectasis on CT scans is associated with moderate interobserver agreement 1
• In patients with suspected interstitial lung disease, the presence of traction bronchiectasis helps distinguish fibrotic from non-fibrotic patterns 1

Clinical Implications

• In the context of interstitial lung disease, traction bronchiectasis is a key feature that suggests irreversible fibrosis 1
• It helps differentiate between different types of interstitial pneumonia patterns 3
• The presence of traction bronchiectasis in a probable UIP pattern on HRCT increases the likelihood of IPF diagnosis 1
• Unlike infectious bronchiectasis, management focuses on treating the underlying fibrotic lung disease rather than airway-directed therapies 4

Understanding traction bronchiectasis is crucial for accurate diagnosis, prognosis assessment, and management planning in patients with fibrotic lung diseases.