22nd February 2024

Radiological evidence

Chest radiograph 

Most patients with bronchiectasis will have an abnormal chest radiograph. Although not diagnostic, common features include patchy lower zone opacification, linear atelectasis, and dilated and thickened airways (appearance of ‘tram lines’ / ring shadows).

Computed tomography (CT) 

High-resolution computed tomography (HRCT) is the gold standard imaging modality for confirming the diagnosis of bronchiectasis. Features of HRCT include:

• Airway dilatation can appear as a parallel / ‘tram line’ on chest X-ray. Dilated airways with accompanying pulmonary vessels can appear as  ‘signet rings’ on HRCT. Airway lumen dilatation of >1.5mm to adjacent pulmonary vessels is the classic diagnostic feature of bronchiectasis. 
• Smaller airways can present in a linear fashion, giving the appearance of a ‘tree in bud’ pattern on HRCT. 
• The distribution seen on HRCT  may be associated with different aetiologies of bronchiectasis:
  • The central (perihilar) pattern is more suggestive of allergic bronchopulmonary aspergillosis
  • Upper lobe distribution is significant for cystic fibrosis
  • Middle/lower lobe correlates with primary ciliary dyskinesis 
  • Lingula segment of the upper left lung with non-tuberculosis mycobacterium (NTM). 
• Airway visibility of 1cm around coastal pleural space or touching mediastinal pleura.