Bronchiectasis is defined as localized bronchial dilatation.
The diagnosis of bronchiectasis is usually based on a combination of the following findings:
- bronchial dilatation (signet-ring sign)
- bronchial wall thickening
- lack of normal tapering with visibility of airways in the peripheral lung
- mucus retention in the broncial lumen
- associated atelectasis and sometimes air trapping
A signet-ring sign represents an axial cut of a dilated bronchus (ring) with its accompanying small artery (signet).
The most common cause of bronchiectasis is prior infection, usually viral, at an early age. 
It also occurs in patients with chronic bronchitis, COPD and cystic fibrosis. #Diagnosis #Radiology #Pulmonary #Bronchiectasis #Differential #RadiologyAssistant