Compare each bronchus with its companion artery (bronchoarterial ratio), look for lack of tapering, then map the distribution — upper, lower, central or focal — because the distribution points to the cause.
Orient first
- Bronchiectasis is irreversible bronchial dilatation; the signs are an internal bronchial diameter larger than the adjacent artery (signet-ring sign), lack of tapering and bronchi visible within 1 cm of the pleura.
- Morphology: cylindrical (mild), varicose (beaded), cystic (saccular, clustered).
- Distribution suggests cause: upper lobe (cystic fibrosis, old tuberculosis), central (allergic bronchopulmonary aspergillosis), lower lobe (post-infective, immune deficiency, aspiration), middle lobe and lingula (non-tuberculous mycobacteria).
Acquire the study
- Non-contrast thin-section CT chest (1 mm or thinner) in full inspiration, with expiratory images for air-trapping when small airways disease is suspected.
The manoeuvre
- Axial lung window: bronchoarterial ratio in each lobe — the internal bronchial diameter against the adjacent artery.
- Follow bronchi toward the periphery on axial and coronal reformats: lack of tapering, and bronchi within 1 cm of the costal pleura.
- Wall thickening, mucus plugging and tree-in-bud nodules (active infection).
- Expiratory series: mosaic attenuation with air-trapping in small airways disease.
- Distribution lobe by lobe, and associated clues — high-attenuation mucus (ABPA), nodules and cavities (mycobacteria), situs inversus (primary ciliary dyskinesia).
What confirms it
- Bronchi larger than their arteries and failing to taper, in more than one segment, on thin-section CT.
What licenses you to exclude it
- Normal tapering and bronchoarterial ratios on thin-section CT exclude significant bronchiectasis.
The classic misread
- Calling bronchi dilated inside consolidation or collapse (reversible dilatation) — re-image after treatment.
- Missing traction bronchiectasis in fibrotic lung — it is a fibrosis sign, reported with the interstitial pattern.