On HRCT, place the fibrosis (basal, peripheral, upper, peribronchovascular), name its features (reticulation, traction bronchiectasis, honeycombing), then assign the pattern: UIP, probable UIP, indeterminate, or an alternative diagnosis.
Orient first
- Honeycombing is clustered, subpleural cystic spaces with shared walls, usually in layers — not paraseptal emphysema and not traction bronchiectasis seen end-on.
- A UIP pattern is basal and subpleural predominant with honeycombing; probable UIP has the same distribution with traction bronchiectasis but no honeycombing.
- Features that suggest ANOTHER diagnosis: upper or mid-zone predominance, peribronchovascular distribution with subpleural sparing (NSIP), mosaic attenuation with air trapping (hypersensitivity pneumonitis), extensive ground glass, nodules, consolidation.
Acquire the study
- Volumetric thin-section non-contrast CT at full inspiration (supine), expiratory images for air trapping, and prone images to separate dependent atelectasis from early fibrosis.
The manoeuvre
- Axial and coronal: craniocaudal and axial distribution of the abnormality.
- Reticulation and traction bronchiectasis/bronchiolectasis on thin sections.
- Honeycombing: subpleural clustered cysts on the lung window, confirmed on sagittal and coronal reformats.
- Ground glass: its extent relative to fibrosis.
- Expiratory images: lobular air trapping (three or more lobules in more than one lobe suggests hypersensitivity pneumonitis).
- Prone images: dependent opacity that clears is atelectasis, not fibrosis.
- Extrapulmonary clues: oesophageal dilatation (scleroderma), pleural plaques (asbestosis), pulmonary artery size.
What confirms it
- A named pattern category (UIP / probable UIP / indeterminate / alternative) built from distribution plus features.
What licenses you to exclude it
- Absence of honeycombing does not exclude IPF — probable UIP in the right clinical context is often enough for the MDT.
The classic misread
- Calling paraseptal emphysema honeycombing.
- Calling dependent atelectasis fibrosis without prone images.
- Giving a single diagnosis instead of a pattern — the diagnosis is multidisciplinary.