Diagnostic HRCT criteria for usual interstitial pneumonia (UIP) pattern - ATS/ERS/JRS/ALAT (2011(2018)

As a part of international evidence-based guidelines adopted by a collaborative effort of the American Thoracic Society (ATS), the European Respiratory Society (ERS), the Japanese Respiratory Society (JRS), and the Latin American Thoracic Association (ALAT), specific diagnostic HRCT criteria for usual interstitial pneumonia (UIP) pattern were adopted in 2011 and reviewed in 2018. These criteria have been shown to have moderate interobserver reliability among thoracic radiologists ⁴. 

In 2018, the Fleischner Society has also published an updateda white paper on the approach for the HRCT diagnosis of usual interstitial pneumonia: diagnostic HRCT criteria for usual interstitial pneumonia (UIP) pattern - Fleischner society guideline (2018). 

Overview 

• the guideline is intended to help clinicians make an accurate diagnosis of IPF and to empower them to implement recommended courses of action, particularly decisions in which diagnostic intervention to pursue
• the guideline applies for the patterns and distribution assessed on HRCT chest
• these criteria have been shown to have moderate interobserver reliability among thoracic radiologists ⁴

Classification

• UIP pattern (definite)
• possibleprobable UIP pattern
• inconsistentindeterminate for UIP pattern
• alternative diagnosis 

This helps radiologists to determine the certainty of usual interstitial pneumonia (UIP) diagnosis diagnosis based on HRCT chest findings. The importance of this guideline is that (definite)definite UIP pattern on chest HRCT precludes the need for tissue diagnosis ^1,2-2,5. However, unfortunately up to 20% of inconsistent with UIP group (or actually atypical UIP) can be UIP on biopsy or progress clinically to a diagnosis idiopathic pulmonary fibrosis (IPF).

UIP pattern

All four features presentClassic HRCT pattern including:

1. subpleural, basal predominance
2. reticular abnormality
• honeycombing: it is the distinguishing feature of UIP and must be present
  • +/- traction bronchiectasis
• reticular abnormalities
• distribution: subpleural with a basal predominance
• absence of features listed as "inconsistent with UIP pattern" (see below)

PossibleProbable UIP pattern

All three features presentHRCT studies with absent honeycombing, but showing:

• reticular abnormalities 
  • +/- groundglass opacification superimposed on a fine reticular pattern (cf. pure groundglass opacities, which is not a typical UIP feature)
• peripheral traction bronchiectasis or traction bronchioloectasis 
• distribution: subpleural, with a basal predominance
• reticular abnormality
• absence of features listed as "inconsistent with UIP pattern" (see below)

Inconsistent withIndeterminate for UIP pattern

Any oneHRCT features of pulmonary fibrosis that do not meet the following seven"UIP" or "probable UIP" patterns above and does not explicitly suggest an "alternative diagnosis".

• subtle reticular abnormalities 
  • +/- groundglass opacification superimposed on a fine reticular pattern (cf. pure groundglass opacities, which is not a typical UIP feature)
• distribution: do not suggest any specific aetiology 

This category includes those patients with very limited subpleural reticulation or groundglass opacities without other obvious features presentof pulmonary fibrosis and for whom there is some suspicion for an early UIP or probable UIP. 

Alternative diagnosis 

Although there is clinical suspicion for IPF, HRCT findings are suggestive of another aetiology (e.g. hypersensitivity pneumonitis, NSIP, sarcoidosis).

Previous versions

In 2018 the guidelines were reviewed, and the main changes compared to the 2011 publication are:

• upper or mid-lung predominance"possible UIP" no longer exists and has been replaced by "probable UIP"
  • studies have shown that most of these patients were likely to have histopathologic UIP pattern despite the radiologic absence of honeycombing 
• peribronchovascular predominancesimilar to the diagnostic HRCT criteria for usual interstitial pneumonia (UIP) pattern - Fleischner society guideline (2018), this reviewed guidelines moved from three to four HRCT categories with a reasonable correspondence among the two 2018 papers 
• extensive ground-glass abnormality (i.e. more than reticular abnormality)now, the patient's management should be based on their HRCT classification in two groups ⁵:
  • HRCT pattern of probable UIP, indeterminate for UIP, and alternative diagnosis
  • profuse micronodules (bilateral, predominantly upper lobes)HRCT pattern of UIP
  • discrete cysts (multiple, bilateral, away from honeycombing)
• diffuse mosaic attenuation / air-trapping (bilateral in ≥3 lobes)
• consolidation in bronchopulmonary segment(s) or lobe(s)

See also

• ATS criteria for the diagnosis of UIP on pathology

• diagnostic categories of UIP pattern based on HRCT chest- Fleischner society guideline 2018

Diagnostic HRCT criteria for usual interstitial pneumonia (UIP) pattern - ATS/ERS/JRS/ALAT (2011)