From the Guidelines
Usual interstitial pneumonia (UIP) on CT scan is characterized by a definite UIP pattern that includes subpleural and basal predominant reticular abnormalities with honeycombing, often with traction bronchiectasis, and an absence of features inconsistent with UIP, as described in the most recent guidelines 1. The CT criteria for UIP include a subpleural and basal predominant distribution, often heterogeneous, with honeycombing with or without traction bronchiectasis, and an absence of features inconsistent with UIP, such as upper or mid-lung predominance, peribronchovascular predominance, extensive ground-glass opacities, profuse micronodules, discrete cysts, diffuse mosaic attenuation, or consolidation in bronchopulmonary segments 1. Key features of UIP on CT scan include:
- Subpleural and basal predominant reticular abnormalities
- Honeycombing with or without traction bronchiectasis
- Absence of features inconsistent with UIP
- Heterogeneous distribution with normal lung areas interspersed with fibrotic changes
- Probable UIP lacks honeycombing but shows the other features
- Indeterminate for UIP shows fibrotic changes without the typical distribution or honeycombing These criteria are important because a definite UIP pattern on CT may obviate the need for surgical lung biopsy in appropriate clinical contexts, allowing for earlier diagnosis and management of idiopathic pulmonary fibrosis, as supported by the American Thoracic Society guidelines 1. In clinical practice, it is essential to consider these CT criteria for UIP to ensure accurate diagnosis and management of patients with idiopathic pulmonary fibrosis, and to prioritize morbidity, mortality, and quality of life as the primary outcomes.
From the Research
CT Criteria for Usual Interstitial Pneumonia (UIP)
The CT criteria for UIP include:
- Reticular abnormality and honeycombing with basal and peripheral predominance 2
- Honeycombing as a predominant feature, which has a predictive value of 90% for UIP 3
- Spatially inhomogeneous, bilateral, peripheral, basal-predominant pattern of reticular opacities and honeycombing with little if any ground-glass attenuation 3
- Subpleural and patchy distribution of honeycombing 3, 4
- Reticular pattern and bronchiectasis on HRCT, with a cranial-caudal increase in patients with histologically verified UIP 4
- Lower-lobe honeycombing on HRCT, with an odds ratio of 11.45 for UIP 5
- Upper-lung irregular lines on HRCT, with an odds ratio of 6.28 for UIP 5
- Absence of ground glass opacities on HRCT, which is associated with a higher likelihood of UIP 4, 6
Key Features
Some key features that distinguish UIP from other interstitial lung diseases include:
- Presence of honeycombing, which is a strong predictor of UIP 3, 2, 5
- Reticular abnormality and traction bronchiectasis, which are common in UIP 4, 6
- Basal and peripheral predominance of reticular abnormality and honeycombing 3, 2, 6
- Absence of features suggestive of an alternative diagnosis, such as ground glass opacities or mosaic attenuation 4, 6
Diagnostic Accuracy
The diagnostic accuracy of CT criteria for UIP is high, with a sensitivity of 74%, specificity of 81%, and positive predictive value of 85% when using lower-lung honeycombing and upper-lung irregular lines as independent predictors 5. Additionally, a confident CT diagnosis of UIP is correct in 88% of cases, and the correctness of a CT diagnosis made at intermediate or high confidence is 88% 3.