Frequency of imaging phenotypes of pulmonary interstitial fibrosis

Our plain-English summary of Frequency of imaging phenotypes of pulmonary interstitial fibrosis, by W.T. Miller, S. Simpson, S. Sood, et al (SA Journal of Radiology, 2025).

The study

• Authors: W.T. Miller, S. Simpson, S. Sood, M. Hershman, C.R. Johnson, J.E. Schmitt, K.C. Patterson
• Journal: SA Journal of Radiology
• Published: 2025;29(1):3098
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Evaluation of diffuse interstitial lung disease (ILD) in thoracic imaging is complicated. Radiologists often use a pattern approach to interpretation; however, they are rarely aware of the statistical frequency of disease presentation.

Objectives: To evaluate the relative frequency of causes of fibrotic ILD as a function of imaging patterns.

Method: A CT database of 396 cases of fibrotic ILD was amassed from an institutional diffuse lung disease registry and retrospective search of medical records. Three radiologists and one pulmonologist independently and blindly reviewed the CT scans for the distribution of fibrosis, predominant feature and non-pulmonary findings.

Results: Peripheral fibrosis was most common (291/396, 73.5%), usually caused by idiopathic pulmonary fibrosis (IPF) and connective tissue diseases-related interstitial lung disease (CTD-ILD) but occasionally by hypersensitivity pneumonitis (HP), idiopathic nonspecific interstitial pneumonia (iNSIP) and asbestosis. Peripheral fibrosis with honeycombing was usually IPF and without honeycombing, was usually CTD-ILD. Peripheral fibrosis with pleural plaques was always asbestosis. Peripheral fibrosis with oesophageal dilatation was usually connective tissue diseases. Consolidative-like peripheral fibrosis was CTD-ILD. Axial fibrosis (61/396, 15.4%) was usually sarcoidosis, HP, CTD-ILD or silicosis. Axial fibrosis with predominantly consolidative-like fibrosis, honeycombing, or reticulation was usually sarcoidosis. Axial fibrosis predominated by ground glass opacity was usually HP or CTD-ILD. Lymph node calcification or short axis > 17 mm increased the probability that axial fibrosis was due to sarcoidosis. The non-specific fibrosis phenotype was uncommon (44/396, 11.1%), usually CTD-ILD (25/44, 57%) but also HP, IPF, iNSIP or asbestosis.

Conclusion: Patterns of lung fibrosis provide guidelines to identify the cause.

Contribution: A flow diagram that predicts the relative frequency of the causes of 10 patterns of ILD.

© 2025. The Authors.

In plain English

This study reviewed chest CT scans of 396 patients with scarring (fibrotic) interstitial lung disease at the University of Pennsylvania, taken from a lung disease registry and a medical records search. Three radiologists and one lung specialist, blinded to diagnoses, classified where the scarring lay. Scarring mainly at the lung edges (peripheral fibrosis) was most common, in 291 of 396 cases, mostly from idiopathic pulmonary fibrosis or connective tissue disease. Asbestosis was diagnosed in 9 of 396 cases. The records search, aimed at rare diseases, mainly added pneumoconioses such as asbestosis. Asbestosis accounted for 4 of 114 peripheral cases with honeycombing and 3 of 142 without. Peripheral fibrosis with pleural plaques had 100% specificity and 100% positive predictive value for asbestosis. Scarring around the airways (axial fibrosis), seen in 61 of 396 cases, was most often sarcoidosis. The authors concluded that the pattern helps estimate the relative likelihood of each cause. They noted that many diagnoses lacked biopsy confirmation and that rare diseases were oversampled.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective imaging study. CT scans were drawn from an institutional lung disease registry and a medical records search, then anonymised, randomised and read independently by four readers blinded to clinical information except age and sex.
• Who was studied: 396 cases of interstitial lung disease with fibrotic features at the University of Pennsylvania Medical Center, Philadelphia, United States. Cases came from a diffuse lung disease registry begun in January 2013 (369 cases) and from radiology record searches covering 2013 to 2018, and 2001 to 2018 for some rare diseases (27 cases).
• Exposure: No asbestos exposure, fiber type or dose was assessed. The study compared CT patterns of fibrosis across diagnoses. Asbestosis was one of the diagnoses, and the records search for rare diseases, which included the search term 'asbestosis', mainly added pneumoconiosis cases.
• Main results:
  • Peripheral fibrosis was the most common consensus pattern, in 291 of 396 cases (73.5%). Among these 291, idiopathic pulmonary fibrosis caused 146 (50.2%) and connective tissue disease-related ILD caused 106 (36.4%).
  • Asbestosis accounted for 9 of the 396 cases (2.3%) in the whole database, and 1 of the 369 registry cases (0.3%) (Table 1).
  • In Table 3, all 9 asbestosis cases had the peripheral fibrosis pattern (100%).
  • Peripheral fibrosis with honeycombing (UIP pattern) was seen in 114 of 256 peripheral cases (44.5%). Idiopathic pulmonary fibrosis caused 73 of these 114 (64.0%). Asbestosis caused 4 of the 114.
  • Among 142 peripheral fibrosis cases without honeycombing, connective tissue disease-related ILD caused 72 (51.0%), idiopathic pulmonary fibrosis 48 (34.0%) and hypersensitivity pneumonitis 10 (7.0%). Asbestosis caused 3.
  • Peripheral fibrosis with pleural plaques had 100% specificity and 100% positive predictive value for asbestosis (p less than 0.0001).
  • Peripheral fibrosis with a dilated oesophagus had 97% specificity and 78% positive predictive value for connective tissue disease-related ILD.
  • Axial fibrosis accounted for 61 of 396 cases (15.4%). Sarcoidosis caused 36 of these 61 (59.0%), hypersensitivity pneumonitis 8 (13.1%), pneumoconiosis 7 (11.5%) and connective tissue disease-related ILD 6 (9.8%).
  • In axial fibrosis, a lymph node abnormality (calcification or short axis greater than 17 mm) had 76% sensitivity and 95% specificity for sarcoidosis when pneumoconiosis could be excluded on clinical grounds.
  • Nonspecific fibrosis was seen in 22 of 396 cases (5.6%). It was most often caused by connective tissue disease-related ILD (9 of 22, 41%).
  • The readers had moderate (kappa 0.41 to 0.60) to substantial (0.61 to 0.80) agreement on the fibrosis pattern.
• The authors' conclusion: The authors concluded that fibrotic lung diseases overlap considerably on imaging, but that the imaging phenotype (peripheral, axial or nonspecific) is useful in determining the relative probability of the causative diseases.
• Limitations the authors state:
  • Many cases lacked histologic (biopsy) confirmation because of the medical centre's practice patterns.
  • Retrospectively collected cases may have introduced unclear biases, and they artificially raised the frequency of rare diseases, especially pneumoconiosis.
  • As a tertiary referral centre series, the results may overemphasise uncommon diseases compared with primary care and community centres.
  • The extent of honeycombing was not assessed.
  • Readers agreed less on the dominant fibrosis feature, with no consensus in 89 of 396 cases (22.5%).

Topics

Medical terms in this study, explained in our Lexicon: Interstitial Fibrosis, Interstitial Lung Disease, CT Scan, Fibrosis, Idiopathic, Pulmonary Fibrosis, Pneumonitis, Interstitial.

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