Recognize fibrotic ILD features on HRCT scans

You have an essential role in diagnosing fibrotic ILDs, as early diagnosis requires radiologist interpretation of HRCT1–4


Chest HRCT is the gold standard for early and accurate diagnosis of fibrotic ILDs5

In diagnosing ILDs, there are four general features to be considered that indicate the presence of pathological abnormalities on HRCT scans and are important to the interpretation of HRCT scans:6

  • Reticular opacities
  • Nodules
  • Increased lung opacity (high attenuation)
  • Decreased lung opacity (low attenuation)

HRCT features of UIP and NSIP patterns commonly found in fibrotic ILDs7,8

HRCT features of UIP and NSIP patterns commonly found in fibrotic ILDs7,8



Sourced from: Imaging Atlas of ILDs

72-year-old man with UIP. HRCT shows diffuse reticulations, and traction bronchiectasis and bronchiolectasis.

  • Abnormal and irregular dilation of the bronchi/bronchioles due to respiratory tract inflammation (sometimes reversible) or pulmonary fibrosis
  • On a HRCT scan, it appears as an increase in the calibre of the distal respiratory tract (no reduction in the diameter peripherally, visibility in the subpleural lung at least 20 mm from the pleura)
  • On the scan, they present as tubular or cystic airspaces depending on the orientation of the bronchi in the cross-section
  • Differentiating between traction bronchiectasis and honeycomb is sometimes difficult on axial cross-sections. Sagittal or coronal cross-sections and the minIP are usual
Diagnostic orientation
  • Traction bronchiectasis is associated with signs of fibrosis



Sourced from: Imaging Atlas of ILDs

Subpleural honeycombing forming several layers of cysts in a 73-year-old man with UIP.

  • Clustered cystic airspaces with well-defined walls, measuring 2–10 mm in diameter, sometimes reaching 25 mm, usually in subpleural regions
Associated signs with honeycombing
  • Intralobular reticulation
  • Traction bronchiectasis and bronchiolectasis
  • Loss of lobar volume
  • Fissured distortion



Sourced from: Imaging Atlas of ILDs

Marked intralobular reticulations in the two lung bases without honeycombing. Note the relative lung savings immediately under pleura, pointing to a NSIP.

  • Small linear or curved intralobular opacities measuring less than 10 mm forming an irregular reticulation
  • They can be isolated or associated with other signs
Diagnostic orientation

If the intralobular reticulations are posterior and inferior subpleural reticulations

  • Usual interstitial pneumonia (UIP, probable UIP, indeterminate for UIP, alternative diagnosis of UIP) / Connective tissue disease (CTD)
  • Non-specific interstitial pneumonia (NSIP)
  • Desquamative interstitial pneumonia (DIP)

If intralobular reticulations are associated with ground-glass opacity

  • Hypersensitivity pneumonitis (HP), alveolar proteinosis



Sourced from: Imaging Atlas of ILDs

Ground-glass opacity associated with intralobular reticulations and bronchiectasis. Radiological pattern consistent with NSIP. No honeycombing.

  • Slightly increased attenuation of lung parenchyma, with preservation of vascular and bronchial margins
Diagnostic orientation

Ground-glass opacity can be associated with various conditions:

  • Pulmonary oedema
  • Pulmonary infection: pneumocystis jirovecii pneumonia, cytomegalovirus (CMV), etc.
  • Hypersensitivity pneumonitis (HP)
  • Respiratory bronchiolitis
  • Desquamative interstitial pneumonia (DIP)
  • Acute interstitial pneumonia (AIP)


Improve your ability to diagnose fibrotic ILDs.
This atlas can assist you through the process of diagnosing an ILD, helping you recognize key clues and characteristics on chest HRCT and histopathology cuts from surgical lung biopsy.



Patients’ clinical history can assist you in:3
  • Contributing to multidisciplinary team discussion
  • Interpreting radiological features on HRCT scans
  • Making a differential diagnosis of suspected ILD

Factors to consider when considering a differential diagnosis in patients with suspected ILD3

Factors to consider when considering a differential diagnosis in patients with suspected ILD

Adapted from: Chung J, Goldin J. Lung. 2018;196(5):561–567.

Recognize the most telling aspects of patients’ clinical history to aid interpretation of HRCT scans and consider differential diagnosis of 
suspected ILD3


HRCT is important for the assessment of the extent of ILD and to enable assessment of progression of fibrotic ILD on follow-up imaging4

Criteria for PPF as employed in the ATS/ERS/JRS/ALAT guidelines9


Criteria for PPF as employed in the ATS/ERS/JRS/ALAT guidelines9

ALAT, Asociación Latinoamericana de Tórax; ATS, American Thoracic Society; ERS, European Respiratory Society; JRS, Japanese Respiratory Society; PPF, progressive pulmonary fibrosis.


Radiological evidence of disease progression

Radiological evidence of disease progression is defined as (one or more of the 

  • New/increased honeycombing
  • Increased lobar volume loss
  • Increased extent/coarseness of increased lobar volume loss
  • New fine reticulation
  • Increased extent/severity of traction bronchiectasis and bronchiolectasis


Be alert to the criteria defining PPF, as you have an important role in recognizing the radiological evidence of disease progression4,9


AIP, acute interstitial pneumonia; ALAT, Asociación Latinoamericana de Tórax; ATS, American Thoracic Society; CMV, cytomegalovirus; CTD, Connective tissue disease; DIP, desquamative interstitial pneumonia; ERS, European Respiratory Society; HP, hypersensitivity pneumonitis; HRCT, high-resolution computed tomography; ILD, interstitial lung disease; JRS, Japanese Respiratory Society; NSIP, non-specific interstitial pneumonia; PPF, progressive pulmonary fibrosis; UIP, usual interstitial pneumonia.

  1. Cottin V, Hirani N, Hotchkin D, et al. Presentation, diagnosis and clinical course of the spectrum of progressive-fibrosing interstitial lung diseases. Eur Respir Rev. 2018;27(150):180076.
  2. Cottin V, Valenzuela C. Diagnostic approach of fibrosing interstitial lung diseases of unknown origin. Presse Med. 2020;49(2):104021.
  3. Chung J, Goldin J. Interpretation of HRCT scans in the diagnosis of IPF: improving communication between pulmonologists and radiologists. Lung. 2018;196(5):561–567.
  4. Mohning MP, Richards JC, Huie TJ. Idiopathic pulmonary fibrosis: the radiologist’s role in making the diagnosis. Br J Radiol. 2019;92(1099):20181003.
  5. Chowaniec M, Skoczyńska M, Sokolik R, Wiland P. Interstitial lung disease in systemic sclerosis: challenges in early diagnosis and management. Reumatologia. 2018;56(4):249–254.
  6. Elicker B, de Castro Pereira CA, Webb R, Leslie KO. High-resolution computed tomography patterns of diffuse interstitial lung disease with clinical and pathological correlation. J Bras Pneumol. 2008;34(9):715–744.
  7. Torres PPTES, Rabahi MF, Moreira MADC, et al. Importance of chest HRCT in the diagnostic evaluation of fibrosing interstitial lung diseases. J Bras Pneumol. 2021;47(3):e20200096.
  8. Gotway MB, Freemer MM, King TE Jr. Challenges in pulmonary fibrosis. 1: Use of high resolution CT scanning of the lung for the evaluation of patients with idiopathic interstitial pneumonias. Thorax. 2007;62(6):546–553.
  9. Raghu G, Remy-Jardin M, Richeldi L et al. Idiopathic Pulmonary Fibrosis (an update) and progressive pulmonary fibrosis in adults. An Official ATS/ERS/JRS/ALAT Clinical Practice Guideline. Am J Respir Crit Care Med. 2022;205:e18–e47.

Resources for patients