Idiopathic interstitial pneumonias: HRCT chest approach

The approach to HRCT chest in patients with suspected idiopathic interstitial pneumonia (IIP) is with the aim to:

  • make sure an appropriate study requested i.e. HRCT chest with optimal individually adjusted protocol and ensure adequacy of the HRCT chest quality (see imaging protocol below)
  • meticulous scrutiny to detect all subtle findings, pattern, and distribution recognition as well as use of standard terminology in description of imaging findings
    • fibrotic changes
      • architectural distortion
      • traction bronchiectasis and bronchiolectasis
      • volume loss 
      • honeycombing
    • distribution of disease
      • central 
      • peribronchiovascular
      • peripheral - subpleural
      • patchy 
      • diffuse
      • subpleural sparing 
    • apicobasal gradient 
  • perhaps the most important role of radiologists is to differentiate the usual interstitial pneumonia (UIP) pattern of chronic fibrosing IIP from other subtypes and determine their level of confidence in the diagnosis as well as detecting features which help excluding IIP or suggesting other entities to be more likely
    • lung cysts
    • perilymphatic or centrilobular nodules
    • mosaic attenuation or air trapping
    • pleural thickening, plaques, calcification, or effusion 
    • dilated oesophagus
    • sparing of the lung bases
  • radiologists should always make a comparison with older study or studies; it cannot be emphasised enough the importance of reviewing all prior studies and not only the most recent one cause sometimes interval changes between two consecutive studies are too subtle to be conspicuous but comparison with the older images can be revealing
  • besides, sometimes vital pieces of clinical information such as exposure history (smoking, drugs, organic protein exposure, dust etc.), age, and gender are not provided by the physicians which could completely change the list of differentials or even final diagnosis radiologists come up with; hence, radiologists need to actively try to obtain as much relevant information as possible. This can be done by developing good rapport with referring physicians and quick search in hospital information system (HIS).

In 2013 ATS/ERS revision IIPs are assigned into following major groups. Each entity has its own imaging characteristics, disease behaviour, treatment and prognosis:

Imaging protocol 

Optimal imaging protocol for assessment of the IIP is crucial and it should be adjusted case based. Traditional non-contiguous HRCT chest is widely replaced by volumetric image acquisition mainly due to better assessment of the distribution, apicobasal gradient or patchiness of the disease, presence of bronchiectasis or pulmonary nodules. Ideal acquisition time is an end full inspiration when lungs reach their total lung capacity. Multi-detector HRCT chest with thin collimation and sharp preprocessing algorithm (bone algorithm) and thin (less than 2 mm) multiplanar reconstruction is desired. Prone images are helpful to exclude dependent atelectasis obscuring or mistaken for underlying peripheral fibrotic changes. Expiratory images, usually in non-contiguous acquisition, is crucial to assess air trapping which usually implies alternative diagnosis such as hypersensitivity pneumonitis rather than IIP.

Lower dose CT protocols may be used in follow-up scans of known or younger patients at the price of slightly lower image quality. Most patients undergo many studies for surveillance of their disease; hence, this can result in significant radiation dose reduction. Typically, lower mAs (~40 mA), non-contiguous technique, etc. are helpful methods.

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Article information

rID: 43552
System: Chest
Section: Approach
Synonyms or Alternate Spellings:

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