Radiology Features

All patients with suspected IPF should undergo high-resolution computed tomography (HRCT) evaluation.^1-3 HRCT allows a detailed examination of the lung parenchyma.²

An HRCT for evaluating ILD should follow guidelines for improving diagnostic results.³

• Non-contrast
• Thin collimation (≤/2 cm), short rotation time, highest pitch for motion-free scan
• Number of acquisitions in proper position (3):
  1. Supine, sustained end-inspiration
  2. Supine, entire thorax at sustained end-expiration after prolonged expiration (volumetric or sequential acquisition)
  3. Volumetric or sequential image (can be limited to lower lobes) to clear position-induced changes
• Scan for new ground-glass changes, acute pulmonary embolism via CT angiography with/without non contrast HRCT

UIP PATTERN

There are 4 categories of usual interstitial pneumonia (UIP) pattern based on HRCT findings.

The 2018 ATS/ERS/JRS/ALAT guidelines define 4 categories for diagnosing UIP based on the presence or absence of specific HRCT features.³

The HRCT criteria were devised to convey a level of confidence for a radiologic diagnosis of UIP in a patient with clinical features that suggest a diagnosis of IPF.⁴

HRCT in IPF

The distribution and predominance of specific features on HRCT scans are key factors in determining UIP patterns.⁵

UIP: Criteria

HRCT criteria for usual interstitial pneumonia. The features necessary for a UIP diagnosis are:^3,6

• Subpleural and basal predominance (distribution is often heterogeneous)
  AND
• Honeycombing with or without peripheral traction bronchiectasis/bronchiolectasis

UIP: Example

UIP shows:^3,6

• Subpleural and basal predominant distribution
• Honeycombing
• Traction bronchiectasis

The distribution of UIP is characteristically basal and peripheral, though often patchy.^1,3,5,6

Image courtesy of and used with permission from Robert Suh, MD.

Honeycombing is critical for an HRCT diagnosis of UIP without surgical biopsy.^1,3,5-7

In cases of UIP, ground-glass opacities (GGO) may be present but should be less extensive than the reticulation.^1,3,6 Mediastinal lymphadenopathy may be present.³

PROBABLE UIP

Criteria

Criteria for a diagnosis of probable UIP:^3,6

• Subpleural and basal predominance (often heterogeneous distribution)
  AND
• Reticular pattern with peripheral traction bronchiectasis/bronchiolectasis
  AND
• May have mild ground-glass opacities

Example

Lacking honeycombing, probable UIP exhibits bronchiectasis and may have histopathologic signs of UIP upon biopsy. Surgical biopsy therefore may aid in IPF diagnosis.³

Note the lack of honeycombing in this image.

HRCT image of possible usual interstitial pneumonia. Reprinted from Fishman‘s Pulmonary Diseases and Disorders. 4th edition 2007. Meltzer EB and Noble PW: Chapter 70, Idiopathic Pulmonary Fibrosis.¹⁰ Used with permission from McGraw-Hill Companies. Inc. Copyright © 2007 McGraw-Hill Companies. Inc.

Surgical lung biopsy is not always possible. A surgical biopsy may be deferred due to underlying comorbidities, poor pulmonary function, or patient preference.^1,3

INDETERMINATE FOR UIP

Criteria

Criteria for a diagnosis of indeterminate for UIP:^3,6

• Subpleural and basal predominance
  AND
• Subtle reticulation, may have ground-glass opacity (mild) or distortion (“early UIP pattern”)
  AND
• Distribution or features of fibrosis not consistent with specific etiology (“truly indeterminate”)

Example

When characteristics suggestive of fibrosis are visible on HRCT scans but do not meet the criteria of UIP or probable UIP, the images should be classified as indeterminate for UIP.⁵ UIP pattern may be found on histological testing of patients with HRCT patterns indeterminate for UIP.^3,6

Image courtesy of and used with permission from Robert Suh, MD.

ALTERNATIVE DIAGNOSIS

The presence of any of these features should lead to the consideration of an alternative diagnosis.^3,6

CT Features:

• Mosaic attenuation
• Predominant GGO
• Consolidation
• Cysts, nodules (profuse or centrilobular)

Predominant Distribution:

• Peribronchovascular
• Perilymphatic
• Upper or mid-lung

Other:

• Pleural plaques (consider asbestosis)
• Extensive lymph node enlargement
• Distal clavicular erosions (consider rheumatoid arthritis)
• Dilated esophagus, pleural effusions, pleural thickening (consider connective tissue disease)

Upper-lung predominance

Image courtesy of and used with permission from David A Lynch, MD

Peribronchovascular predominance

Image courtesy of and used with permission from David A Lynch, MD

Extensive ground-glass abnormalities

Image courtesy of and used with permission from David A Lynch, MD

Profuse perilymphatic micronodules

Image courtesy of and used with permission from David A Lynch, MD

Discrete cysts

Image courtesy of and used with permission from Robert Suh, MD

Diffuse mosaic attenuation/air trapping

Image courtesy of and used with permission from David A Lynch, MD

Consolidation in bronchopulmonary segment(s)/lobe(s)

Image courtesy of and used with permission from David A Lynch, MD

HRCT is not always enough to diagnose IPF

Patients who are clinically suspected of having IPF with HRCT features of either probable UIP, indeterminate UIP, or alternative diagnosis should undergo additional diagnostic evaluation.³