Diverse histopathological patterns in Fleischner-defined interstitial lung abnormalities: Radiologic-Pathologic...

Area of Science:

• Pulmonary Medicine
• Radiology
• Pathology

Background:

• Interstitial lung abnormalities (ILA) are CT-detected findings that may indicate early interstitial lung disease (ILD).
• Histopathologic data correlating with ILA and ILD are limited, with prior studies yielding conflicting results.
• The 2025 American Thoracic Society (ATS) criteria aim to differentiate ILA from ILD.

Purpose of the Study:

• To examine the histopathological spectrum of Fleischner Society-defined ILA.
• To correlate histopathological findings with CT features and patient outcomes.
• To reclassify ILA cases based on the 2025 ATS criteria.

Main Methods:

• Retrospective analysis of 30 patients with surgical lung biopsies for ILA (2010-2021).
• Histopathological evaluation by three pulmonary pathologists and CT assessment by two radiologists.
• Comparison of overall survival between usual interstitial pneumonia (UIP)-related and non-UIP-related groups.

Main Results:

• Most patients (90%) had fibrotic ILA, predominantly reclassified as subclinical ILD (96.7%) per 2025 ATS criteria.
• Usual interstitial pneumonia (UIP) was the most common dominant pattern (43.3%), followed by nonspecific interstitial pneumonia (NSIP) and bronchiolocentric interstitial pneumonia (BIP) (20% each).
• CT findings included reticular opacity and traction bronchiectasis for UIP/NSIP, and branching linear opacities for BIP. No significant difference in overall survival was observed between UIP-related and non-UIP-related groups.

Conclusions:

• Fleischner-defined ILA, when reclassified by 2025 ATS criteria, is frequently subclinical ILD.
• The histopathology of ILA is heterogeneous, extending beyond UIP to include patterns like BIP.
• These findings underscore the importance of histopathological diversity in understanding ILA and its progression to ILD.