Table 4. Definition and Subcategories of ILA (Modified from Hatabu et al. Lancet Respir Med 2020;8:726-737 [10]).

Definitions and subcategories of interstitial lung abnormalities

What are ILAs?

• Incidental identification of non-dependent abnormalities, including ground-glass or reticular abnormalities, lung distortion, traction bronchiectasis, honeycombing, and non-emphysematous cysts

• Involving at least 5% of a lung zone (upper, middle, and lower lung zones are demarcated by the levels of the inferior aortic arch and right inferior pulmonary vein

What are not ILAs?

Imaging findings restricted to:

• Dependent lung atelectasis

• Focal paraspinal fibrosis in close contact with thoracic spine osteophytes

• Smoking-related centrilobular nodularity in the absence of other findings

• Mild focal or unilateral abnormality

• Interstitial oedema (e.g., in heart failure)

• Findings of aspiration (patchy ground-glass, tree in bud)

Subcategories of ILAs

• Non-subpleural: ILAs without predominant subpleural localisation

• Subpleural non-fibrotic: ILAs with a predominant subpleural localisation and without evidence of fibrosis*

• Subpleural fibrotic: ILAs with a predominant subpleural localisation and with evidence of pulmonary fibrosis*

^*Fibrosis is characterised by the presence of architectural distortion with traction bronchiectasis or honeycombing (or both). ILAs = interstitial lung abnormalities