T he recognition of the importance of interstitial lung abnormality (ILA) at CT emerged from the systematic evaluation of large cohorts, showing a prevalence of 4%-9% in cigarette smokers and a prevalence of 2%-7% in never-smokers (Table 1) (1-9). Individuals with ILA have an increase in symptoms such as chronic cough and shortness of breath, decreased total lung capacity, reduced exercise capacity, and increased all-cause mortality. ILA may progress and may represent subclinical or early pulmonary fibrosis (Table 2) (10-16).A recent Fleischner position paper provided an updated definition of ILA, with descriptive terms, a summary of risk factors and clinical outcomes, and a proposed schema for management (2). Our purpose is to provide a practical guide for radiologists regarding ILA that includes the definition of and terms for ILA, outcomes, possible strategies for clinical management, and future directions.
Entities Not Considered ILAPotential chest CT pitfalls and overlaps in ILA are summarized in Table 3. Although centrilobular nodularity (Fig 5) was included in initial descriptions of ILA The clinical importance of interstitial lung abnormality (ILA) is increasingly recognized. In July 2020, the Fleischner Society published a position paper about ILA. The purposes of this article are to summarize the definition, existing evidence, clinical management, and unresolved issues for ILA from a radiologic standpoint and to provide a practical guide for radiologists. ILA is a common incidental finding at CT and is often progressive and associated with worsened clinical outcomes. The hazard ratios for mortality range from 1.3 to 2.7 in large cohorts. Risk factors for ILA include age, smoking status, other inhalational exposures, and genetic factors (eg, gene encoding mucin 5B variant). Radiologists should systematically record the presence, morphologic characteristics, distribution, and subcategories of ILA (ie, nonsubpleural, subpleural nonfibrotic, and subpleural fibrotic), as these are informative for predicting progression and mortality. Clinically significant interstitial lung disease should not be considered ILA. Individuals with ILA are triaged into higher-and lower-risk groups depending on their risk factors for progression, and systematic follow-up, including CT, should be considered for the higher-risk group. Artificial intelligence-based automated analysis for ILA may be helpful, but further validation and improvement are needed. Radiologists have a central role in clinical management and research on ILA.
