Interstitial lung abnormalities (ILAs) are incidental findings on CT scans, potentially indicating early stages of interstitial lung disease. These abnormalities often remain unnoticed as they appear on scans primarily performed for non-respiratory indications, such as abdominal or thoracoabdominal imaging. Despite being asymptomatic at the time of detection, ILAs are linked to serious clinical outcomes, including reduced lung function, higher risk of respiratory diseases and increased mortality. A recent review published in Radiology examined the prevalence and reporting rates of ILAs in a routine clinical setting, aiming to understand their progression and impact on patient outcomes. The findings underscore the need for a systematic approach to recognising ILAs in non-targeted scans.
The Prevalence of ILAs in Clinical CT Scans
Among 21,118 patients aged 50 and above undergoing abdominal or thoracoabdominal CT scans, 1.7% were found to have ILAs. Thoracoabdominal scans had a higher detection rate (2.1%) compared to abdominal scans (1.3%), reflecting the increased lung coverage provided by the former. Notably, the majority of these scans were performed for non-respiratory purposes, such as trauma assessment, oncology staging or evaluation of abdominal complaints. The incidental detection of ILAs highlights the diagnostic potential of these imaging procedures, even when they are not specifically targeting the lungs.
ILAs were further classified into subpleural fibrotic, subpleural non-fibrotic and non-subpleural types. Subpleural fibrotic ILAs were the most common subtype, accounting for 54.4% of cases. These findings were often characterised by traction bronchiectasis, architectural distortion and other fibrotic features visible on CT scans. Notably, the study found that older patients and males were more likely to present with ILAs, aligning with previous research suggesting an age- and sex-related predisposition. The overall prevalence of ILAs in this study was lower than in some previous reports, potentially due to the inclusion of abdominal-only scans that limit the visibility of lung abnormalities in upper and middle regions.
Underreporting of ILAs in Routine Practice
A major issue identified in the study was the significant underreporting of ILAs. Nearly 44% of ILAs went unreported in the original radiology interpretations. This underreporting was particularly pronounced for subpleural non-fibrotic ILAs, with over half of such cases being overlooked. The underreporting rates were also higher in abdominal CT scans compared to thoracoabdominal ones, likely due to the narrower lung field coverage and the primary focus of these scans on abdominal organs.
Several factors contribute to the high rates of underreporting. First, the clinical focus of abdominal and thoracoabdominal CT scans is often non-pulmonary, leading radiologists to prioritise findings relevant to the referring clinician's concerns, such as abdominal pathology or tumour staging. Second, the subtle nature of early ILAs, especially non-fibrotic subtypes, makes them harder to detect without high-resolution imaging or dedicated chest CT protocols. Finally, a lack of awareness regarding the clinical implications of ILAs at the time of original reporting may have played a role, particularly as much of the study data predated widespread recognition of ILAs as significant prognostic indicators.
Underreporting has profound implications for patient care. ILAs are not benign findings; their progression is associated with worsening respiratory function, development of fibrosis and increased mortality risk. The study’s findings underscore the need for radiologists to systematically assess the lung parenchyma on abdominal and thoracoabdominal CT scans, even when these areas fall outside the primary diagnostic focus.
Clinical Implications of ILAs: Progression and Mortality Risk
The clinical consequences of ILAs are significant, with a high rate of progression observed among affected individuals. In follow-up scans of patients with ILAs, 37.6% demonstrated definite progression, and an additional 10.2% likely progressed. Key risk factors for progression included the presence of fibrotic features such as traction bronchiectasis, which increased the likelihood of disease progression by more than threefold. These findings emphasise the need for regular monitoring of patients with ILAs, particularly those with fibrotic characteristics.
The study also revealed a stark association between ILAs and mortality. Patients with fibrotic ILAs had a fourfold higher risk of death from respiratory causes compared to those without ILAs. Even non-fibrotic ILAs were associated with increased all-cause mortality, highlighting the prognostic significance of these findings irrespective of fibrotic features. The risk of progression from non-fibrotic to fibrotic ILAs further supports the need for early identification and follow-up.
ILAs were particularly common in older patients, who may already face an elevated risk of respiratory and cardiovascular diseases. This overlap of risk factors complicates the clinical management of ILAs, necessitating a multidisciplinary approach involving pulmonologists, radiologists and general practitioners. Awareness of the clinical implications of ILAs can lead to earlier interventions, potentially mitigating progression and improving outcomes.
The incidental detection of interstitial lung abnormalities on abdominal and thoracoabdominal CT scans offers an opportunity for early identification of interstitial lung disease. Despite their prognostic significance, ILAs remain underreported in routine clinical practice, reflecting gaps in radiological focus and awareness. The findings highlight the importance of systematically assessing lung bases in all CT scans, including these regions. Subpleural fibrotic ILAs, in particular, demand attention due to their strong association with disease progression and respiratory-related mortality.
Given the growing recognition of ILAs as a marker of potential interstitial lung disease, radiologists play a crucial role in early detection. Incorporating protocols that ensure thorough evaluation of lung findings in abdominal and thoracoabdominal CT scans can bridge current gaps in reporting. Additionally, high-resolution follow-up imaging and multidisciplinary collaboration are essential for managing patients with ILAs and improving long-term outcomes. By addressing the challenges of underreporting and raising awareness of the clinical implications of ILAs, healthcare providers can take a proactive approach to mitigating their impact on patient health.
Source: Radiology
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