CT Quantification of Interstitial Lung Abnormalities and Changes of Age-related Pathomorphology

Background Interstitial lung abnormalities (ILA) are associated with further disease progression, increased mortality risk, and decline in lung function in the elderly, which deserves enough attention.Objective The objective of this study was to quantify the extent of interstitial lung abnormalities (ILA) in a non-smoking asymptomatic urban cohort in China using low-dose CT (LDCT) and to analyze the age-related pathological changes.Methods We retrospectively analyzed clinical data and chest LDCT images from a cohort of 733 subjects who were categorized into 3 groups: 18-39, 40-59, and >= 60 years old according to age. Furthermore, we selected 40 cases of wax-embedded lung tissue blocks archived after pulmonary bullectomy and the same age groups were categorized. Four representative CT signs of ILA, including interlobular septal thickening (ILST), intralobular interstitial thickening (ILIT), ground-glass opacity (GGO), and reticular shadow (RS), were semi-quantified based on the percentage of the affected area. The scores and distribution of four CT signs of ILA were compared between different sex and age groups. The age-related pathological changes were analyzed.Results The ILA findings were found predominantly in the lower lobes and the subpleural region. The semi-quantitative scores of four CT signs in all subjects under 40 were 0. However, in subjects over 40 years old, the scores gradually increased with age, although most of them remained low. The size of the alveoli increased, the number of alveoli decreased, the alveolar septum became thinner, and the number of ATII cells increased with age. A statistically significant difference was observed among the different age groups (chi 2=50.624, P=0.033; chi 2=80.000, P=0.043; chi 2=33.833, P=0.000; chi 2=13.525, P=0.031). The macrophage population and the percentage of collagen fibers in the alveolar septum increased, while the percentage of elastic fibers decreased with age. There was no significant difference among the different age groups (chi 2=19.817, P=0.506; chi 2=52.419, P=0. 682; chi 2=54.868, P=0.518).Conclusion When the four CT signs mentioned above are in the upper central area, and the score has a medium or high score, it is crucial to determine the underlying pathological causes. ILA may be the result of chronic lung injury.