Chest CT findings of follicular bronchiolitis: Comparative analysis according to underlying lung diseases.

Objectives Follicular bronchiolitis (FB) is a rare and often under-recognized small airway disease characterized by lymphoid hyperplasia in the bronchiolar walls. We aimed to compare chest CT findings in patients with FB by underlying disease: rheumatoid arthritis (RA), Other connective tissue diseases (CTDs), and those without CTD. Methods A retrospective cohort of patients with pathologically-proven follicular bronchiolitis was classified into three groups: RA (n = 9), Other CTDs (n = 6), and non-CTD (n = 13). Chest CT were reviewed for findings including tree-in-bud nodules and air trapping (small airway disease), ground glass opacities, fibrosis, and bronchiectasis. Chi-square test was performed to evaluate the frequency differences across three groups. Fisher's exact test was performed to compare RA group and non-RA group. Results In all patients, the most common CT finding was bronchiectasis (17/28, 61 %), followed by small airway disease features (14/28, 50.0 %), fibrosis (13/28, 46.4 %), and ground glass opacities (7/28, 25.0 %). In three-group comparison (RA vs. Other CTD vs. non-CTD), small airway disease was significantly more prevalent in other CTD (3/6, 50.0 %) and non-CTD (10/13, 76.9 %) groups compared to the RA group (1/9, 11.1 %) (p = 0.01). In two-group analysis (RA vs. non-RA), fibrosis (7/9, 77.8 % vs. 6/19, 31.6 %; p = 0.041) and bronchiectasis (8/9, 88.9 % vs. 9/19, 47.4 %; p = 0.049) were significantly more common in the RA group compared to non-RA patients. Conclusion Chest CT findings of FB vary significantly depending on the underlying disease. Small airway disease features predominate in non-RA patients, while patients with RA and FB more frequently show fibrosis and bronchiectasis, likely reflecting coexistent pulmonary manifestations of RA. Recognizing these imaging patterns may improve diagnostic accuracy and inform appropriate management.