Thymic evolution on serial CT in glucocorticoid-treated pediatric pneumonia: a retrospective analysis

The pediatric thymus is sensitive to infection-related stress and glucocorticoid exposure, yet data remain limited on short-term thymic changes on paired chest CT before and after glucocorticoid-containing treatment for childhood pneumonia. This study evaluated changes in thymic transverse and anteroposterior diameters and CT attenuation on paired chest CT scans.

We retrospectively included 90 children with pneumonia who received glucocorticoid-containing therapy and had paired chest CT scans. Two radiologists independently measured the thymic transverse diameter, anteroposterior diameter, and CT attenuation before and after treatment. We used the Wilcoxon signed-rank test to compare pre- and post-treatment thymic parameters, and used age-stratified analysis, Spearman correlation, and multivariable linear regression to explore factors associated with thymic percentage changes.

After treatment, thymic transverse diameter decreased from 2.80 cm to 2.40 cm, anteroposterior diameter decreased from 1.20 cm to 0.70 cm, and CT attenuation decreased from 50.00 HU to 37.50 HU; all three parameters were significantly lower after treatment (all P < 0.001). Age-stratified analysis showed that each age group experienced significant reductions in these parameters, with no significant between-group differences in percentage changes. Dose-related analysis showed that cumulative methylprednisolone-equivalent dose and daily methylprednisolone-equivalent dose were weakly negatively correlated with the percentage change in thymic transverse diameter. However, multivariable linear regression indicated that dose metrics were not significantly associated with percentage changes in thymic transverse diameter, anteroposterior diameter, or CT attenuation.

In children with pneumonia receiving glucocorticoid-containing treatment, short-term follow-up CT showed reductions in thymic transverse diameter, anteroposterior diameter, and CT attenuation. Recognizing these possible short-term thymic changes may help pediatricians and radiologists avoid overinterpreting follow-up CT findings as anterior mediastinal lesions.Given the lack of a non-glucocorticoid control and the potential for severe pneumonia to induce thymic involution, causality cannot be inferred. Thus, thymic CT changes are not validated biomarkers of glucocorticoid exposure or immune function.