Sex Difference in Normal Thymic Appearance in Adults 20–30 Years of Age

PURPOSE: To determine whether there is a sex difference in the appearance of the normal thymus in 20-30-year-old men and women. MATERIALS AND METHODS: This retrospective study was approved by the institutional review board and was compliant with HIPAA. The requirement for informed consent was waived. Images and medical records of 238 consecutive subjects without known thymic disease (175 men, 63 women) who underwent chest computed tomography with intravenous contrast material in 2008 were reviewed. Average thymic region of interest (ROI), subjective assessment of thymic attenuation by using a scale of grades 0-3, thymic anteroposterior measurement, and mean maximal thymic lobe thickness were recorded by two independent thoracic radiologists, blinded to subject age and sex. Thymic morphologic characteristics were assessed in consensus. The two-sided Wilcoxon rank-sum test, Student t test, test for linear regression, analysis of covariance, two-way factorial analysis of variance, and continuity-adjusted χ(2) test were used for statistical analysis. RESULTS: There was a significant sex difference in thymic attenuation as measured objectively by using mean thymic ROI measurement (P < .0001) and subjectively by using a scale of grades 0-3 (P < .0001), which held true when corrected for age (P < .0001). A sex difference was also found in regard to the rate of decrease in mean thymic attenuation with age, with men's thymuses exhibiting a significant decrease in attenuation during the decade, unlike women (P = .0479). There was no significant sex difference in mean maximal thymic lobe thickness (P = .8697). A quadrilateral, as opposed to triangular, configuration of the thymus was more common in women than men (P = .0034). CONCLUSION: There is a significant sex difference in normal thymic appearance in 20-30-year-old men and women. The thymus of 20-30-year-old women typically exhibits higher attenuation and more commonly exhibits a quadrilateral configuration.