Normal thymus in adults: appearance on CT and associations with age, sex, BMI and smoking.
OBJECTIVE
To investigate CT appearance and size of the thymus in association with participant characteristics.


METHODS
2540 supposedly healthy participants (mean age 58.9 years, 51 % female) were evaluated for the CT appearance of thymic glands with four-point scores (according to the ratio of fat and soft tissue), size and morphology. These were correlated with participants' age, sex, BMI and smoking history.


RESULTS
Of 2540 participants, 1869 (74 %) showed complete fatty replacement of the thymus (Score 0), 463 (18 %) predominantly fatty attenuation (Score 1), 172 (7 %) half fatty and half soft-tissue attenuation (Score 2) and 36 (1 %) solid thymic gland with predominantly soft-tissue attenuation (Score 3). Female participants showed less fatty degeneration of the thymus with higher thymic scores within age 40-69 years (P < 0.001). Participants with lower thymic scores showed higher BMI (P < 0.001) and were more likely to be former smokers (P < 0.001) with higher pack-years (P = 0.04).


CONCLUSIONS
Visual assessment with four-point thymic scores revealed a sex difference in the fatty degeneration of the thymus with age. Women show significantly higher thymic scores, suggesting less fat content of the thymus, during age 40-69 years. Cigarette smoking and high BMI are associated with advanced fatty replacement of the thymus.


CONCLUSIONS
74% of participants (mean age 58.9 years) demonstrated complete fatty thymus. Women show less fatty thymus compared to men at ages 40-69 years. Smoking and high BMI are associated with advanced fatty degeneration in thymus.
Department of Radiology, Center for Pulmonary Functional Imaging, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St., Boston, MA, 02215, USA. taraki@partners.org.|Department of Radiology, Kinki University Faculty of Medicine, Osaka-Sayama, Japan. taraki@partners.org.
Tetsuro
T
Araki
Department of Radiology, Center for Pulmonary Functional Imaging, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St., Boston, MA, 02215, USA.
Mizuki
M
Nishino
Department of Biostatistics, Boston University School of Public Health, Boston, MA, USA.
Wei
W
Gao
Department of Biostatistics, Boston University School of Public Health, Boston, MA, USA.|The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA.
Josée
J
Dupuis
The Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
Gary M
GM
Hunninghake
Department of Radiology, Kinki University Faculty of Medicine, Osaka-Sayama, Japan.
Takamichi
T
Murakami
The Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
George R
GR
Washko
The National Heart Lung and Blood Institute's Framingham Heart Study, Framingham, MA, USA.|Pulmonary Center and Department of Medicine, Boston University School of Medicine, Boston, MA, USA.
George T
GT
O'Connor
Department of Radiology, Center for Pulmonary Functional Imaging, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St., Boston, MA, 02215, USA.
Hiroto
H
Hatabu
D000328:Adult; D000367:Age Factors; D000368:Aged; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012727:Sex Characteristics; D012907:Smoking / Q000473:pathology*; D013950:Thymus Gland / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
Adult; Body mass index; Computed tomography; Smoking; Thymus gland