Thymus size evaluated by sonography. A longitudinal study on infants during the first year of life.
OBJECTIVE
To use sonography in a follow-up study aimed at assessing the size of the thymus in healthy infants, and to search for a possible relation to clinical variables, breast-feeding status, and illness.


METHODS
Forty-seven healthy infants were examined as neonates and re-examined at 4 months of age. Thirty-seven of the infants were also re-examined at 8, 10, and 12 months of age. The thymus size was measured with the sonographic thymic index used as a volume estimate. The correlations between the thymic index and the sex, weight, length, illness, and breast-feeding status of the infants were analysed.


RESULTS
At birth the median thymic index was 12 (range 4-29). At 4 months the median thymic index was 28 (range 12-83). The thymic index was positively correlated to the body length of the infant and to its breast-feeding status (p < 0.0001). At 8 months the median thymic index was 29 (range 6-55) and most of the variation could be explained by the length of the infant (p = 0.0018, r = 0.50). At 10 months the median thymic value had decreased to 19 (range 9-49), and at 12 months to 17 (range 7-53). Infants exclusively breast-fed during the first 4 months of their lives had a larger thymic index at 10 months than formula-fed infants (p = 0.0024). Infants with fever episodes from 10 to 12 months had a smaller thymic index at 12 months (p = 0.0241).


CONCLUSIONS
The thymus size in healthy infants increases from birth to 4 and 8 months of age and then decreases. Most of the individual variation can be explained by breast-feeding status and body size, and to a lesser extent by illness. We propose statistical models by which the normal variation/distribution of the thymic size can be estimated in infants up to one year of age.
Hasselbalch
H
H
Department of Radiology, Hvidovre University Hospital, Copenhagen, Denmark.
Jeppesen
D L
DL
Ersbøll
A K
AK
Engelmann
M D
MD
Nielsen
M B
MB
D000367:Age Factors; D001824:Body Constitution; D001942:Breast Feeding; D005260:Female; D005334:Fever / Q000473:pathology; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D012737:Sex Factors; D013950:Thymus Gland / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000254:growth & development; D014463:Ultrasonography