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Thymus size evaluated by sonography. A longitudinal study on infants during the first year of life
H Hasselbalch1, D L Jeppesen, A K Ersbøll
1Department of Radiology, Hvidovre University Hospital, Copenhagen, Denmark.
Insights
Thymus size in healthy infants grows until 8 months, then shrinks. Breastfeeding and body size significantly influence thymus size, with illness having a lesser impact.
Area of Science:
- Pediatric imaging
- Immunology
- Infant development
Background:
- The thymus plays a crucial role in immune system development.
- Understanding thymus size variations in infants is important for assessing immune health.
- Previous studies have not comprehensively assessed thymus size dynamics in relation to infant-specific factors.
Purpose of the Study:
- To longitudinally assess thymus size in healthy infants using sonography.
- To investigate correlations between thymus size and clinical variables, including breast-feeding status and illness.
- To develop statistical models for estimating normal thymus size variation in infants up to one year of age.
Main Methods:
- Sonographic thymic index was used to estimate thymus volume in 47 healthy infants.
- Infants were examined neonatally and followed up at 4, 8, 10, and 12 months of age.
- Correlations between thymic index and infant sex, weight, length, illness, and breast-feeding status were analyzed.
Main Results:
- Thymus size increased from birth to 4 and 8 months, then decreased by 12 months.
- Thymic index showed positive correlations with infant body length and breast-feeding status.
- Exclusively breast-fed infants had larger thymic indices at 10 months; infants with fever had smaller thymic indices at 12 months.
Conclusions:
- Infant thymus size exhibits a dynamic growth pattern, peaking around 8 months.
- Breast-feeding status and body size are key determinants of thymus size variation.
- Illness has a less pronounced effect on thymus size, but significant correlations were observed.
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.
Material And 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).
Conclusion:
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.