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Andrew B. Kairalla MD, Editor
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Small Thymus at Birth and BPD
Objective. Emerging evidence indicates a relationship between bronchopulmonary dysplasia (BPD) and chorioamnionitis. Recent data provide evidence of an acute thymic involution in very low birth weight (VLBW) preterm infants and fetuses with histologic chorioamnionitis. We tested the hypothesis that a small thymus detected at birth on the routine chest radiograph is a predictor of BPD in VLBW infants.
Methods. A prospective study was conducted on 400 VLBW preterm infants who survived >4 weeks (mean gestational age: 27.5 weeks [range: 24–30]; mean birth weight: 1010 g [range: 450-1450]). Thymic size was measured on routine chest radiographs taken in the first 6 hours after birth and expressed as the ratio between the transverse diameter of the cardiothymic image at the level of the carina and that of the thorax (CT/T). The accuracy of CT/T for identifying infants with BPD was tested using receiver operating characteristic curve analyses and multivariate logistic regression.
Results. Fifty-one VLBW infants (12.7%) subsequently developed BPD. A small thymus (CT/T <0.28) was observed in 94.1% of the infants with BPD versus 2.9% of the infants without BPD. A small thymus at birth identified infants with BPD with 94.1% sensitivity and 98.3% specificity (odds ratio: 17.8; 95% confidence interval: 5.7–55.4).
Conclusions. A small thymus at birth on the standard chest radiograph can accurately identify VLBW infants who subsequently develop BPD.
Comment. Acute fetal thymic involution has been associated with infection, inflammation, glucocorticoid use, and stress. We now learn that the finding of a narrow superior mediastinum (small thymus) on initial chest xray in VLBW infants is highly predictive of subsequent development of CLD. This gives us some new insight into the complex pathophysiology of CLD, and should help us identify premature infants at highest risk for this complication. ABK
Date: 18 Oct 2002
Time: 13:07:21
It is interesting to find that a small thymus at birth was able to identify
infants with BPD with 94.1% sensitivity and 98.3% specificity (odds ratio: 17.8;
95% confidence interval: 5.7–55.4). Small thymus is an indication of stressed
neonate that most likely the stress starts during the intrauterine life.
The question arises does the size of the thymus reflects the degree of stress?.
It will be interesting to correlate the causes of stress such as
infection, PROM, steroids etc. and the occurrence of small thymus at birth and
may be the time when the thymus regained its normal size and the
severity of BPD.
UserName: Saleh Al-Alaiyan
Institution: King Faisal Specialist Hospital & Research centre
telephone: 966-1-442 7765
email: alaiyan@kfshrc.edu.sa
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