Thymus size and its relationship to perinatal events

A retrospective study was conducted to assess radiographically the thymus size in well and sick
neonates and to search for a possible relationship to perinatal events. Thymus size was expressed
as cardiothymic:thoracic ratio (CT/T) by measuring the width of the cardiothymic shadow at the
level of carina and dividing it by the width of the thorax at the costophrenic angles. The CT/T was
measured on chest radiographs obtained on day 1 in well term neonates consecutively born in our
nursery and sick neonates with meconium staining of the amniotic fluid, meconium aspiration
syndrome or respiratory distress syndrome (RDS). Neonates with congenital anomalies, congenital
heart disease or intrauterine growth retardation were excluded. There were no significant relationships
between CT/T and sex, birth route, birthweight or gestational age in well and sick term
neonates. The CT/T were comparable among well and sick term neonates and were significantly
greater in the preterm neonates with RDS than in the preterm neonates without RDS. The CT/T
was correlated to the birth route only in the preterm neonates.
We conclude that thymus involution in the perinatal period is a complex process and the response is
different between term and preterm neonates.