963 THYMUS SIZE AND ITS RELATIONSHIP TO RESPIRATORY DISTRESS SYNDROME

Abstract

In an attempt to correlate the thymolytic effect of glucocorticoids with their role in the induction of surfactant synthesis and the prevention of RDS, the size of the thymus on the initial chest radiographs of newborns who required intensive care was reviewed. Utilizing a ratio of the cardiothymic silhouette at the carina to the thoracic width (C-T/T) we found an increase in C-T/T with increasing gestational age. Newborn infants with RDS had a significantly elevated mean C-T/T (0.40 vs 0.36; p. <0.001) an increased percentage of ‘enlarged’ (C-T/T ≥ 0.45) thymuses (28% vs 8% in non-RDS babies), and a decreased percentage of ‘small’ (C-T/T ≥ 0.30) thymuses (11% vs. 26%). Moreover, in a series of 8 multiple gestations that were discordant for RDS, the larger thymus was seen in those with RDS in 6 of 8, while in only one did the converse hold true. Surprisingly, babies whose mothers had received prepartum dexamethasone to prevent RDS showed no difference in thymic size when compared to a control population. These data are consistent with the theory that endogenous gluco-corticoids play a physiologic role in the prevention of RDS. The initial size of the thymus may also be of predictive value in differentiating between the diverse causes of respiratory distress in newborn infants.