Acute thymic involution in fetuses and neonates with chorioamnionitis

Chorioamnionitis represents the leading cause of preterm birth and related pathologic conditions as well as of fetal death and frequently occurs in sy mptom-free mothers. Recent radiologic findings have indicated that thymus s ize is significantly reduced in preterm infants born to mothers with subcli nical, histologically proven chorioamnionitis. However, an accurate morphol ogic description of the thymus gland in fetuses and neonates with chorioamn ionitis is lacking, although it is known that infection and other stress pr ocesses may cause lymphocyte depletion in the thymuses of infants and older babies (acute stress involution). We describe morphologic modifications in the thymus of fetuses with histologically proven chorioamnionitis and newb orn infants with chorioamnionitis and proven sepsis. The main findings incl uded (1) decreased organ volume (ANOVA, P < .0024); (2) reduced corticomedu llary ratio (P < 10(-6)); (3) significant changes in the relationship betwe en thymic parenchyma and thymic interstitial tissue with resulting increase d organ complexity (P = .03); (4) severe reduction of thymocytes; and (5) o ther degenerative processes such as monocyte/macrophage infiltration of Has sall's bodies. These results indicate that chorioamnionitis, with or withou t sepsis, is associated with significant morphologic modifications in the t hymus. We wish to note that the described thymic pathology is only one aspe ct of the fetal systemic inflammatory response syndrome with which chorioam nionitis is associated. Copyright (C) 2000 by W.B. Saunders Company.