PULMONARY HYALINE MEMBRANES IN NEWBORN INFANTS

Abstract

The results of statistical, morphologic and experimental studies on the nature, occurrence and significance of hyaline (asphyxial) membranes seen in the lungs of infants who die in the neonatal period are presented. Analysis of material from 509 consecutive autopsies on newborn infants, together with analysis of the infants' histories, shows that these membranes occur most commonly in premature infants and in more mature infants with a history of a complication of pregnancy, labor or delivery capable of causing fetal anoxia. These hyaline membranes are not seen in stillborn infants nor in infants living less than one hour. They appear to cause atelectasis, by blocking the mouth of alveoli, and to be a major cause of death in the neonatal period. Studies on vernix, meconium and amniotic fluid indicate that these hyaline membranes are not formed of vernix or meconium, but of the concentrated protein of aspirated amniotic fluid. A rise in the squamous cell content of amniotic fluid during the third trimester of pregnancy is demonstrated; this may explain the difference in microscopic appearance between hyaline membranes formed of amniotic fluid which is aspirated before this rise in squamous cells takes place and those containing squamous cells which are seen if the fluid is aspirated after this increase occurs. The membranes are demonstrated to be independent of pulmonary hemorrhage, edema or inflammation and not to be formed of degenerated airway epithelium. Similar membranes were produced experimentally by repeated intratracheal injection of small amounts of amniotic fluid into the excised respiratory tracts of animals while the lungs were alternately expanded and contracted for one hour. The time and volume factors necessary for successful experimental production of these membranes are discussed. The significance of pulmonary hyaline membranes in the production of neonatal atelectasis is indicated. No instances of "congenital alveolar dysplasia" were found in the 509 cases reviewed, and evidence that it may not be a valid clinical and pathologic entity is presented.