Hyaline membrane disease. I. Cellular changes.

Cellular changes were studied in 1 μ thick sections of lungs from 84 perinatal deaths, including 44 with hyaline membrane disease (HMD). The presence or absence of osmiophilic granules was related to surface tension measurements in 69 cases. The presence of numerous granules usually indicated normal surfactant and their absence a lack. It is concluded that the granules represent surfactant material. Osmiophilic granules were found first at 20 weeks' gestation (in 2 out of 6 fetuses). After 24 weeks' gestation almost all infants had many granules, except those with HMD. The earliest stages in hyaline membrane formation consisted of interstitial oedema accompanied by localized areas of necrosis and desquamation of alveolar epithelial cells. Osmiophilic granules were virtually absent. Infants dying at a later stage of the disease showed more extensive hyaline membranes, but from 36 hours almost all cases displayed some signs of repair of the denuded alveolar surfaces. In 5 out of 10 cases with evidence of repair, normal values for surface tension were obtained. In the late stages of HMD some of the cells lining the alveoli were highly abnormal. They consisted of large thick squames with very few capillaries in apposition to them; the appearances were thus consistent with a severe degree of alveolo-capillary block.