Absence of tubular myelin in lungs of infants dying with hyaline membrane disease.

Immaturity of the pulmonary surface active material synthesizing system with deficiency of surface active material in the premature lung is an accepted cause of hyaline membrane disease. Lamellar bodies, the intracellular form of surface active material, are produced and secreted from Type II pneumocytes and converted to tubular myelin in the alveolar lumen. Tubular myelin, in turn, gives rise to the surface monolayer, which has the greatest surface active property. Thus, lung sections were studied by light and electron microscopy from 35 infants who died of histologically confirmed hyaline membrane disease and 19 infants who died of other causes. Tubular myelin was not identified ultrastructurally in lungs of infants who died of hyaline membrane disease, despite the presence of abundant lamellar bodies. In contrast, 16 of 19 infants dying of other causes had easily identifiable tubular myelin in addition to lamellar bodies. The absence of tubular myelin in the hyaline membrane disease patients suggests an abnormality in the conversion of lamellar bodies to tubular myelin. The authors speculate that this abnormal lamellar body turnover may be important in the pathogenesis of hyaline membrane disease.