Paediatric Imaging

Hyaline membrane disease

(HMD), (also called idiopathic respiratory distress syndrome or respiratory distress syndrome). HMD is due to deficiency of alveolar surfactant. It is the most common life-threatening respiratory disorder of newborns. Most neonates with HMD are premature, but it occasionally occurs in infants greater than 36 weeks gestation. Other risk factors include infants of poorly controlled diabetic mothers, fetal asphyxia, maternal or fetal haemorrhage, and multiple gestations. It is more common and severe in males and more common in blacks than whites.

Surfactant is produced by type 2 alveolar cells which are present from about 24 weeks gestation. Deficiency of surfactant results in collapse of alveoli and the lungs becoming stiff. Increased respiratory effort is needed to inflate the lungs. There is exudation of plasma from the pulmonary capillaries into the alveolar space. This eventually organises to form a thick membrane which stains pink with standard histological preparations giving rise to the name "hyaline membrane disease".

Clinically, infants with HMD have respiratory distress which worsens during the first 18 - 24 hours of life, with gradual improvement generally starting by the third day. The chest radiograph will usually be abnormal by 6 hours of age. There is normal to decreased aeration of the lungs as compared to transient tachypnoea of the newborn where there is increased aeration. Initially there is fine reticular shadowing within the lungs with accentuation of the air bronchograms; as the condition progresses the lungs become more radiopaque (Fig.1). HMD (Fig.2) is a bilateral symmetrical disease. Asymmetric changes may be seen when some areas have been differentially aerated, for example misplaced endotracheal tube, asymmetric surfactant administration, localised pathology such as pulmonary interstitial emphysema, pulmonary haemorrhage or infection.

Treatment is supportive. Improvement depends on how quickly the baby is able to synthesise adequate amounts of endogenous surfactant and can take days to several weeks.

 

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Fig.1

(a) Mild hyaline membrane disease with increased fine reticular shadowing in the lungs. (b) Moderate HMD with coarser nodular shadowing.
Hyaline membrane disease, Fig.1 (a)
Hyaline membrane disease, Fig.1 (b)
Hyaline membrane disease, Fig.2