Hyaline Membrane Disease (Respiratory Distress Syndrome) (HMD) (RDS)

Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed

Etiology/Pathophysiology:
Preterm infants have pulmonary immaturity which results in a surfactant deficiency. Surfactant lowers the surface tension of the alveolar membrane. Without surfactant the alveoli collapse at the end of each expiration. This in turn leads to respiratory failure in the neonate. In older infants surfactant deficiency can arise when they develop asphyxia/shock and acidosis.

Pathology:
Generalized capillary leak and mucosal necrosis leads to the small air filled terminal airways, the respiratory bronchioles and alveolar ducts, being surrounded by collapsed alveoli filled with debris in a near uniform distribution, and this leads to the classic "ground glass" appearance on the chest x-ray.

Imaging Findings:
Radiographic changes usually appear shortly after birth, but can be delayed for 12-24 hours. The classic "ground glass" appearance consists of a bilaterally symmetrical homogeneously stippled pattern of fine lucencies (air bronchograms) interspersed with linear densities that causes the heart and diaphragm contours to become obscured. The patient usually has a decreased lung volume, and vertically oriented ribs leading to a bell shaped thorax. The classical symmetrical appearance will most probably not be present in patients who have received artificial surfactant therapy.

DDX:

• Meconium Aspiration - usually has nodular non homogeneous densities, may have pleural effusions, usually has an increased lung volume.
• Neonatal pneumonia - usually has non homogeneous densities, may have pleural fluid, usually has a normal lung volume.
• Transient Tachypnea of the Newborn - usually has non homogeneous densities, may have pleural fluid.

References:
See References Chapter.

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