Why RDS is Called Hyaline Membrane Disease
Respiratory distress syndrome is called hyaline membrane disease because the pathological hallmark of this condition is the formation of eosinophilic, proteinaceous "hyaline membranes" that line the alveoli and terminal airways of affected premature infants. 1, 2
Pathological Basis for the Name
The term "hyaline membrane disease" derives directly from the microscopic appearance of the lungs in affected infants:
Hyaline membranes consist primarily of fibrin, proteinaceous debris, and cellular material that accumulate in the alveolar spaces and coat the alveolar walls, creating a characteristic glassy (hyaline) appearance under microscopy 3
These membranes form during the early exudative phase (days 1-5) of RDS through a cascade of events: basement membrane disruption, denudation of alveolar epithelial cells, leakage of serum proteins into airways due to high alveolar capillary permeability, and subsequent fibrin deposition 1, 4
The hyaline membrane formation blocks small airways and impairs gas exchange, contributing to the severe dyspnea, tachypnea, and unremitting hypoxemia that characterize the clinical syndrome 1, 5
Clinical-Pathological Relationship
The two terms—RDS and hyaline membrane disease—represent different perspectives on the same condition:
"Respiratory distress syndrome" describes the clinical presentation (the symptoms and signs observed at the bedside) 2
"Hyaline membrane disease" describes the pathological findings (what is seen under the microscope in lung tissue) 2
Both terms are used interchangeably because the clinical syndrome of RDS in premature infants reliably correlates with the histologic finding of hyaline membranes 2
Underlying Mechanism
The formation of hyaline membranes is triggered by surfactant deficiency in immature lungs:
Surfactant deficiency leads to alveolar instability and collapse, capillary leak edema, and ultimately hyaline membrane formation 2
High alveolar capillary permeability allows serum proteins to leak into airways, where they inhibit any remaining surfactant function and contribute to membrane formation 6, 4
The severity of hyaline membrane formation correlates with disease severity, though modern surfactant replacement therapy has reduced the extent of hyaline membrane formation compared to the pre-surfactant era 7
Evolution of Understanding
The relationship between clinical presentation and pathology has been refined over time:
Historically, the presence of hyaline membranes was the defining pathological feature that gave the disease its name 3
In the modern era with surfactant therapy, hyaline membrane formation is less severe and occurs later in the clinical course, but the terminology persists 7
The term RDS has become more commonly used in clinical practice, while hyaline membrane disease remains important for understanding the underlying pathophysiology 2