FIG. 8.

Constrictive and obliterative bronchiolitis. (A) Obliterative bronchiolitis is the pathologic correlate of the clinical diagnosis of bronchiolitis obliterans syndrome (BOS). Histologically, it is characterized by fibrous obliteration of small airways, typically leaving a “footprint” of peripheral airway smooth muscle (*). Increased periairway macrophages and cholesterol clefts are common findings secondary to small airway obstruction. Potential etiologies include post-viral syndromes, chronic aspiration, chronic airway rejection in the setting of lung transplant, and graft-versus-host disease in the setting of bone marrow transplant. Asthma and cystic fibrosis occasionally produce focal obliterative bronchiolitis. (B) Constrictive bronchiolitis refers to partial obliteration (stenosis) of small airways and is a common finding in the spectrum of BOS. This lung biopsy from a child with chronic aspiration demonstrates increased subepithelial collagen and elastin (*) on Movat's pentachrome stain.