Organizing pneumonia: cryptogenic and disease associated.

Organizing pneumonia is defined by the presence of buds of granulation tissue (fibroblastic cells and connective matrix) within the alveolar lumen, usually associated with proliferative bronchiolitis obliterans. It may result from several causes, but cryptogenic organizing pneumonia is a distinct clinicopathologic entity with characteristic clinical and imaging features. Typical COP is thus easily recognized by the clinician, and the diagnosis is made by the finding of organizing pneumonia on lung biopsy specimen. The response to corticosteroids is rapid and complete usually without sequelae, but relapses occur frequently and prolonged corticosteroid treatment is often necessary.