Acute fibrinous and organizing pneumonia (AFOP) is a recently described pattern of lung injury that has a mortality rate similar to that of diffuse alveolar damage (DAD) and likely represents a variant histology. The pattern lacks classic histologic features seen in other histologic patterns of lung injury associated with an acute or subacute clinical presentation, namely, DAD, eosinophilic pneumonia, and organizing pneumonia.

AFOP may have an acute or subacute clinical presentation and is associated with a variety of underlying conditions (infection, collagen vascular disease, environmental exposure) or may be idiopathic. The mortality rate is approximately 50%, although some patients present with a more indolent clinical course with good recovery. AFOP likely represents a variant histology of DAD, but further investigation is needed.