Organizing Pneumonia

Organizing pneumonia (OP) is a nonfibrotic form of interstitial pneumonia that represents a manifestation of lung injury. It may be secondary to another process (such as vasculitis, collagen vascular disease, or drug therapy). When no inciting cause is found, the OP is believed to cryptogenic and the term Cryptogenic Organizing Pneumonia (COP) may be used clinically. Various patterns of OP may be encountered on imaging including classic (peripheral or bronchiolocentric consolidation), focal, crescentic, multinodular and fibrotic. The classic pattern is the most common, but the crescentic form (often known as the atoll or reverse halo sign) can be the most striking. The latter two patterns are more typical of OP associated with collagen vascular disease, most notably dermatomyositis and polymyositis.