What is meant by the term cryptogenic organizing pneumonia (COP), and what are its imaging features?
The term COP is applied when organizing pneumonia is present without a clear etiology. Clinically, COP is characterized by months of low-grade fevers, cough, and malaise. Symptoms and imaging features typically rapidly improve with corticosteroid administration, although relapses can occur in 50% of cases.
COP has a wide variety of imaging manifestations, but it is most often characterized by chronic waxing and waning patchy lower lobe predominant airspace opacities, which are frequently peripheral and peribronchovascular in distribution. Ground glass opacities and nodules are common accompanying features. The appearance and clinical presentation can be confused with those of pneumonia, often leading to months of delayed appropriate management.