Cryptogenic organizing pneumonia (COP) is a distinct histopathologic entity characterized by Masson bodies which are intraalveolar buds of granulation tissue; consisting of connective tissue and myofibroblasts. This pathologic pattern when present with the characteristic imaging and clinical features of COP defines the diagnosis of the disease. A specific etiology is not found. Treatment with corticosteroids results in a rapid clinical and imaging improvement but unfortunately relapses are common upon decreasing the dose or stopping the treatment. This case report describes a typical case of COP with the characteristic improvement with corticosteroid therapy and relapse upon treatment taperKEY

Palabras clave: Cryptogenic organizing pneumonia, intraalveolar fibrosis, butterfly pattern, bronchiolitis obliterans organizing pneumonia, alveolar wall, Masson bodies