[A case of cryptogenic organizing pneumonia showing reversed halo sign on computed tomography of the chest].

A 56-year-old female non-smoker complained of general fatigue and pyrexia. Laboratory examination revealed elevation of white blood cells (WBC) 10200/microl and C-reactive protein (CRP) 13.3mg/dl. Chest radiograph showed bilateral patchy and ring-shaped consolidations in both lungs. Chest computed tomography (CT) revealed multiple round ground glass opacities fringed with consolidation, namely the "reversed halo sign". Transbronchial lung biopsy specimens showed polypoid granulation tissue in terminal air spaces, consistent with an organizing pneumonia pattern. Clinical findings suggesting collagen vascular diseases and drug induced lung diseases were not recognized, thus cryptogenic organizing pneumonia (COP) was diagnosed. High dose methylprednisolone therapy improved her condition, and the ring-shaped opacities on chest CT resolved. She relapsed twice during approximately five years after the disease onset. Chest CT at the recurrences revealed subpleural patchy consolidations without formation of the "reversed halo sign". The sign was originally supposed to be specific for cryptogenic organizing pneumonia. However, other diseases like sarcoidosis and paracoccidioidomycosis have been reported to show this sign. The meaning of the "reversed halo sign" should be examined based on the accumulation of more cases.