Psittacosis with a reversed halo sign

A 26 yr old woman^† presented to the emergency room of Juntendo University Hospital, Tokyo, Japan, in June 2016 with a two-week history of cough and fever after coming into contact with pigeon faeces. She was admitted and serologically diagnosed with psittacosis. Chest radiography revealed a uniform infiltrative shadowing in the left upper lung field (Fig. 1), and chest computed tomography (CT) revealed a bronchial wall thickening, air-space consolidation and a reversed halo sign, characterized by a denser uniform shadow surrounding the central ground-glass opacity in the periphery of the left upper lobe (Fig. 2). Symptoms promptly improved with three days of oral azithromycin (500 mg/day). Radiography performed 26 days after onset showed no pneumonia, but a mild cough persisted for two months.

Fig. 1: Chest radiograph showing a uniform infiltrative opacity in the left upper lung field (arrows).

Fig. 2: Axial chest computed tomography showing a reversed halo sign along with bronchodilation, bronchial wall thickening, nodular shadowing and air-space consolidation (arrows).

A reversed halo sign on CT is seen in many diseases. The pneumonia lesion of Chlamydia psittaci due to the intense immune reaction spreads non-segmentally through Kohn pores, but the older, central part of the lesion heals quickly. The present picture may represent one of the transient images of the pneumonia.