The Reversed Halo Sign: Not Such a Specific Sign of Organising Pneumonia

The reversed halo sign is defined as a focal rounded area of ground-glass opacity surrounded by a more or less complete ring of consolidation. It is a relatively rare sign and initially considered a specific sign of organising pneumonia. We report the case of a 55-year-old female who was being followed-up in a pulmonology consultation due to a 6 mm nodule which required vigilance. On a re-evaluation chest CT scan, besides a stable 6 mm nodule, a 36 mm mass with the reversed halo sign was diagnosed. The presence of the reversed halo sign misled the multidisciplinary team into the diagnosis of organising pneumonia and initiation of corticotherapy was suggested. However, after further investigation, a final diagnosis of pulmonary tuberculosis was made. Even though this sign is relatively rare, and still considered an important clue to the diagnosis of organising pneumonia in immunocompetent patients, other causes must be excluded before starting treatment. LEARNING POINTS: The reversed halo sign (RHS) is defined as a focal rounded area of ground-glass opacity surrounded by a more or less complete ring of consolidation. It is a relatively rare sign, and still considered an important clue to the diagnosis of organising pneumonia (OP). However, the RHS has been described in other pulmonary diseases. The diagnosis of OP depends upon the demonstration of typical histopathologic features, usually through lung biopsy, and exclusion of other diseases which led, in our case, to a final diagnosis of pulmonary tuberculosis.