Reversed halo sign: a systematic review.

A reversed halo sign (RHS) is defined as the presence of a focal ring-shaped area of ground-glass opacity within a peripheral rim of consolidation. Although originally described in patients with cryptogenic organizing pneumonia, it has been described with several other noninfectious and infectious diseases, including fungal infections. Thus, it is imperative that a proper diagnosis be established before initiating treatment. In this article, we systematically review the literature (PubMed and Embase) for the associations of the RHS. We have also proposed a diagnostic algorithm for an approach to a patient with an RHS.