The Reversed Halo Sign: Another Atypical Manifestation of Sarcoidosis

Abstract

We read with great interest the well-written and informative pictorial essay by Park et al. (1), which reviews the thoracic manifestations of sarcoidosis, classifying them as typical and atypical. They indicate that the less frequent and unusual manifestations may be observed in 25% to 30% of cases, emphasizing the difficulty to differentiate sarcoidosis from other diseases, and the importance of understanding the radiological manifestations of sarcoidosis in making a proper diagnosis. We would like to add another atypical aspect of the disease, recently reported by Kumazoe et al. (2) and also observed by us, which is the reversed halo sign (RHS). The RHS is defined as a focal, rounded area of groundglass surrounded by an approximately complete ring of consolidation. This sign was described by Kim et al. (3) as a finding that was relatively specific to making a diagnosis for cryptogenic organizing pneumonia (COP). Later, various authors demonstrated the presence of this sign in a wide spectrum of diseases (4), including infectious (paracoccidioidomycosis, tuberculosis, zygomycosis, and aspergillosis, among others) and non-infectious conditions (Wegener’s granulomatosis, lymphomatoid granulomatosis, and bronchioloalveolar carcinoma, among other processes). Therefore, the RHS must be regarded as a nonspecific sign that is encountered in various pulmonary diseases. Also, it may correspond to secondary organizing pneumonia in numerous conditions, as a response to the primary disease. In the case reported by Kumazoe et al. (2), the high resolution CT (HRCT) images showed multiple central ground-glass opacities surrounded by crescent or ringshaped areas of consolidation in both lungs (RHS). Moreover, the authors observed miliary nodules in the Letter to the Editor