CTICasesSarcoidosis with the Fairy Ring Sign
Imaging findings
CT in a 53-year-old with cough shows numerous nodules with an upper lung predominance, clustering along the bronchovascular bundles and adjacent to veins. One area forms a reverse halo or atoll configuration, but the denser rim consists of discrete tiny nodules rather than smooth consolidation. Mediastinal and peribronchial lymph nodes are present, and a second, less well-defined ring is seen in the upper lung.
Key takeaways
When the rim of a reverse halo is made of tiny nodules rather than a smooth band of consolidation, the appearance is called the fairy ring sign and points to a granulomatous process — most often sarcoidosis. The distinction from a conventional reverse halo matters because the nodular rim is what implies granulomas. The name comes from the circular rings of toadstools that appear in grass after warm, heavy rain.
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