Atoll sign ieventail diagnostic

Abstract

The atoll sign or inverted halot sign is seen on high-resolution chest CT scans as a central frosted glass area surrounded by peripheral condensation in a ring or crescent, the contours of which may be smooth or spiculated [1]. Histologically, the central zone (ground glass opacity) corresponds to alveolar septal inflammation and cellular debris in the alveolar spaces, while the condensed peripheral zone corresponds to granulomatous tissue in the distal air spaces [2]