Cryptogenic organizing pneumonia

There are areas of clearing consolidation with central ground glass, also known as the reverse halo sign. Instead of ground glass surrounding an opacity/nodule ("halo sign"), there is an opacity/consolidation with a central ground glass density ("reverse halo").

There is the so called "atoll sign". As the consolidation clears away from the peripheries, the resultant curvilinear band of atelectasis is akin to an atoll.