reversed halo sign

What is the reversed halo sign or “atoll” sign?

The “reversed halo” sign is characterized by ring-shaped or crescentic peripheral consolidation and central ground glass opacity. The appearance has been likened to an atoll, a ring-shaped coral reef that encompasses a central lagoon, with the peripheral land representing the consolidation and the central body of water representing the ground glass opacity.

It should be noted that the imaging appearance of organizing pneumonia is quite protean and can manifest as multiple or solitary nodules mimicking malignancy, ground glass opacities, or a crazy paving pattern.

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