"Reversed halo sign".

Appearance: The reversed halo sign (also known as the atoll sign, reverse halo sign, and the fairy ring sign) is defined by central ground-glass opacity with a surrounding halo or crescent of consolidation (Fig. 1). This should not be confused with the halo sign which refers to central consolidation with a surrounding halo or rim of ground-glass opacity. Furthermore, the reversed halo sign should be differentiated from cavitation (development of focal regions of internal gas) or pseudocavitation (likely internal bronchiolectasis described in subtypes of lung adenocarcinoma).