In radiology, ground glass opacity (GGO) is a nonspecific finding on computed tomography scans (CT) consisting of a hazy opacity that does not obscure the underlying bronchial structures or pulmonary vessels, that indicates a partial filling of air spaces in the lungs by exudate or transudate, as well as interstitial thickening or partial collapse of lung alveoli.:95
The differential diagnosis of the many causes of GGO includes pulmonary edema, infections (including severe acute respiratory syndrome coronavirus 2, cytomegalovirus and Pneumocystis jirovecii pneumonia), various noninfectious interstitial lung diseases (such as hypersensitivity pneumonitis, Hamman-Rich syndrome), diffuse alveolar hemorrhage, and cryptogenic organizing pneumonia.
Reversed halo signEdit
A reversed halo sign is a central ground-glass opacity surrounded by denser consolidation. Criteria include that the consolidation should form more than three-fourths of a circle and be at least 2 mm thick. It is suggestive of cryptogenic organizing pneumonia, but is only seen in about 20% of individuals with this condition. It can also be present in lung infarction where the halo consists of hemorrhage, as well as in infectious diseases such as paracoccidioidomycosis, tuberculosis, zygomycosis, and aspergillosis, as well as in granulomatosis with polyangiitis, lymphomatoid granulomatosis, and sarcoidosis.
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