Ground-Glass Opacities

Ground-glass opacity (GGO) is defined at thin-section CT as abnormally increased lung density in which vascular and bronchial margins remain visible. This contrasts with consolidation in which those margins are obscured. In the setting of diffuse lung disease, GGO may be related to airspace filling, interstitial thickening or both. Pathologic processes manifesting as diffuse GGO have widely varied symptoms according to the etiology. The assessment of diffuse GGO is primarily achieved with HRCT. Helpful features in establishing a differential diagnosis include: chronicity, distribution of opacities and ancillary findings. Differential diagnosis of acute GGO includes infection, alveolar hemorrhage and pulmonary edema. Chronic GGO may be seen in hypersensitivity pneumonitis, organizing pneumonia, acute or chronic eosinophilic pneumonia, pulmonary alveolar proteinosis and desquamative interstitial pneumonia (DIP). GGO is a nonspecific HRCT pattern that should always be interpreted in light of acuity of symptoms, specific clinical presentation and laboratory results.