Ground-glass opacity refers to areas on CT scans of the lungs that appear hazy due to increased density of the air spaces. These markings indicate areas of the lungs which are filled, thickened or collapsed, and they help doctors diagnose potential infections, diseases and other problems with the lungs. Ground-glass opacity occurs because the X-ray strength weakens in some areas of the lungs quicker than other areas.
Ground-glass opacity may indicate opportunistic infections, such as pneumocystis pneumonia, cytomegalovirus pneumonia, herpes simplex virus pneumonia and respiratory syncytial virus bronchiolitis; chronic diseases, such as eosinophilic pneumonias, idiopathic interstitial pneumonias and sarcoidosis; and other issues, such as cancers with lepidic proliferation or drug toxicity. Other rare causes include focal interstitial fibrosis, aspergillosis, thoracic endometriosis, traumatic lung injury, poisoning, pulmonary cryptococcus infection, Wegener granulomatosis and Henoch-Schönlein purpura.
Circumscribed areas containing ground-glass opacity are referred to as ground-glass density nodules. These nodules are classified as either solid or subsolid. While these nodules can appear commonly in CT scans, nodules that are solid may indicate a significant risk of cancer. Subsolid nodules are less likely to be cancerous; however, the Radiological Society of North America recommends that subsolid nodules greater than 10 millimeters be surgically removed.