Ground-glass attenuation

Ground-glass opacity is a highly significant finding on HRCT, as it often indicates the presence of an active and potentially treatable process; active disease is present in more than 80% of patients who show this finding. Because of its association with active lung disease, the presence of ground-glass opacity often leads to further diagnostic evaluation, including lung biopsy.

Because ground-glass opacity can reflect the presence of either fibrosis or inflammation, one should be careful to suggest the presence of an active process only when ground-glass opacity is unassociated with HRCT findings of fibrosis. If ground-glass opacity is seen only in lung regions that also show evidence of fibrosis, such as intralobular interstitial thickening, honeycombing or traction bronchiectasis, it is most likely that this finding reflects fibrosis rather than an active process.

A large number of diseases can be associated with ground-glass opacity on HRCT. In many, this reflects the presence of similar histological reactions in the early or active stages of disease, with inflammatory exudates involving the alveolar septa and alveolar spaces, although this pattern can be the result of a variety of pathological processes. In most, the disease is patchy in distribution. The most common causes of ground-glass opacity include usual interstitial pneumonia, nonspecific interstitial pneumonitis, desquamative interstitial pneumonia, hypersensitivity pneumonitis, pulmonary oedema and pulmonary haemorrhage, and pneumonias (particularly pneumocystis carinii pneumonia). Less common causes include alveolar proteinosis, acute interstitial pneumonia or other causes of diffuse alveolar damage or the adult respiratory distress syndrome, respiratory bronchiolitis and early radiation pneumonitis.

RW