Ground-glass opacity of the lung parenchyma: a guide to analysis with high-resolution CT.

Ground-glass opacity is a frequent but nonspecific finding on high-resolution CT scans of the lung parenchyma. The underlying abnormality is diverse; any condition that decreases the air content of the lung parenchyma without totally obliterating the alveoli can produce ground-glass opacity. These processes are not visible on high-resolution CT scans. However, in specific clinical settings, the information provided by high-resolution CT is considerable when the anatomic distribution and associated structural changes to the lung parenchyma are analyzed. This pictorial essay illustrates the pathologic basis of ground-glass opacity and provides a guide to the differential diagnosis of the disorders that can produce this appearance.