Opacities in the lungs are seen on a chest radiograph when there is a decrease in the ratio of gas to soft tissue in the lungs, according to Radiopaedia.org. The opacities may represent areas of lung infection or tumors.
Lung opacities may be classified by their patterns, explains Radiopaedia.org. The three common patterns seen are patchy or airspace opacities; linear opacities; and nodular or dot opacities. Airspace or patchy opacities may represent consolidation, atelectasis or mucoid impaction. Consolidation indicates solid or liquid occupying the normally gaseous areas in the lungs and may be due to accumulation of fluid, pus, blood, cells, gastric contents, protein or even fat in the lungs. Atelectasis is an incomplete expansion of the lungs.
Ground-glass opacities may represent opportunistic infections such as with pneumocystis or cytomegalovirus or chronic interstitial disease. Linear opacities indicate an interstitial pattern of lung infection or lung disease. Nodular opacities may signify tuberculosis; metastatic or bronchogenic lung tumor; or acute hypersensitivity pneumonitis depending on the size of the nodules. Nodules less than 2 millimeters in size may indicate miliary tuberculosis, notes Radiopaedia.org. Nodules between 2 and 7 millimeters may represent acute hypersensitivity pneumonitis, whereas nodules between 7 and 30 millimeters tend to be lung granulomas or metastases. Masses more than 30 millimeters are likely primary lung tumors.