What is an ill defined opacity of the lung?

On high-resolution CT of the lung, ground-glass opacity may represent a spectrum of diseases ranging from isolated interstitial abnormalities to isolated alveolar filling, and frequently represents entities involving both parenchymal compartments [1, 2, 3]. Ground-glass opacity has been described as a potential finding in virtually all neoplastic, infectious, and inflammatory conditions involving the pulmonary parenchyma. Not surprisingly, the specificity of this finding in a given case is limited, and even when it is correlated with the clinical setting, a wide differential diagnosis may be applicable. In many instances, ground-glass opacity is a secondary finding in which associated abnormalities including nodules or masses, interstitial changes, and consolidation contribute to a given diagnosis. Well-known examples include the halo sign of invasive aspergillosis and crazy paving in alveolar proteinosis [4, 5]. Furthermore, anatomic distribution of the ground-glass opacity at a lobular level can be used to suggest a diagnosis [6]. Centrilobular distributions are readily recognized in hypersensitivity pneumonitis and panlobular distributions in Pneumocystis carinii pneumonia [7, 8]. ( maybe you got an HIV )