The popularization of computed tomography (CT) in clinical practice and the introduction of mass screening for early lung cancer with the use of CT have increased the frequency of findings of subtle nodules or nodular ground-glass opacity. Nodular ground-glass opacity may be observed in malignancies such as bronchioloalveolar carcinoma and adenocarcinoma, as well as in their putative precursors, such as atypical adenomatous hyperplasia. Nodular ground-glass opacity also may be seen in the presence of benign conditions, including focal interstitial fibrosis, inflammation, and hemorrhage. The persistence of nodular ground-glass opacity over time may be strongly suggestive of an early-stage malignancy, especially if the lesion increases in size or includes a solid component that increases in its extent. Persistent nodular ground-glass opacity also may remain stable in size but show increased attenuation. The more extensive the solid portions of the lesion, the higher the probability of malignancy and the poorer the prognosis. An awareness of the clinical setting, in addition to familiarity with the thin-section CT features of nodular ground-glass opacity at initial and follow-up imaging over several months, can help identify malignancy and achieve an accurate diagnosis. A meticulous evaluation of those CT features, and their correlation with specific histopathologic characteristics, also may enable a more accurate prognosis in cases of neoplastic disease.
(c) RSNA, 2007.