Ground-glass opacity (GGO) is defined as an opacity that does not obscure underlying bronchial structures or pulmonary vessels at high-resolution computed tomography (CT). 
GGO is a rather unspecific radiologic feature seen in a number of clinical conditions involving different pathologic processes. 
GGO on images may represent partial alveolar filling or could be due to interstitial changes. 
Nodular sub-solid densities may be caused by several infectious or inflammatory entities, however most will resolve on short-term follow-up study. Persistent nodular sub-solid density is a well known appearance of primary lung adenocarcinoma and are frequently managed by surgical resection. However, not all are cancer or premalignant lesions, therefore, familiarity with other differential diagnosis is important in patient standard of care. These include lymphoproliferative disorders, IgG4-related diseases, and scar.
In this educational exhibit we review the histopathology and the radiological findings of the above-mentioned causes of non-adenocarcinoma ground glass nodules.

Persistent Pulmonary Sub-solid Nodular Densities, Not In the Spectrum of Adenocarcinoma.