The ground glass halo around a nodule suggests the involvement of the adjacent alveoli or septa at a resolution too fine for our CT equipment. It could represent either fluid/hemorrhage or possible "lepidic" growth of a tumor (i.e. adenocarcinoma in situ).

A pulmonary metastasis may be surrounded by a peritumoral hemorrhage and result in a ground glass nodule. Certain metastases do this more commonly, such as:

• melanoma
• renal cell carcinoma
• choriocarcinoma
• angiosarcoma

However, the ground glass nodule is not a specific finding, and in the setting of an oncologic patient, who may be immunocompromised from chemotherapy, it is prudent to suggest a differential that includes infectious processes that have ground glass halos, such as:

• angioinvasive aspergillosis
• candidiasis
• possibly, tuberculoma

Lymphoma and a lymphoproliferative process may also present with ground glass nodules/masses, another consideration in an immunocompromised patient.

Gastrointestinal adenocarcinoma metastases have been shown to have a lepidic pattern of growth. They may uncommonly present with a ground glass halo (~3%).