Signs in Thoracic Radiology-For the Radiology Residents

CT angiogram sign-Enhancing braching pulmonary vesseles visualised against a low attenuation lung parenchyma.

The CT angiogram sign was initially described as a specific sign of lobar bronchoalveolar cell carcinoma; specificity can be as high as 92.3%. Recently, the results of several retrospective studies have challenged the specificity of the CT angiogram sign; the CT angiogram sign was reported to be seen in both benign and malignant entities, including bronchoalveolar cell carcinoma, pneumonia, pulmonary edema, obstructive pneumonitis due to central lung tumors, lymphoma, and metastasis from gastrointestinal carcinomas.

An excellent article with image, differentials and findings here-

http://radiologywiki.org/index.php/CT_angiogram_sign