Radiographs and CT scans.—A mass is any pulmonary, pleural, or mediastinal lesion seen on chest radiographs as an opacity greater than 3 cm in diameter (without regard to contour, border, or density characteristics). Mass usually implies a solid or partly solid opacity. CT allows more exact evaluation of size, location, attenuation, and other features. (See also nodule.) [Fleischner Society]
In the lung, mass is defined as greater than 30mm in size.