Linear shadows in the air-contrast barium enema.

In 3 patients with carcinoma of the colon, lesions were seen as linear shadows on air-contrast barium enema studies. When the elevation of a lesion is slight or the tumor--mucosal interface is gently sloping, the tumor's proximal and distal edges may be ill-defined or disappear altogether. Thus only a linear shadow representing the interface between the tumor surface and air in the lumen appears. Other causes of these lines are also discussed.