This case demonstrates how polyps can change their appearance on fluoroscopy depending on the technique used. It's also meant to show the strength and weakness of "pseudo-double contrast" technique ("pseudo-double contrast" instead of "double contrast" because no effervescent agent was administered and because the barium is lower density than that used with double contrast).

On the initial single contrast views the smaller polyp is easier to see given its location and given its shape which sticks out more into the lumen than the larger polyp. On earlier views this polyp was less visible because the stomach was over-filled with contrast, obscuring it (on some of the earliest images (not shown) it's invisible!). As the contrast transits into the duodenum, the greater curvature polyp becomes more visible as the antral contrast pool becomes less dense. When most of the contrast had moved through the stomach, allowing a "pseudo-double contrast" view of retained swallowed air and residual contrast, then the greater curvature polyp became even more visible with almost a "bowler hat" appearance. 

The larger, flatter polyp is, interestingly, harder to see than the smaller polyp. One sees it better in profile on the single contrast images, but when the stomach rotates into a different plane, bringing the polyp en face on the dependent surface, then it becomes very difficult to see with either technique.