Which flexure of the colon is best demonstrated in the right posterior oblique position during a lower gastrointestinal tract contrast media exam?

The correct choice is the splenic flexure, which is best visualized in the right posterior oblique position during a lower gastrointestinal tract contrast study. In this position, the combined effects of gravity and the orientation of the colon allow for optimal visualization of the splenic flexure, which is the area where the transverse colon transitions into the descending colon, located on the left side of the abdomen.

When the patient is in a right posterior oblique position, it helps in minimizing superimposition of other structures and enhances the contrast medium's delineation of the splenic flexure. This positioning is particularly advantageous as it provides a clearer view by opening up the area between the colon segments and reducing overlapping anatomy, facilitating assessment for any abnormalities.

In contrast, other flexures such as the hepatic flexure are more prominent on the right side and might not be as distinctly visualized in this positioning, making the splenic flexure the focus of clarity in a right posterior oblique position.