During an air-contrast barium enema, which position best demonstrates the right colic flexure?

The left posterior oblique position is the best choice for demonstrating the right colic flexure during an air-contrast barium enema because this positioning utilizes the natural gravitation effect of the barium contrast. When the patient is positioned in the left posterior oblique orientation, the right colic flexure is rotated and elevated away from the descending colon, allowing for clearer visualization. This oblique position provides optimal contrast between the barium-filled colonic structures and any air that may be present, enhancing the ability to identify the right colic flexure during the examination.

In addition, this positioning also helps to separate the right colic flexure from other adjacent structures, reducing superimposition which might occur when using other positions. Other positions, such as the supine or upright positions, would not provide the same level of access and clarity to the right colic flexure as the left posterior oblique does.