Fearing a potential leak from a segment of diverticulitis into the peritoneum, radiologists often use gastrografin, hypaque, or a water soluble dye that can go almost anywhere and still be excreted by the kidneys Using contrast helps expose rectosigmoid tics as well as severe discomfort and spasm, but it is the development of small tracts of contrast, sinus tracts, that help make the diagnosis of diverticulitis. However abscesses and how they may relate to other parts of the bowel, are not visible. For that, a CT scan is needed. In the last several years, CT has become generally the test of choice. There is quite a bit of controversy with CT as to the use of contrast agents.
Some radiologists use all sorts of intravenous, oral or even rectal contrast agents.
In the normal patient with no disease of the large bowel, the rectosigmoid is seen as a clean tube in the lower pelvis ultimately hooking up with the end of the tube, the rectum. If there is contrast in the lumen, the sigmoid has the appearance of a clean thin-walled tube surrounded by varying amounts of fat that appears black on CT images. The radiologists can often see the diverticuli themselves. If there is diverticulitis in addition to tics, imaging will show a narrowed tube with thick irregular walls and smudging of the fat that surrounds the infection. Making this even more confusing is the fact that the two conditions can occur together, such as in patients who have undetected cancer of the rectosigmoid that has perforated and become inflamed or in those patients who develop cancer in an area of their large bowel that is prone to chronic diverticulitis.