Why Is Oral contrast Needed for CT?

Oral contrast is given as a drink before a CT scan to highlight the bowel.   Often there is a 1-2 hour wait before scanning takes place to allow enough time for the contrast to highlight the bowel.   The bowel which includes the small intestine and colon occupies a large amount of space in the abdomen and pelvis.  Highlighting the bowel with oral contrast makes it easier for the radiologist to read the scan and provide the most accurate diagnosis.

The bowel without oral contrast can hide abnormalities on the CT or even look like an abnormality.   Bowel loops can bunch together and cause an appearance of an abnormal mass in the abdomen.  Bowel loops can make an organ look abnormal.  An example would be when bowel is next to the pancreas and makes it look like there is a mass.  Bowel loops can also hide abnormalities by covering or hiding them, especially when they bunch together.

Abnormalities of the bowel itself are also better seen when there is oral contrast given.  The wall of the bowel will better be seen when the inside of a bowel loop is highlighted with oral contrast.  The bowel wall is important to assess for important abnormalities such as inflammation, tumor or lack of blood flow.  The wall of the bowel will often be thickened in these cases.

An obstructed bowel is also more easily diagnosed when oral contrast is given.  The oral contrast will move slowly through the bowel when it is obstructed or blocked.  The oral contrast may also highlight the cause of the obstruction or blockage.  Oral contrast will also better show abnormalities inside or next to bowel in some cases.  Like a mass inside the bowel or coming off the wall.  Oral contrast will often distend the bowel loops more allowing abnormalities to be better seen.

Oral contrast is helpful when imaging a thin patient who does not have much fat to spread structures apart.  Not giving oral contrast in these patients may make it difficult to see organs and abnormalities because everything is bunched together.  Highlighting the bowel will allow everything else including abnormalities to stand out.

Giving oral contrast can also be helpful in cases where appendicitis is suspected.  Sometimes the appendix is tough to see.  Other times, the appearance is borderline abnormal.  Giving oral contrast can be helpful to find the appendix.  It can also help in borderline cases, especially when the appendix is highlighted by the oral contrast.

A CT with oral contrast takes more time to do but can be very helpful.  It often makes it easier for the radiologist to read the scan and provide the most accurate diagnosis.  Oral contrast can make it easier to see abnormalities of the bowel or any structures next to it.  Oral contrast can be very helpful in some cases of suspected appendicitis.   Oral contrast can sometimes hide abnormalities.  A few examples would be if your looking for something bright like a kidney stone in the ureter or a bleed.  But these diagnosis are often made in the presence of oral contrast as well.