Focal colonic thickening on CT is common and has multiple causes. Focal thickening involves a short segment of the colon. The thickening may or may not be accompanied by inflammation in the surrounding tissues. The finding is often subjective. Meaning the radiologist determines this based on his experience.
Thickening of a focal segment may not necessarily be from an abnormality. Many CTs will show areas of the colon which look thickened. This may simply be from the colon propelling contents or peristalsis. Other areas are poorly distended and appear thickened. If the CT is done without oral contrast, thickening may be over diagnosed. The bowel may not be well evaluated without oral contrast.
Focal thickening may represent an inflammatory disorder. This can be a colitis from various causes, although this involves longer segments in my experience. Strictures which is narrowing of the colon can occur and cause focal thickening. Strictures can be from prior inflammation or cancer.
It is important to remember that the best test for the colon is a colonoscopy which is a direct look inside the colon. A flexible tube with a camera is passed through the anus to look directly in the colon. CT is not a very good test to evaluate the colon. Nevertheless, abnormalities are sometimes discovered.
CT is good at diagnosing colitis, but not so good at detecting colon cancer. CT often shows areas of focal thickening for various reasons which are not abnormal. So it is possible that an abnormality will be called when there is non. The opposite is also true. An abnormality which may be cancer can be overlooked and attributed to normal physiology.
Some additional findings which help the radiologist when they see focal thickening of the colon is inflammation in the surrounding tissues. Often inflammation in the surrounding tissues indicates that the focal thickening of the colon is abnormal, and commonly because of diverticulitis.
Seeing abnormal lymph nodes adjacent to focal thickening of the colon raises suspicion for colon cancer. Any other evidence of cancer spread, such as that to the liver also raises suspicion. Often, we get patients to CT for staging after a mass is found on colonoscopy. In these cases, the colonoscopy report will tell us where the mass is. It’s easier to find a colon abnormality if we know where to look.
Focal thickening of the colon on CT is therefore a non specific finding which can be normal physiology or from inflammatory causes and cancer. There are additional findings and clinical history which can help with the diagnosis. Ultimately, a colonoscopy may be needed to determine if the finding is abnormal. Further CT testing with oral contrast may also be helpful.