CT is good at showing the colon but not the best at evaluating abnormalities, particularly inside it like masses. There are many mimics of colon abnormality that are not really abnormal. For example, stool may look like a mass in some cases causing a round abnormality. In some cases, the colon can look narrowed or thickened from simply doing its job of contracting. This can mimic abnormality such as tumor on CT in some cases.
The radiologist interpreting the CT may notice an unusual segment of colon and mention it as a possible abnormality. There are many instances where I have seen this turn out to be nothing. However, it still needs to be evaluated. Colonoscopy would be best as this allows a look inside the colon with a camera. There is usually little to no stool inside because of the preparation. Therefore abnormalities will be detected.
Colonoscopy is however invasive, requires sedation and a difficult bowel preparation. It would be easier in some cases to exclude abnormality by other testing. A repeat CT scan with oral contrast is one way if the original CT was done without it. Oral contrast is given before the CT scan and acts to highlight the bowel. Additionally, the repeat CT would allow another look at the abnormal bowel segment. If the abnormality is causes by stool or normal spasm/function then it would be expected to go away when the repeat is done later.
Even a repeat scan without oral contrast later may be helpful since it will allow another look. A mass or abnormality will be expected to persist. Stool or a normal contraction will be expected to resolve on the repeat scan. A PET scan is another option but not as good. The idea is that a colon tumor will be “hot” on pet scan while stool and normal colon will not. It is likely that some colon tumors may not be hot so a PET scan will only be useful in positive cases.
Your clinical doctor may also evaluate your clinical history to see what is best done next. For example, are you losing weight, having anemia, or other blood test abnormalities. Whether you have a family history or other predisposing conditions. This may indicate as higher risk of cancer and more aggressive measures may be needed.