Would colorectal cancer show up in pelvic ct scan ?

Rarely: The cancer would have to be quite large to show up on a pelvic ct scan. A colonoscopy is a much better test for colorectal cancer. Some centers are using a special kind of ct scan called "ct colonography" to dected colorectal cancer.

Yes, when it is big: It can be shown up in a ct scan when the size is large enough and by then the chance is probably it is already giving you symptoms like abdominal pain/cramping , change in bowel movement, etc. Small polyps or small tumor in colon would not be able to be picked up on ct scan and colonosocpy is the best modality to screen for colon cancer.

Not necessarily: Colon extends far outside the pelvic area and considerable parts of the colon would not be subject to imaging in a pelvic ct. Presence of feces in the colon also limits the ability of ct examination to detect colon cancer.

Can: But not always. Colonoscopy best.

Maybe: Sometimes - it needs to be big enough to be seen. Early colon cancer, which is when we want to find and treat it may not be seen on any imaging.