Can a ct scan see a tumor or mass inside the colon???

Not the best test: Possibly a CT or "virtual colonscopy" (a type of CT scan) would detect a mass in the colon, but the very best by far is a colonoscopy. Another advantage is if there is a polyp (that may be pre-cancerous), it can be removed during the colonoscopy procedure. The prep (drinking liquid to clean out the colon) prior to the colonoscopy is normally worst part, and this has gotten much easier of late.