At the time cancer is detected at one site in colon, polyps may be detected at other sites in the same colon. In general, a colon that is predisposed to developing polyps is also predisposed to development of cancer of the colon. Having said all this, there are other common types of polyps in the colon e.g. hyperplastic type. These hyperplastic polyps although very common do not increase the risk for colon cancer. It also follows from this discussion that the patients with colon adenomas may need regular follow-up colonoscopic exams for surveillance while those with hyperplastic polyps do not.
Barium enema involves an x ray of colon after putting barium into the colon.
On the other hand, colonoscopy is direct visualization of the inside lining of the wall of the colon. To equate these two tests is like saying a shadow of an object is equally good as seeing the actual object. In contrast to barium enema, colonoscopy also allows for an opportunity to execute diagnostic maneuvers like taking biopsy as well as perform therapeutic modalities like removal of polyps. Most endoscopies are performed under conscious sedation and are well tolerated. During such state, the patient is responsive but sedated and breaths on his own.