Dear OncoLink "Ask The Experts,"
Is it possible to miss a tumor during a colonoscopy exam if it is in the cecum? Where can a tumor be located if it can be felt through the wall of the lower colon but is not present during colon exam?

Timothy C. Hoops, MD is a Clinical Assistant Professor of Medicine in the Gastroenterology Division at the University of Pennsylvania and Director of Gastroenterology at Penn Medicine at Radnor responds:

Tumors in the colon can be missed. We know that there is an expected miss rate, although it is small. Additionally, it is typically the smaller tumors that are missed. That being said, there are several reasons a tumor could be missed in the cecum. It may be that the pre-colonoscopy prep was not good enough. The cecum is the hardest place in the colon to get completely clean making visualization of the area difficult. Second, if the procedure is difficult, it may be that the cecum was never reached but the landmarks seen were mistakenly thought to be the cecum. The cecum is the part of the colon that is furthest point from the entrance of the colonoscope. Obviously, one could miss a tumor in the cecum as it was never actually seen. If the entire colon were visualized, it would be unlikely that a significant tumor, large enough to be palpated through the abdominal wall, would be missed. It may be that what is felt is not in the cecum but rather outside it, such as an ovarian mass or a bladder tumor, etc. If there were concern, a barium enema or another colonoscopy would be helpful.