Measurement of levels
Measuring levels by flexible endoscopy is not accurate. Usually the distance will be shorter than estimated by the endoscopist. It is therefore very important that all lesions measured by colonoscope at a level of <25 cm from the anal verge must be reexamined with a rigid scope to achieve a correct measurement. CT, CT-colography and MRI of the rectum can also be helpful in defining the level of the tumor.
The rectum is the bowel from the dentate line in the anal canal til 15 cm above this as measured with a rigid scope. Malignant tumor with the anal border in this area is defined as a rectal cancer in Norway. (Other definitions are used in other countries, for instance 12/16 cm from the anal verge).
Measurement with a rigid sigmoidoscope:
- Lower rectum. From the dentate line till 6 cm above the anal verge.
- Middle rectum. 7-10 cm above the anal verge.
- Upper rectum. 11-15 cm above the anal verge.
- The peritoneal fold is mostly at 10 cm, which is most often equivalent to Huston’s 2.nd fold seen at endoscopy. The rectosigmoid flexure is the bowel at 16-20 cm above the anal verge. When the lover level of the tumor is within this region it is by definition a cancer of the rectosigmoid flexure.
The sigmoid stretches orally from 21 cm.