Intestinal polyp counting

Overview

This is the protocol we use to count intestinal polyps. To determine the anatomical sections of the small intestine from the stomach to the cecum, the 1st 5% of the small intestine is the duodenum, the next 45% is the jejunum, and the remaining 50% is the ileum. In our SB screens, the proximal jejunum normally has the most tumors, and the distal jejunum differs anatomically from the proximal jejunum. There is a noticeable difference in the heighth and width of the villi, with the largest villi located in the duodenum and jejunum, and significantly smaller sized villi in the ileum.

Protocol

Lay the intestines with the villi facing upwards in a flat petri dish containing a small amount of 70% ethanol. View the intestines using a high quality stereo microscope, ideally with a reticle in the eyepiece for measuring the diameter of the polyp. Start with the duodenum and proceed towards the colon.

Polyps will have a dark structure, and light will not pass through the polyp, like it will pass through villi. Villi have a wheat-like appearance and can be pushed from side to side and light will pass around them. Polyps will be darker and have a more solid structure. In general, polyps will have a floret/crater appearance. The size of the polyp can vary greatly, but the structures are similar. The following are examples of polyps in the intestines.

The following images are examples of small polyps. As long as the polyp is > 0.2 mm it should be counted.

The above "satellite" polyps, however should not be confused with extensive growth from a single polyp, as shown below. The image below is only a single polyp, the structures in the red boxes should not be counted separately.

The following image displays unusual small, dark round polyps that were found in mice that lacked p19ARF or expressed a dominant negative p53. They are still counted as polyps.

The following is an example of a fused polyp, because when grasped with forceps the two structures could not be pulled apart. This should only be counted as a single polyp.

When you encounter a potential polyp, grasp gently with the forceps. If it is a polyp, the forceps will not pass through or squash the structure like it would if you grasped a clump of villi.

The number of polyps can vary considerably in mice with the same genotype. We typically see a variance of up to 30%.

Peyer's patches (intestinal lymph nodes) can be easily confused with polyps. The key differences between a Peyer's patch and a polyp are:

• Patches originate on the outside of the intestines, so there will be a bump on the outside of the intestinal wall, unlike most polyps
• Villi will lie on top of the patches, or at least part of the patches, unlike polyps.
• Patches are blue-grey in color, unlike polyps.

The following are images of Peyer's patches.

Sometimes the intestine will have "lumps" that are not polyps. Although they are abnormal, they are more likely to be a bed of inflammation. Generally these will be more like a hill than a polyp. The following is an image of a lump.