Sessile serrated adenoma of the colon and rectum

by David Driman, MBChB FRCPC
May 16, 2023

What is a sessile serrated adenoma?

A sessile serrated adenoma (SSA) is a non-cancerous growth in the colon. SSA is considered a precancerous condition because it can change into a type of colon cancer called adenocarcinoma over time. For this reason, all SSAs should be removed completely.

Where are sessile serrated adenomas normally found?

Sessile serrated adenomas are most often found on the right side of the colon, including parts of the colon that are designated as the cecum, ascending, and transverse colon, but they may occur in any location including the rectum.

Does sessile serrated adenoma mean cancer?

No, SSA does not mean cancer. However, all SSAs are considered precancerous growths because they can turn into a type of colon cancer called adenocarcinoma over time.

What is the difference between a sessile serrated adenoma and a polyp?

In pathology, the term polyp is used to describe any growth that sticks out from the surface of a tissue. Because of the way they grow, SSAs are a type of polyp. However, not all polyps in the colon are SSAs. Other types of polyps in the colon and rectum include tubular adenomas, tubulovillous adenomas,  villous adenomas, hyperplastic polyps, and traditional serrated adenomas.

How is the diagnosis of sessile serrated adenoma made?

The diagnosis of SSA is usually made after the adenoma is removed during a medical procedure called a colonoscopy. The adenoma may be removed in one piece or in multiple pieces. The tissue sample is then sent to a pathologist for examination.

Unfortunately, it is possible for gastroenterologists and surgeons to miss SSAs when doing a colonoscopy as they can be very difficult to see. They can be flat and indistinct and may blend in with the surrounding lining of the colon.

What is a sessile serrated adenoma with dysplasia and why is dysplasia important?

Colon cancer can start in a sessile serrated adenoma. When cancer develops in an SSA, it usually starts in an area of abnormal growth called dysplasia. For this reason, all SSAs are examined carefully for any signs of dysplasia. Some pathologists divide dysplasia in an SSA into low and high grades, however, this is not currently recommended.

All SSAs require complete removal at colonoscopy but the presence of dysplasia may require a quicker repeat colonoscopy if the removal wasn’t complete on the first visit.

What is a margin?

A margin in an adenoma is the part of the colon or rectum that the gastroenterologist or surgeon cuts to remove the abnormal tissue. Pathologists do not usually state in their report whether the SSA has been completely removed or not, as this is thought to be best judged by the physician doing the colonoscopy.

SSAs are often removed and sent to pathology as multiple pieces (fragments) of tissue. In some of these cases, it will not be possible for your pathologist to determine which piece is the real margin and the changes seen at the margin will not be described in your report.

If there is cancer within the SSA, the pathology report must indicate the distance of the cancer from the margin (the point at which the adenoma was attached to the colon).