Sessile serrated adenoma of the colon and rectum

by David Driman, MBChB FRCPC
April 18, 2022

What is a sessile serrated adenoma?

A sessile serrated adenoma (SSA) is a non-cancerous growth in the colon. However, it can become cancerous if left untreated or not completely removed. An SSA is a relatively new type of polyp, having only been recognized for the past two decades. Before this, most of these polyps were called hyperplastic polyps, although we know now that they are in fact different. Hyperplastic polyps still occur and are common, but they tend to be found on the left side of the colon, as opposed to the right-sided location of most SSA.

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.

How do pathologists make the diagnosis of sessile serrated adenoma?

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.

A sessile serrated adenoma examined under the microscope

What does dysplasia mean and why is it important?

Colon cancer can start in a sessile serrated adenoma. When cancer develops in an SSA, it usually starts in a pre-cancerous condition called dysplasia.

Dysplasia is a word pathologists use to describe an abnormal pattern of growth. In the colon, dysplasia can be either low grade or high grade, depending on how abnormal it looks to a pathologist when viewed under the microscope. High-grade dysplasia is more closely related to cancer than low-grade dysplasia.

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.

Sessile serrated adenomas 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).