A sessile serrated adenoma, also known as a sessile serrated polyp, is a type of growth that develops on the inner lining of the colon or rectum. These are one of several kinds of polyps that can form in the large intestine. Unlike other polyps that may grow on a stalk, these growths are attached to the intestinal wall with a broad base.
These polyps are asymptomatic and are found during routine colonoscopy screenings. Their formal classification by organizations like the World Health Organization reflects an increased awareness of their distinct nature compared to other polyps. This recognition helps in differentiating them and understanding their specific characteristics.
Characteristics and Detection
The term “sessile” indicates that the polyp is flat and broad-based, growing directly on the surface of the colon’s lining. This is in contrast to pedunculated polyps, which are attached to the colon wall by a stalk. This flat morphology can make SSAs blend in with the surrounding tissue, presenting a challenge for detection.
The word “serrated” refers to the saw-toothed appearance of the polyp’s cells when viewed under a microscope. This microscopic pattern is a defining feature that pathologists look for to distinguish SSAs from other types of polyps. The serrated look comes from the specific way the cellular crypts, or glands, in the polyp are structured.
These characteristics make SSAs subtle and difficult to identify during a standard colonoscopy. They are often pale, covered by a thin layer of mucus, and have indistinct borders. Because they are frequently located in the right side of the colon, their detection requires a meticulous examination. Advanced imaging techniques, such as narrow-band imaging (NBI), can enhance the visibility of these polyps by highlighting surface patterns and blood vessels.
Cancer Risk and Progression
Sessile serrated adenomas are considered precancerous, meaning they possess the potential to develop into colorectal cancer over time if left untreated. It is estimated that between 20% and 30% of all colorectal cancers originate from serrated polyps.
The progression of SSAs to cancer occurs through a distinct molecular process known as the “serrated pathway.” This pathway differs from the more commonly understood adenoma-to-carcinoma sequence associated with traditional adenomas. The serrated pathway often involves a specific genetic mutation in a gene called BRAF, combined with a process called CpG island hypermethylation, which can lead to cancer more rapidly.
While the majority of these polyps will not become cancerous, certain features increase the risk. The presence of dysplasia, which is the appearance of abnormal cells within the polyp, is an indicator of higher risk. Polyps that are larger, 10 millimeters or more, are also associated with a greater likelihood of progressing to cancer. The risk of these polyps contributing to “interval cancers,” which are cancers diagnosed between scheduled screenings, underscores the importance of their complete removal.
Associated Risk Factors
Several factors, similar to those for other colorectal polyps, are associated with an increased likelihood of developing sessile serrated adenomas. Age is a factor, with the incidence increasing in older adults, particularly those over 50. Lifestyle choices also play a role, as cigarette smoking and obesity are established risk factors.
Some research suggests a connection between heavy consumption of red meat and an increased risk. A family history of colorectal cancer or polyps may also elevate an individual’s risk. In some cases, the presence of multiple serrated polyps can be indicative of a condition known as serrated polyposis syndrome, which carries a substantially higher risk of developing colorectal cancer.
Removal and Surveillance
The standard approach for managing sessile serrated adenomas is their complete removal at the time of detection during a colonoscopy. This procedure, known as a polypectomy, is performed by the endoscopist using specialized tools. For smaller polyps, forceps may be used, while larger or flatter polyps are removed using a wire loop called a snare. The goal is to ensure no polyp tissue is left behind, as incomplete removal can lead to recurrence.
After the removal of an SSA, a follow-up plan for surveillance is established. Because these polyps can be difficult to detect, individuals who have them removed are advised to have more frequent colonoscopies. The recommended interval for the next screening is shorter than for individuals with no polyps or less concerning types of polyps.
The specific surveillance timeline depends on several factors, including the size and number of the polyps removed, and whether dysplasia was present. For example, the presence of a large SSA (10mm or greater) or one with dysplasia often leads to a recommendation for a follow-up colonoscopy in about three years.