The colon, or large intestine, can develop growths on its inner lining called polyps. While many of these common growths are benign, some have the potential to transform into cancer. One specific type of polyp that receives particular attention is the sessile serrated adenoma, which has distinct characteristics and requires a specific management plan after it is found.
What Is a Sessile Serrated Adenoma?
The name “sessile serrated adenoma” describes the growth’s specific features. “Sessile” indicates that the polyp is flat or broad-based, growing directly on the surface of the colon wall rather than hanging from a stalk. This flat profile can make them less conspicuous during a colonoscopy. They are often pale and may be covered by a mucus cap, further camouflaging them.
The term “serrated” refers to the microscopic appearance of the polyp’s glands, which have a jagged, saw-toothed pattern. This is a key distinction from conventional adenomas. This saw-toothed architecture is a result of how the cells grow and arrange themselves within the polyp.
“Adenoma” classifies the growth as a benign tumor from the colon’s glandular tissue that has the potential to become malignant. These polyps are most frequently located in the proximal, or right side, of the colon.
Understanding the Cancer Risk
Sessile serrated adenomas, also called sessile serrated lesions (SSLs), are considered precancerous because they can develop into colorectal cancer. It is estimated that 15% to 30% of all colorectal cancers arise from serrated polyps. The discovery of an SSA does not mean cancer is present, but it does identify a heightened risk that necessitates removal and follow-up.
These polyps are precursors to a specific form of colorectal cancer that develops through a distinct molecular process known as the “serrated pathway.” This is an alternative mechanism of cancer development compared to the more traditional adenoma-to-carcinoma sequence. The serrated pathway is characterized by specific genetic changes, like a mutation in the BRAF gene.
The BRAF mutation is part of a larger molecular signature that includes the CpG island methylator phenotype (CIMP). This involves widespread methylation, a chemical modification of DNA, that can silence tumor-suppressing genes, allowing cells to grow uncontrollably. Cancers that develop through this pathway may progress more rapidly than those from conventional adenomas.
Detection and Removal Procedures
Sessile serrated adenomas are detected during a colonoscopy, a procedure using a flexible tube with a camera to inspect the colon. Identifying them can be a challenge for the endoscopist due to their flat and pale appearance. This makes a high-quality colonoscopy, which involves excellent bowel preparation and a careful examination, important for detection. Newer high-definition colonoscopes and advanced imaging techniques also help improve detection rates.
Once a suspected SSA is identified, the standard course of action is to remove it completely. This procedure, known as a polypectomy, is performed during the colonoscopy. For smaller SSAs, removal may be accomplished using a wire loop called a snare, which can be either “hot” (using an electrical current to cut and cauterize) or “cold” (cutting without heat).
For larger or flatter lesions, a technique called endoscopic mucosal resection (EMR) is often used. EMR involves injecting a solution under the polyp to lift it away from the deeper layers of the colon wall, allowing for a safer and more complete removal. Sometimes, very large polyps must be removed in several pieces.
Surveillance and Long-Term Management
The removal of a sessile serrated adenoma is followed by a long-term surveillance plan to monitor for the development of new polyps. The timing of the next colonoscopy depends on several factors found during the initial procedure. A pathologist’s examination of the removed polyp tissue provides the necessary information to guide these decisions.
Determinants for surveillance intervals include the size of the SSA, the total number of polyps found, and the presence of dysplasia. Dysplasia refers to the presence of more advanced, precancerous cells within the polyp, which indicates a higher risk.
For example, guidelines from gastroenterology societies often recommend a follow-up colonoscopy in 3 years if the removed SSA was large (10 millimeters or greater), if there were multiple SSAs, or if any of the polyps showed dysplasia. For individuals with smaller SSAs (less than 10 millimeters) and no dysplasia, the recommended interval for the next colonoscopy may be longer, such as 5 years.
If a person has a very large polyp removed in pieces, an initial follow-up exam may be scheduled in 6 months to ensure the entire lesion was successfully resected before resuming a standard surveillance schedule. This structured follow-up protocol is designed to manage risk by detecting any new growths at an early stage.