Polyps are growths on the inner lining of the large intestine. While many are harmless, some types can develop into colorectal cancer. Understanding these different types, especially sessile serrated polyps (SSPs), is important for colon health and cancer prevention. Recognizing their unique characteristics and potential for progression allows for appropriate screening and timely medical intervention.
What Are Sessile Serrated Polyps/Adenomas?
Sessile serrated polyps (SSPs), also known as sessile serrated adenomas (SSAs) or sessile serrated lesions (SSLs), are a distinct type of growth found in the colon. “Sessile” describes their flat or slightly elevated appearance, meaning they do not have a stalk, which can make them subtle and challenging to spot during a colonoscopy. These polyps are predominantly found in the right side of the colon, such as the cecum and ascending colon.
Under a microscope, SSPs have a characteristic “saw-toothed” or serrated appearance due to the unique folding of the crypt epithelium, which are the glandular structures lining the colon. Their microscopic features include dilated crypt bases and crypts that grow horizontally along the basement membrane, sometimes resembling an “L” or “T” shape. This differs from hyperplastic polyps, which also have serrations but typically show them only in the upper portion of the crypts and have a proliferative zone confined to the lower third.
SSPs are distinct from conventional adenomas (e.g., tubular or villous adenomas), which are characterized by cellular changes known as dysplasia. While SSPs can sometimes show dysplasia, they do not typically exhibit these nuclear changes unless dysplasia is present. The World Health Organization (WHO) now often refers to them as sessile serrated lesions (SSLs) to encompass those that may not yet show dysplasia.
Why Sessile Serrated Polyps/Adenomas Matter
SSPs are precancerous lesions with the potential to develop into colorectal cancer. Estimates suggest that 15% to 30% of colorectal cancers arise through the “serrated pathway.” This pathway differs from the more commonly known adenoma-carcinoma pathway, which involves mutations in genes like APC.
The development of cancer through the serrated pathway is associated with specific molecular changes. These include BRAF gene mutations (e.g., BRAF V600E) and CpG island methylator phenotype (CIMP). CIMP involves the abnormal addition of methyl groups to DNA, which can silence tumor suppressor genes. This combination of BRAF mutations and CIMP is a common feature of SSPs and contributes to their malignant potential.
The presence of dysplasia within an SSL indicates a more advanced stage and a higher likelihood of progressing to invasive cancer. Identifying and removing these polyps is important for preventing colorectal cancer. SSPs also contribute to “interval cancers,” which are cancers detected between recommended colonoscopy screenings.
Finding and Managing Sessile Serrated Polyps/Adenomas
Detecting SSPs during a colonoscopy can be challenging due to their subtle characteristics. These polyps often appear flat, slightly elevated, or may be covered by mucus, making them difficult to distinguish from the surrounding healthy tissue. Their subtle appearance means they can sometimes go undetected even with careful examination.
Successful identification of SSPs relies on high-quality colonoscopy procedures, meticulous technique, and advanced imaging technologies. Newer colonoscopes with higher resolution and magnification capabilities can enhance visibility. Factors such as adequate bowel preparation and the endoscopist’s experience and training also play a significant role in improving detection rates.
Once an SSP is identified, standard management involves complete endoscopic removal, often during the same colonoscopy. For larger lesions, a technique called cold snare piecemeal endoscopic mucosal resection may be used to ensure complete removal. The removed tissue is then sent to a pathologist for microscopic examination to confirm the diagnosis and check for any signs of dysplasia.
Following SSP removal, specific surveillance guidelines are recommended to monitor for new polyps or recurrence, as individuals with these polyps have an increased risk of future colorectal cancer. Follow-up colonoscopy intervals vary based on the polyp’s size, number, location, and presence of dysplasia. For instance, individuals with one or two SSPs smaller than 10 mm without dysplasia may have a repeat colonoscopy in 5 to 10 years. However, if an SSP is 10 mm or larger, or has dysplasia, a shorter surveillance interval, often around 3 years, is recommended.
Serrated polyposis syndrome (SPS) is a rare condition characterized by multiple or large serrated polyps throughout the colon. Individuals with SPS face a higher risk of colorectal cancer and require more frequent surveillance, often with colonoscopies every 1 to 2 years once larger lesions are cleared. First-degree relatives of individuals with SPS are advised to begin screening earlier, around age 40, and undergo colonoscopies every 5 years.