Serrated polyposis is a condition involving the presence of multiple distinctive growths, known as serrated polyps, within the colon or rectum. These polyps are characterized by a unique sawtooth-like pattern when viewed under a microscope. Understanding serrated polyposis is gaining recognition as an important aspect of colon health.
Understanding Serrated Polyps
Serrated polyps represent a diverse group of growths. The main types include hyperplastic polyps (HPs), sessile serrated lesions (SSLs), and traditional serrated adenomas (TSAs). HPs are the most common, making up approximately 75% of serrated polyps. They are typically small, often less than 5 millimeters, and are usually found in the lower colon and rectum. HPs are considered harmless and do not typically develop into cancer.
Sessile serrated lesions (SSLs) are larger and often located in the upper colon. These polyps are challenging to detect during colonoscopy because they tend to be flat or slightly raised, blend in with the surrounding tissue, and may have indistinct borders or a mucus cap. SSLs are considered precancerous and carry a higher risk of developing into colorectal cancer compared to hyperplastic polyps.
Traditional serrated adenomas (TSAs) are the least common type, accounting for less than 1%. They can be flat or mushroom-shaped and are often found in the left side of the colon and rectum. Like SSLs, TSAs are also considered precancerous and have the potential to become malignant.
How Serrated Polyps are Detected
Serrated polyps do not cause noticeable symptoms, so they are often found during routine colorectal cancer screenings. Colonoscopy is the primary detection method. During a colonoscopy, a flexible tube with a camera is inserted into the rectum to visualize the large intestine. This allows identification and removal of abnormal tissue, including polyps, for examination.
The subtle appearance of many serrated polyps, particularly hyperplastic polyps and sessile serrated lesions, can make them challenging to detect due to their small, flat nature. Newer colonoscopes with higher resolution and magnification improve detection rates. Techniques like chromoendoscopy (using a dye to enhance visibility) and a slower colonoscope withdrawal time also aid detection. Stool tests, such as the fecal immunochemical test, can indicate blood in stool but are not ideal for detecting serrated polyps, as these polyps often do not bleed significantly.
The Connection to Colorectal Cancer
Serrated polyps, especially SSLs and TSAs, are recognized as precursors to colorectal cancer. These polyps can evolve into cancer through a distinct process, the “serrated pathway” of carcinogenesis. This pathway differs from the more commonly understood adenoma-carcinoma pathway, which involves conventional adenomas. Approximately 15% to 30% of colorectal cancers are believed to arise from serrated polyps via this pathway.
The serrated pathway often begins with genetic and epigenetic changes, such as BRAF or KRAS gene mutations and altered DNA methylation patterns. BRAF mutations are frequently associated with SSLs, especially those in the right colon. Accumulated changes can lead to a serrated polyp progressing into an advanced lesion and eventually colorectal cancer. While not all serrated polyps become cancerous, the presence of SSLs and TSAs signals a notable risk for future cancer.
Management and Ongoing Care
Management of serrated polyps involves their removal during a colonoscopy, known as endoscopic polypectomy. Complete removal of the polyp aims to prevent cancer progression. For larger lesions, especially those over 10 mm, cold snare piecemeal endoscopic mucosal resection is becoming the standard approach. This technique allows for safe and effective removal of larger polyps.
Following polyp removal, ongoing surveillance through repeat colonoscopies is recommended. Frequency is determined by the type, size, and number of serrated polyps found. For example, if an SSL 10 mm or larger, or one with dysplasia, or a TSA is detected and removed, a follow-up colonoscopy is generally recommended in three years. Patients with serrated polyposis syndrome (numerous or large serrated polyps) typically require more frequent surveillance, often every one to two years once larger lesions are cleared. Adherence to these schedules is important for early detection of new or recurring polyps, helping prevent colorectal cancer.