Colorectal polyps are common growths on the inner lining of the large intestine. While many are harmless, some are precursors to colorectal cancer. The risk associated with a polyp is determined by its cellular makeup and its physical structure, known as its morphology. Understanding the specific characteristics of a sessile polyp is the first step in assessing its risk and determining the appropriate path for prevention and follow-up care.
What Defines a Sessile Polyp
A polyp is an abnormal growth of tissue projecting from the mucosal layer of the colon. These growths are categorized by their shape and how they are attached to the intestinal wall. The term “sessile” describes a polyp that is flat, broad-based, or dome-shaped, meaning it is directly attached to the lining without a stalk.
This flat attachment distinguishes sessile polyps from pedunculated polyps, which have a mushroom-like appearance connected by a narrow stalk. The sessile morphology presents specific challenges because the polyp blends easily with the mucus membrane lining the colon. This makes sessile polyps more difficult to detect during screening and complicates complete removal. Their direct connection to the underlying tissue also means that potential cellular changes are closer to the deeper layers of the colon wall.
Understanding the Malignant Potential
The potential for a sessile polyp to become cancerous is determined by its cellular classification, or histology, rather than its shape alone. Sessile polyps can be benign, precancerous, or, less commonly, already cancerous at the time of detection. The most concerning types fall into the category of neoplastic lesions, which have the potential to progress to cancer.
The two main histological categories relevant to sessile morphology are adenomas and serrated polyps. Conventional adenomas, including tubular, villous, or tubulovillous types, are recognized cancer precursors. Sessile morphology often correlates with a villous component, which carries a higher risk. Villous adenomas, for instance, have a higher rate of progression to cancer compared to tubular adenomas.
A particularly significant precancerous sessile polyp is the sessile serrated adenoma/polyp (SSA/P), also called a sessile serrated lesion (SSL). SSA/Ps are often found in the right side of the colon and follow a different molecular pathway to cancer than conventional adenomas. Although hyperplastic polyps are also serrated and considered low-risk, SSA/Ps are definitively precancerous and contribute to a substantial portion of colorectal cancers.
The overall cancer risk is primarily influenced by the polyp’s size and the presence of high-grade dysplasia, which indicates severe cellular abnormality. Sessile polyps larger than 10 millimeters are considered advanced lesions and have an increased risk of harboring or developing malignancy. Location is also relevant, as larger SSA/Ps in the upper colon are more concerning than small hyperplastic polyps in the lower colon.
Detection and Removal Methods
Colonoscopy remains the primary and most effective method for both detecting and removing sessile polyps. However, the flat nature of these lesions requires careful, high-quality examination. Advanced imaging techniques, such as chromoendoscopy or narrow-band imaging, are often utilized to better visualize the polyp’s margins and surface features.
Small sessile polyps, typically those under 10 millimeters, can be removed safely using a cold snare polypectomy, which uses a wire loop without electrical current. For larger or more complex sessile lesions, Endoscopic Mucosal Resection (EMR) is frequently employed. EMR involves injecting a solution beneath the polyp, lifting it away from the deeper muscle layer of the colon wall to create a protective cushion.
This submucosal injection allows the endoscopist to safely resect the broad-based polyp using an electrosurgical snare. EMR is often necessary because the direct attachment of sessile polyps makes standard snare removal less secure, increasing the risk of incomplete excision or injury to the colon wall. Very large sessile polyps may require removal in multiple pieces, a process called piecemeal resection, which ensures no residual tissue is left behind.
Post-Removal Surveillance and Follow-Up
Once a sessile polyp is removed, the tissue is sent for histopathology to determine its exact classification and potential for malignancy. The results of this analysis dictate the personalized schedule for future surveillance colonoscopies. This follow-up plan monitors the site for recurrence and detects any new polyps before they can progress to cancer.
Patients who had a sessile serrated polyp smaller than 10 millimeters without dysplasia are recommended to have their next colonoscopy in five years. If the pathology reveals a large sessile serrated polyp (10 millimeters or greater) or any sessile serrated polyp with high-grade dysplasia, the surveillance interval is shortened to three years. If a large sessile polyp was removed in fragments, a repeat colonoscopy to check the resection site is scheduled within six months to ensure complete removal. The surveillance interval is based on the most advanced polyp found, aligning the follow-up strategy with the highest level of risk.