Polyps are abnormal tissue growths found most commonly in the inner lining of the colon. These growths are common, especially as people age, and occur when cells divide abnormally. Because polyps can sometimes develop into cancer, precise classification is important for determining the right treatment and surveillance plan. The physical shape of the growth is a primary characteristic physicians identify. This article focuses on the sessile type, which carries unique health implications.
Understanding Polyp Shape: Sessile Versus Pedunculated
The term “sessile” describes a polyp that attaches directly to the colon lining with a broad, flat base. Visually, it appears as a raised bump or dome-shaped lesion flush against the organ wall, often compared to a small hill. This structure is distinct from pedunculated polyps, which are connected to the colon wall by a long, narrow stalk (pedicle), giving them a mushroom-like appearance.
The difference in attachment is significant for detection and removal. A pedunculated polyp stands out from the wall, making it easier to spot during a colonoscopy. Conversely, the flat nature of a sessile polyp causes it to blend in with the surrounding mucosal tissue, making it more challenging to find. The broad base means abnormal cells extend laterally into the tissue lining, rather than being confined to a narrow attachment point.
Medical Significance: Sessile Polyps and Cancer Risk
The sessile shape is medically significant because it is associated with a type of growth that follows an accelerated path to malignancy. A major concern is the Sessile Serrated Adenoma/Polyp (SSA/P), which is typically sessile and recognized as a precursor lesion for a substantial number of colorectal cancers. SSA/Ps progress through the “serrated neoplasia pathway,” a distinct process often involving the activation of the BRAF oncogene and subsequent instability in DNA repair.
SSA/Ps are estimated to originate 20 to 30% of sporadic colorectal cancers. These polyps are often found in the right side of the colon and are characterized by a microscopic, serrated appearance of the tissue glands. The transformation to cancer can occur more rapidly than the progression seen in traditional adenomas, making accurate identification and removal important. Furthermore, the flat profile of sessile polyps can complicate the removal process, potentially leading to incomplete resection and a higher risk of recurrence.
An SSA/P with signs of dysplasia (abnormal cell growth) carries a particularly high risk of developing into cancer. The subtle nature of these lesions means they may be missed during screening, contributing to “interval cancers” that appear between scheduled colonoscopies. The presence of an SSA/P indicates a patient is in a higher-risk category and requires a more rigorous surveillance schedule.
Clinical Approach: Detection and Removal
The detection of sessile polyps poses a challenge because their lack of a stalk allows them to lie flat against the colon wall, making them inconspicuous during a standard colonoscopy. Endoscopists must use careful technique and often specialized viewing modes, such as chromoendoscopy or narrow-band imaging, to highlight the subtle contours and surface patterns that distinguish these flat lesions from healthy tissue. Studies have shown a significant variability among physicians in the rate at which they detect sessile serrated polyps, underscoring the difficulty of this task.
Once a sessile polyp is identified, its broad attachment requires specialized removal techniques to ensure the entire lesion is excised. For larger sessile polyps, the standard procedure is often an Endoscopic Mucosal Resection (EMR). EMR involves injecting a lifting solution, such as saline, beneath the polyp into the submucosal layer. This creates a fluid cushion that elevates the sessile polyp away from the deeper muscle layer of the colon wall, allowing a snare to safely capture and remove the entire lesion.
This “lift and cut” method minimizes the risk of perforating the colon wall, a complication more likely when removing a sessile polyp compared to a pedunculated one. The goal is en bloc resection (removing the polyp in one piece), but larger lesions often require piecemeal removal. Patients undergoing piecemeal resection face a higher risk of recurrence, sometimes up to 18%. The completeness of the initial removal dictates the necessary follow-up, which often involves a repeat colonoscopy within six months to a year to ensure no tissue remains.