Sessile serrated lesions (SSLs) are a specific type of growth found within the colon that has gained increasing attention in gastrointestinal health. They differ from other, more commonly known colon polyps, necessitating a distinct approach to their identification and management.
Understanding Sessile Serrated Lesions
A sessile serrated lesion is a type of colonic growth characterized by its flat or subtly raised shape, which often makes it challenging to detect during routine examinations. The term “sessile” refers to this flat, broad-based attachment to the colon wall, unlike polyps that grow on a stalk. Under a microscope, these lesions exhibit a distinctive “serrated” or saw-tooth appearance of their cells, a key histological feature. SSLs are frequently found in the right side of the colon, particularly in the cecum and ascending colon.
Why These Lesions Matter
Sessile serrated lesions are significant because they can progress to colorectal cancer. They are considered precursor lesions in an alternative pathway of cancer development known as the “serrated pathway.” This pathway differs fundamentally from the more common adenoma-carcinoma sequence, which involves traditional adenomatous polyps. The serrated pathway is often associated with specific molecular changes, such as BRAF gene mutations and DNA hypermethylation, which can lead to microsatellite instability. While this progression may be slower than that seen in some conventional adenomas, the distinct molecular alterations make early and accurate identification of SSLs important for cancer prevention.
How They Are Detected
Colonoscopy remains the primary method for identifying sessile serrated lesions within the colon. Detecting SSLs presents unique challenges due to their characteristic flat or subtly elevated shape and their tendency to blend in with the surrounding colon lining, often having a similar color. To improve detection rates, endoscopists increasingly utilize advanced imaging techniques, such as high-definition endoscopes, chromoendoscopy, and narrow-band imaging. These specialized modalities enhance visualization by highlighting subtle mucosal changes or vascular patterns, making SSLs more discernible.
What Happens After Diagnosis
Once a sessile serrated lesion is diagnosed, the standard course of action involves its complete removal, typically through an endoscopic polypectomy performed during a colonoscopy. Due to their flat and often indistinct borders, achieving complete removal of SSLs can sometimes be technically challenging. Endoscopists must ensure that no residual tissue remains, as incomplete resection can lead to recurrence or continued progression. Following removal, surveillance intervals for subsequent colonoscopies are recommended, which may differ from those for conventional adenomas. These follow-up schedules are determined by factors such as the size of the removed lesion, the presence of dysplasia, and the total number of SSLs found, aiming to monitor for new or recurrent lesions.
Sessile Serrated Lesions vs. Other Polyps
Differentiating sessile serrated lesions from other common colorectal polyps is important for appropriate management and surveillance. Hyperplastic polyps, for instance, also exhibit a serrated microscopic appearance but are generally considered benign and typically do not carry a risk of malignant transformation. In contrast, conventional adenomas, such as tubular or villous adenomas, are characterized by cellular dysplasia and typically progress to cancer through a different molecular pathway than SSLs. Traditional serrated adenomas, while also serrated, are much rarer and often have a more polypoid or stalked morphology, resembling conventional adenomas, but with serrated features. The accurate classification of these polyps guides patient care, as each type carries a different level of cancer risk and requires specific follow-up recommendations.