What is a sessile serrated (precancerous) bowel lesion in an older adult over 50?

What is a Sessile Serrated Bowel Lesion?

A sessile serrated lesion (SSL), also called a sessile serrated polyp (SSP) or sessile serrated adenoma, is a precancerous colon polyp that accounts for up to 30% of colorectal cancers through a distinct molecular pathway separate from conventional adenomas. 1, 2

Key Defining Characteristics

Terminology and Classification:

• The terms sessile serrated polyp (SSP), sessile serrated adenoma, and sessile serrated lesion (SSL) are synonymous and refer to the same entity 1
• SSLs are a type of serrated polyp that are not dysplastic initially but can develop foci of dysplasia, at which point they are termed SSL with dysplasia (SSL-d) 1
• The WHO recently proposed using the term "sessile serrated lesion" as the preferred nomenclature 1

Histologic Features:

• SSLs show serrated architecture of the crypt lining epithelium with asymmetrical proliferation, irregular crypt shapes with branching, and crypt dilatations especially in the basal portions 3
• They differ from benign hyperplastic polyps by having abnormal proliferation patterns and architectural distortion 3
• SSLs typically lack the prominent surface blood vessel pattern seen in conventional adenomas 1

Clinical Significance and Cancer Risk

Malignant Potential:

• SSLs represent the major precancerous serrated lesion and are found in 8-9% of screening colonoscopies 1, 2, 4
• They account for 15-30% of all colorectal cancers through the serrated pathway, which involves the CpG island methylator phenotype (CIMP) with BRAF mutations 1, 2, 4
• Advanced SSLs (≥10 mm or with any dysplasia) are considered to have comparable cancer risk to advanced conventional adenomas 1

Distribution and Detection Challenges:

• SSLs are predominantly located in the proximal (right) colon, unlike conventional adenomas which are more evenly distributed 1, 2, 4
• They are typically flat or sessile in shape with few or no surface blood vessels, making them significantly more difficult to detect at colonoscopy than conventional adenomas 1, 2
• Up to 50% of large SSLs may be incompletely resected with standard techniques, contributing to interval cancer risk 2

Prevalence in Older Adults

Age-Related Findings:

• In adults aged 45-49 years, clinically significant serrated polyps (including SSLs) are found in 5.9% of screening colonoscopies, similar to the 6.1% rate in those aged 50-54 years 1
• The prevalence of SSLs remains relatively stable from age 40 onwards, unlike conventional adenomas which increase continuously with age 5

Management Implications

Risk Stratification:

• SSLs without dysplasia are generally managed like tubular adenomas 1
• SSL-d (with any grade dysplasia) are managed like high-risk adenomas and may require even more frequent surveillance 1
• Advanced SSLs are managed similarly to advanced adenomas given their comparable cancer risk 1

Common Pitfall:

• Pathologist variability exists in differentiating hyperplastic polyps from SSLs, leading to inconsistent reporting 2
• Endoscopically diagnosed hyperplastic polyps ≥10 mm are sometimes pathologically diagnosed as SSLs and should be considered for resection 6