What is the appropriate management and surveillance interval for a lower rectal traditional serrated adenoma (TSA) with high‑grade dysplasia and no invasive carcinoma?

Management of Traditional Serrated Adenoma with High-Grade Dysplasia in the Lower Rectum

A traditional serrated adenoma (TSA) with high-grade dysplasia in the rectum requires surveillance colonoscopy at 3 years, following the same high-risk surveillance protocol as conventional adenomas with high-grade dysplasia. 1

Immediate Management Considerations

• Confirm complete excision of the TSA before establishing any surveillance schedule, as incomplete resection significantly increases recurrence risk and future colorectal cancer (CRC) risk 1
• If the lesion was removed piecemeal and measured ≥20 mm, perform a site check colonoscopy at 2-6 months to verify complete removal 1
• For TSAs between 10-20 mm removed piecemeal, endoscopist discretion determines whether a 2-6 month site check is needed based on confidence in complete excision 1

Risk Stratification and Rationale

TSAs with dysplasia carry substantially elevated CRC risk comparable to advanced conventional adenomas:

• TSAs with dysplasia have a 4.8-fold increased risk of future CRC compared to patients without polyps, placing them in the highest risk category 1
• Traditional serrated adenomas are specifically classified as "advanced serrated polyps" requiring intensive surveillance 1
• The presence of high-grade dysplasia in any serrated lesion elevates risk to the same level as conventional adenomas with high-grade dysplasia 1

Surveillance Protocol

First surveillance colonoscopy at 3 years after confirmed complete resection 1

This recommendation is based on:

• US Multi-Society Task Force 2020 guidelines explicitly include TSAs in the 3-year surveillance category 1
• British Society of Gastroenterology 2017 position statement recommends 3-year surveillance for serrated lesions with dysplasia, including TSAs 1
• The 2020 BSG/ACPGBI guidelines confirm that TSAs with dysplasia have CRC risk equivalent to advanced adenomas 1

Subsequent Surveillance Strategy

After the first 3-year surveillance colonoscopy:

• If normal or only 1-2 small tubular adenomas <10 mm are found: extend interval to 5-10 years 1
• If any high-risk features recur (≥3 adenomas, any adenoma ≥10 mm, villous features, high-grade dysplasia, or any serrated polyp ≥10 mm): continue 3-year intervals 1
• If new advanced serrated polyps are detected: maintain 3-year surveillance 1

Special Considerations for Rectal Location

Rectal TSAs warrant particular attention:

• TSAs are more commonly found in the rectum compared to sessile serrated lesions 1
• Rectal cancers have higher local recurrence rates (1.1%-6.3%) compared to colonic cancers (0%-1.9%) due to anatomic constraints 1
• After curative endoscopic resection of rectal neoplasia with high-grade dysplasia, some experts recommend more intensive early surveillance with flexible sigmoidoscopy every 3-6 months for the first 2 years, though this is primarily based on rectal cancer data rather than TSA-specific evidence 1

Critical Prerequisites for This Surveillance Plan

The 3-year surveillance interval assumes high-quality baseline colonoscopy:

• Complete examination to cecum with photodocumentation of cecal landmarks 1
• Adequate bowel preparation sufficient to detect polyps >5 mm 1
• Complete polyp resection with both endoscopic and pathologic confirmation 1
• Performed by colonoscopist with adequate adenoma detection rate 1

If any of these quality metrics were not met, repeat colonoscopy sooner to establish proper baseline 1

Additive Risk with Synchronous Adenomas

If conventional adenomas were also present at baseline:

• Calculate surveillance intervals separately for the adenoma findings and the TSA findings 1
• Use the shortest recommended interval between the two calculations 1
• Evidence suggests risk may be more than additive when serrated lesions and adenomas coexist, with odds ratios reaching 16.04 for synchronous advanced adenomas and serrated lesions versus 3.86 for advanced adenomas alone 1

Evaluation for Serrated Polyposis Syndrome

Assess whether this patient meets WHO criteria for serrated polyposis syndrome (SPS):

• ≥5 serrated polyps proximal to sigmoid with ≥2 being >10 mm, OR
• Any number of serrated polyps proximal to sigmoid in patient with first-degree relative with SPS, OR

• 20 serrated polyps of any size throughout colon 1

If SPS criteria are met: surveillance intensifies to every 1-2 years after clearing all polyps >5 mm 1

Common Pitfalls to Avoid

• Do not treat this as a simple hyperplastic polyp requiring no surveillance—TSAs with dysplasia are high-risk lesions 1
• Do not extend surveillance beyond 3 years for the first follow-up, even though the lesion is in the rectum—location does not reduce risk 1
• Do not perform fecal occult blood testing during the surveillance period, as colonoscopy is the appropriate modality 1
• Do not assume complete resection without endoscopic and pathologic confirmation—recurrence rates for serrated lesions can reach 7% at 12 months even after apparently complete resection 1