Endoscopy Suite

JUNE 13, 2023

Finding and Managing Sessile Serrated Polyps Can Be Challenging

Sessile serrated polyps pose a unique challenge to endoscopists. They are easy to miss, can be incompletely resected and are thought to become cancerous more quickly than conventional adenomas, according to experts.

“The sessile serrated polyps [ssPs] are kind of like the new polyps on the block,” said Robin B. Mendelsohn, MD, the clinical director of the Gastroenterology, Hepatology, and Nutrition Service and co-director of the Young Onset Colorectal and Gastrointestinal Cancer Center at Memorial Sloan Kettering Cancer Center, in New York City. “We’re pretty familiar with the routine colon polyps, which are tubular adenomas,” Dr. Mendelsohn noted. In contrast, “sessile serrated polyps are these flat polyps that can be found anywhere in the colon but are often found on the right side of the colon, and they’re difficult to see and spot.

“Even when you do see them, a lot of times they might be bigger than you initially think,” Dr. Mendelsohn said. “We do know that these … progress to colon cancer, just on a different pathway than the tubular adenomas.”

ssPs are now estimated to produce about 15% to 30% of sporadic colorectal cancers, but they were rarely detected before 2010, noted Seth Gross, MD, the clinical chief of gastroenterology and hepatology at NYU Langone Health in New York City, during a presentation at the 2022 New York Society of Gastrointestinal Endoscopy annual course. Instead, ssPs were lumped with other nonconventional adenomas and considered hyperplastic polyps, and existing guidelines typically suggested that the group as a whole was benign, Dr. Gross added.

Pathologic Continuum

Today, serrated polyps are classified as hyperplastic polyps (HP), ssPs, or traditional serrated adenomas (TSA) (Table). HPs, which make up 90% of serrated polyps, have no dysplastic potential (Figure 1). ssPs, which make up about 10% of serrated polyps are proximal, flat and pale, and have dysplastic potential (Figure 2). TSAs are very rare, pedunculated and distal, and are already dysplastic (Figure 3).

Features	Hyperplastic polyps	Sessile serrated lesions	Traditional serrated adenomas
Table. Classification of Serrated Polyps
Clinical characteristics
Prevalence	20%-30%	5%-15%	<1%
Size	Usually small or diminutive (= 5mm)	Usually larger than hyperplastic polyps (mean diameter, 5-7 mm)	Usually larger than ssLs
Morphology	Flat or sessile	Flat (45%) or sessile	Polypoid or pedunculated
Endoscopic appearance
White light	Pale or same color as surrounding mucosa Round or oval shape Flatten with insufflation Absent or fine, lacy vessels	Mucous cap Ring of debris Cloud-like surface Irregular shape	Erythematous Multilobulated “Pine cone” appearance Type IV-S pit pattern
Narrow band imaging	NICE type 1 Uniform or dark or white spots	NICE type 1 WASP criteria Dark spots in crypts	Characteristics not well defined
NICE, National Institute for Clinical Excellence; ssLs, sessile serrated lesions; WASP, Workgroup serrAted polypS and Polyposis. Based on Gastroenterology 2019;157:949-966.

HPs and TSAs probably exist along a continuum, and categorization is likely to vary between pathologists, according to Dr. Gross. In terms of clinical significance, HPs that are 1 cm or larger are equivalent to ssPs, and those 5 to 9 mm may be misdiagnosed ssPs. Small rectosigmoid HPs are not clinically significant, Dr. Gross said.

Figure 1. Hyperplastic polyp with serrations on histology (no dysplastic potential).

Courtesy of Joseph Anderson, MD.

Figure 2. Sessile serrated polyp with dysplastic potential. Histolology shows cystic change at the base and boot-shaped crypts.

Courtesy of Joseph Anderson, MD.

Figure 3. Traditional serrated adenoma. Histology shows dysplasia (nuclear enlargement and stratification).

Courtesy of Joseph Anderson, MD.

Dr. Gross also discussed long-term CRC risks, and noted that for polyps 1 cm or larger, serrated polyps carry risks for CRC that are similar to those associated with advanced adenomas (HR, 4.2; [95% CI, 1.3-12.3] vs 3.3; [95% CI, 2.1-5.2], respectively) (Gut 2015;64[6]:929-936).

Better Detection Needed

Those increased risks should encourage gastroenterologists to put emphasis on improving detection of ssPs, according to Dr. Gross. “We talk about the adenoma detection rate and seeing improvements among endoscopists, but we don’t hear physicians say what their ssA [sessile serrated adenoma] detection rate is. I think ssA detection is another measure physicians should track and aim to improve,” he said.

To improve ssP detection rates, he suggested various strategies, including an adequate withdrawal time, diligently washing debris on the colonic mucosa, and closely inspecting as much of the colon wall surface area as possible.

“Sessile serrated polyps are easily missed, due to subtle features seen on colonoscopy.” He said the features can include a mucous cap, a nodular surface, draping over colon folds and “a rim of debris.” In addition, they may “obscure the blood vessel seen on the colon wall, [be] dome shaped, and [have a] red or pink color very close to normal colon wall color,” Dr. Gross told Gastroenterology & Endoscopy News. When uncertain, he said he injects dye to improve visualization.

The consequences of missed ssPs could be significant. Each 1% increase in proximal ssP detection is associated with a 7% decreased risk for interval cancer, whereas a 1% increase in adenoma detection is associated with a 3% decreased risk for interval cancer, Dr. Gross said.

“So clearly there is a difference between adenoma and serrated polyp pathways to colon cancer,” Dr. Gross said. “Clinically it is believed the sessile serrated polyp has a shorter timeline to developing colon cancer compared to traditional adenoma,” he said.

Detection Assisted by AI

Dr. Mendelsohn suggested that artificial intelligence can be a useful supplement during colonoscopy to help find subtle lesions. “Even before we had AI, I always told everyone in the room, keep your eyes out, because the more eyes, the more helpful. There’s a known miss rate, even in the best of hands. We don’t usually miss big things, but the more eyes on it the better, and I think that AI just acts as another help,” she said. Sometimes AI can help identify a lesion, she said, and sometimes “if you see something and then the patient moves or something happens and you lose it, [AI] can help you find it again.”

Dr. Mendelsohn said that gastroenterologists “need to be open to new techniques” to help increase their adenoma detection rates as well as their ssP detection rates, which, she added, “should emerge as part of our quality indicators.”

Margin Ablation Can Improve Resection of Large Serrated Polyps

The local recurrence rate for serrated lesions larger than 15 mm is high, and thermal ablation of margins during resection is superior to no ablation in reducing recurrence of sessile serrated lesions larger than 20 mm, according to a recent study.

Incomplete resection has been linked to both polyp size and histology, according to Laetitia Amar, MD, who presented the study’s findings at the 2023 Canadian Digestive Diseases Week.

“The current paradigm for the resection of large serrated lesions is that recurrence is low, with an increased interest in using cold methods of resection for these lesions,” said Dr. Amar, an internal medicine resident at Montreal University Hospital Research Center. However, she said, “These studies included mostly polyps of 10 to 14 mm, and very few were above 20 mm, which potentially biased results toward (lower) local recurrence rates.”

Dr. Amar said that in their recent study “the local recurrence rate after cold snare was actually pretty high, at 24%, and it was even higher when we restricted the analysis to above 20-mm lesions.” Local recurrence rates were much lower when endoscopic mucosal resection (EMR) was combined with thermal margin ablation. She acknowledged that the study included some challenging lesions, such as peri-appendiceal lesions that other studies likely excluded.

For the study, she and her co-investigators examined local recurrence rates after EMR, EMR with thermal ablation (EMR-T), or cold snare polypectomy (CSP) of large colorectal serrated lesions.

They included 170 adults who underwent resection of sessile serrated lesions, traditional serrated adenomas and hyperplastic polyps and had colonosocpy follow-up within 18 months at Montreal University Hospital Center between 2010 and 2022. Resections included a total of 191 polyps at least 15 mm in size. The population was mostly female (59.8%), with a mean age of 65 years. The median polyp size was 22.4 mm, and 56.0% were 20 mm or larger.

The overall local recurrence rate was 18.8%, including 16.8% for polyps 20 mm or larger and 17.9% for polyps 30 mm or larger. The local recurrence rate was 5.1% with EMR-T, versus 23.2% with EMR (P=0.013) and 23.1% with CSP (P=0.031).

—J.K.

Beyond deteection, it’s also important to achieve a complete resection, but that can be difficult, and recurrences do occur. The CARE (Complete Adenoma Resection) study found an incomplete resection rate of 10.1% for adenomas and 31.0% for ssPs (P=0.043) (Gastroenterology 2013;144:74-80). Options to reduce incomplete resection include use of endoscopic mucosal resection (EMR) (see box).

“The problem with these lesions versus a traditional adenoma is that you can’t always appreciate the borders,” said Dr. Gross. “You think you got it, but you don’t know for sure. So I encourage you, before you do any resection, to really make sure that you know where these edges are. The larger the lesion, the more likely we risk an incomplete resection of sessile serrated lesions.”

—Jim Kling

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