What Are Sessile Serrated Lesions

These are small growths occurring in the large intestines, also known as polyps, with  a characteristic ‘saw tooth like’ appearance under the microscope, and a tendency to become cancerous.¹ They need to be differentiated from other similar polyps which are not precancerous. These polyps rarely cause symptoms and are often detected at cancer screening tests.

Overview

The word polyps means a small, ‘mushroom-like’ growth with a stalk, that can occur in many passages of the body like intestines or even stomach. The ones in the large intestines are called ‘ colonic polyps’. There are different types of colonic polyps and one of them is sessile serrated lesions.  Sessile means the stalk is broad and flat rather than thin. Sessile serrated lesions are special for their microscopic ‘saw tooth / serrated’ appearance and also for their tendency to become cancerous. Once detected, they need to be removed completely by surgery and may need follow up.

Are sessile serrated lesions the only polyps in the intestines?

No, they are not the only polyps in the large intestines. 

Polyps in the large intestines(colon)  can be broadly categorized into two.

1. Polyps with serrations (serrated polyps): These include the following;

• Hyperplastic polyp - with just superficial serrations and no definite tendency to become cancer*
• Sessile serrated lesions(SSLs) (discussed here)
• Traditional serrated adenomas(TSAs) -show serrations and other features
• Mixed polyps

*There is some debate currently that a certain subtype of hyperplastic polyps can grow into SSLs and that they are both in the same spectrum. This has not been clearly established yet.¹²

2. Polyps without serrations (adenomatous polyps)

• Tubular adenoma 
• Tubulo villous adenoma
• Villous adenoma

3 Other polyps

There are also several other non cancerous polyps like inflammatory polyps in this category

What polyps are neoplastic polyps or in other words, can become  cancerous?

• All adenomatous polyps
• Sessile serrated lesions
• Traditional serrated adenomas 

What are the symptoms of sessile serrated lesions?

These lesions hardly cause symptoms like blood in stools because bleeding from them is rare, unlike outright cancerous lesions. Sessile serrated lesions are often detected on bowel cancer screening tests.

What are the available colonic cancer screening and detection tests?⁴

• FIT -This is called Fecal immunohistochemical test.⁸ This is a test that is usually used in the UK as the screening test. You will be given a tube/container to collect a sample of stools and the tube has a stick in the lid. You will be given instructions on how to close it and send it back safely. This test can detect blood in the stools that is present in such small amounts that it is not usually visible in the stools. The screening program in the UK will send this to eligible candidates as part of bowel cancer screening programme.⁸ If the test becomes positive you will be offered a sigmoidoscopy or colonoscopy. 

• Fecal occult blood testing - (FOBT)-This test also detects blood in your stools if they are at a minute level and not visible.(occult blood). This test can be positive in some polyps or cancers that bleed. If the test becomes positive, you will be offered a sigmoidoscopy or colonoscopy. This test is used in some countries for screening.

• Sigmoidoscopy or colonoscopy : Both these are tests where large intestines are viewed through a camera in a tube that will be introduced to your large intestines from your anus. (while you are sedated). Sigmoidoscopy is done for a limited and nearest part of your large intestines while colonoscopy means examining the entire length of large intestines. This used to be a part of the screening program but it is no longer used in that capacity and is only offered after a positive FIT test.⁸

• Virtual Colonoscopy (CT colonography) - In this test, instead of inserting a tube into your intestines from the anus, the colon is viewed through a series of CT scans to visualize the lesions in the intestines. This is done on people who are unfit for colonoscopy. The imaging may not be as clear as direct camera vision, for some lesions.
• Colonic capsular endoscopy- This test is done when you are given a small camera, which is the size of a large pill, to swallow. When it passes through your intestines it takes photographs that are transmitted to a screen and then the camera will pass through with your stools in a day or two.

If sessile serrated lesions are not usually symptomatic, how are they discovered?

The UK has a bowel cancer screening program which offers a bowel cancer screening test to selected, older individuals. This is the  fecal immunochemical testing(FIT).⁸ If this test becomes positive, which it can be, if there is a growth in the intestines, you will be offered a colonoscopy which can then detect this type of polyp. 

Which part of the colon are sessile serrated lesions usually located at?

Sessile serrated lesions are reported to be more common on the right side of the bowel meaning, caecum and ascending colon rather than the left and distal part of bowel like rectum or descending colon where hyperplastic polyps tend to occur.¹³

How are sessile serrated lesions diagnosed?

• Colonoscopy - Mentioned above
• Biopsy/sampling - During colonoscopy, a small sample from the polyp can be taken to send to the pathology laboratory where it will be processed and viewed under the microscope to confirm a sessile serrated lesion. In some cases the entire polyp will be removed via polypectomy or a method called endomucosal resection¹ and again sent to the pathology lab for confirmation.

What should I look for in my pathology report that says ‘ sessile serrated lesion?

• Whether the sample was a biopsy meaning only a part of the lesion was taken, in which case the lesion needs to be removed by another procedure.
• Whether it was a polypectomy or endomucosal resection in which case the lesion was attempted for complete removal.
• Whether the polypectomy/endomucosal resection margins were clear or in other words, was the removal complete.
• Whether there was dysplasia or not; dysplasia meaning early changes of cancer are present or not.

Are there different types of sessile serrated lesions?

There are mainly two types.

• Sessile serrated lesions with dysplasia
• Sessile serrated lesions without dysplasia

Dysplasia means an early cancerous change in the lesion. 

How do you treat sessile serrated lesions? (SSLs)

These need to be removed surgically with clear margins. The polyps are usually removed by a procedure called polypectomy or endomucosal resection.¹

In either case, the specimen will be sent to the pathology lab and processed and examined under the microscope to confirm the diagnosis and also to ensure the surgical margins are clear of the lesion.

What is the follow up protocol for SSLs?

If you have had a sessile serrated lesion, your follow up depends on whether you had multiple polyps, the size/s, the appearance under the microscope and whether there was dysplasia.⁶

Your doctor will assess all this and arrange a follow up plan for you either with another colonoscopy or a less invasive test like fecal occult blood testing.

What is serrated polyposis syndrome?⁶

This is a combination of serrated polyps of different sizes and numbers that is identified as a syndrome.⁶ The presence of this syndrome increases the risk of having a future colon cancer substantially. Therefore if your doctor finds this, you may have to undergo more frequent screening colonoscopy tests.

Do  SSLs become colon cancer?

They are called pre malignant polyps, meaning they can become cancer later. This is through a genetic defect, which is one of the pathways from which colon cancer develops. There are also other pathways for cancer to develop in the colon.

Is there a genetic reason behind SSLs?

SSLs often have a genetic defect in them called the BRAF mutation. This mutation is also seen in some non colonic cancers. 

Is there a way to prevent SSLs?

There are some reports that claim that a high-fat diet, high consumption of meat, alcohol, smoking and a high body mass index increases the risk of colonic polyps in general and even increases risk of cancer.²

Therefore limitation of these factors may help in prevention.

FAQ's

Are sessile serrated lesions the same as hyperplastic polyps?

No they are not. Hyperplastic polyps have some mild serrations but do not have some other features of SSLs. Also they are not considered pre malignant generally.

Are sessile serrated lesions the same as tubular adenomas?

No, they are not. The tubular adenomas show a different appearance under the microscope.

Summary

Sessile serrated lesions are a type of polyps in the intestines that can become cancerous. They have a special appearance, with a broad base and a saw tooth-like appearance under the microscope. They may or may not have dysplasia meaning early cancerous change. They need to be differentiated from other polyps and need removal completely. Regular follow up is essential.