Colonic Polyps

What are polyps?

Polyps are growths on the bowel wall, and some can develop into cancer over time. The risk of cancer is the reason that polyps are removed during colonoscopies. They are the most common finding during a colonoscopy, present in about 60% of people.

How are polyps removed?

Polyps are removed during a colonoscopy through a process called polypectomy. Small metal loops, either using a slicing technique or electricity, are passed through the colonoscope to remove the polyps. Larger polyps may require more advanced procedures, such as Endoscopic Mucosal Resection (EMR) or Endoscopic Submucosal Dissection (ESD), which need specialized expertise.

Polyps develop on the innermost layer of the bowel wall, called the mucosa, and beneath it is a thicker layer, the submucosa, followed by the outer muscle layer, the muscularis propria. The goal of polypectomy is to remove the polyp from the mucosa without damaging the deeper muscularis propria, as this can cause a perforation (hole) in the bowel.

Most polyps can be safely removed using a cold snare, which slices through the polyp without the risk of perforation or delayed bleeding. Thicker polyps require an electric knife (hot snare), which uses heat to cut, but carries a higher risk of damaging the muscularis propria. To reduce this risk, a fluid cushion may be injected into the submucosa to protect the muscle layer.

When a large polyp needs to be removed in several pieces, the procedure is called Endoscopic Mucosal Resection (EMR). This technique often requires significant submucosal injection and skill, with some risk of perforation, especially in areas where the bowel wall is thinner.

What is Underwater EMR?

Underwater Endoscopic Mucosal Resection (EMR) is a newer technique to remove large polyps from the bowel wall that appears to be easier, safer and more effective than the traditional method.

In 2010/2011, Dr Binmoeller at Interventional Endoscopy Services in San Francisco noted that when the colon is in a relaxed state filled only with water, ultrasound examination of the wall layers showed that the submucosa layer remained very thick, and would not require submucosal ‘cushion’ injection to protect the muscularis propria. This led to the technique of ‘underwater EMR’ (UEMR), which allows seamless removal of large polyps quickly and simply while doing a water-assisted colonoscopy.

Data from Dr Binmoeller’s group and Dr Rees Cameron’s own experience also suggests that UEMR reduces the risk of incomplete excision of large polyps, which can occur in up to 25% of cases performed by traditional EMR. An incompletely removed polyp is a risk for cancer, and means repeat colonoscopies until it is removed completely.

Watch a video on the underwater EMR technique.

What is Endoscopic Submucosal Dissection?

More than 20 years ago, Japanese endoscopists developed a new technique for removing early cancers of the stomach called endoscopic submucosal dissection (ESD). This technique uses an electric knife, rather than a snare, to cut around and under the lesion, allowing even large lesions to be completely removed in one piece. Gradually the use of this technique was broadened for early cancers throughout the gut and become widespread in east Asia, though not elsewhere in the world due to the high skill level required to perform it.

It was only in the 2010’s that ESD began to be widely performed outside of Asia, and Dr Cameron performed the first treatment of early oesophageal cancer with ESD in New Zealand in 2015. At present there are still only around 10 endoscopists performing ESD in NZ.

With increasing numbers of colonoscopies being performed in NZ, and more large polyps and early cancers being found, ESD is a valuable tool to allow the best opportunity to be cured by colonoscopy alone.