'Underwater' Colonoscopy Amplifies Polyp Detection

Damian McNamara

May 11, 2017

CHICAGO — An "underwater" technique allows physicians to detect significantly more polyps during colonoscopy than traditional air insufflation, according to researchers, but not everyone agrees that the new approach is warranted.

"Gastroenterologists who are doing a high number of screening colonoscopies, in particular, should consider using underwater techniques to improve detection of polyps," said study investigator Anish Patel, MD, from the UC Irvine Medical Center in California.

The technique can be used routinely, but it is indicated for patients at higher risk because of a family history of colon cancer or a history of diseases that can predispose a person to cancer, such as inflammatory bowel disease, he said here at Digestive Disease Week 2017.

The use of water to "float" the mucosa magnifies lesions, making detection easier, he told Medscape Medical News.

Studies have shown that underwater colonoscopy improves patient comfort because the water distends and straightens the sigmoid colon, he explained. It has been reported that removing a colonoscope from that first part of the colon can "cause a lot of pain," he added.

"Even in patients not at higher risk, this technique, if nothing else, can leave them more comfortable and encourage them to continue to get appropriate screening," he pointed out.

However, "there is some debate about the value of water and water emulsion," said Subhas Banerjee, MD, from the Stanford University Medical Center in California.

Some physicians report that it takes more time, and others question the value of making patients more comfortable if you have them under sedation anyway, he explained.

"Because of this controversy, it has not yet been widely adopted," Dr Banerjee reported.

They started to see polyps they might not otherwise have noticed.

"It does remain controversial, and you can find papers on both sides of the issue," Grace Elta, MD, from the University of Michigan at Ann Arbor, said during a news conference at the meeting. "A lot of endoscopists have gone toward CO₂ insufflation," which is less uncomfortable than air.

"One of the reasons we were inspired to look at this particular technique — we didn't invent it, it already existed — is because two of our most prominent endoscopists are fans of it," said study investigator Jasleen Grewal, MD, who is also from UC Irvine.

"They started to see polyps they might not otherwise have noticed," she told Medscape Medical News. "They felt their detection rates were increasing, and that is what inspired us to see if there really is a difference."

For their study, Drs Patel, Grewal, and their colleagues examined colonoscopies performed at UC Irvine for any reason from September 2014 and November 2016. They identified 1987 underwater colonoscopies and 1959 air insufflation colonoscopies. No new equipment was required for the water technique, and the same rooms were used for both types of procedure.

The rate of detection for right-side colon polyps was significantly better with underwater colonoscopy than with air insufflation (53.1% vs 47.3%; P < .0005), as was the rate of sessile serrated adenomas in the right colon (9.6% vs 6.6%; P < .0005).

Table. Detection Rates With the Two Techniques

Type of Lesion Underwater Colonoscopy, % Air Insufflation, % P Value
Polyp 69.6 64.3 <.0005
Adenoma 44.4 41.4 .05
Sessile serrated adenoma 11.1 7.9 .0005


Sometimes water can buoy lesions that are very flat and make them easier to see and remove, Dr Patel explained.

"A large part of the time, those lesions lead to colon cancer, even in patients who are being appropriately screened, just because they are missed and not removed," he said.

"Identifying those lesions could reduce rates of what we call interval cancers, which happen in between screening with colonoscopy," he added.

"The popularity of water-based colonoscopy has increased in the past few years. I've used it myself for many, many years," said Dr Banerjee. "It comes with some advantages. As you inject the water, it helps to wash off any residual stool in the colon, so you get a better, cleaner look later. The water also acts as a magnifier; some polyps you might have missed using air get magnified under water."

"It does take longer in some hands, but patients tend to like it better," he added. Although previous studies have reported longer procedure times, the difference between the underwater and air procedures in this study was not significant (30.3 vs 31.7 minutes; P = .18).

Dr Patel, Dr Banerjee, and Dr Elta have disclosed no relevant financial relationships.

Digestive Disease Week (DDW) 2017: Abstract 953. Presented May 9, 2017.

Follow Medscape Gastroenterology on Twitter @MedscapeGastro and Damian McNamara @MedReporter


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