Both "stand-up" and flat polyps can be removed during colonoscopies in the vast majority of cases, said Dr Vikneswaran Namasivayam, consultant in the department of gastroenterology and hepatology at the Singapore General Hospital.

The techniques are similar although not identical.

Stand-up polyps protrude into the large intestine and, hence, can be identified easily.

They are removed using a technique called polypectomy.

A lasso-like snare is inserted through the scope and used to grip the polyp.

The polyp is then cut with the application of electrical energy and then removed.

Flat polyps are harder to grip this way as they do not protrude into the intestine but grow along the wall. If it is a small flat polyp, doctors can use forceps to grab it and then apply a current to burn it.

However, if it is large, the electric current needed could damage the colon wall or burn a hole in it, said Dr Ho Kok Sun, a general surgeon at Mount Elizabeth Hospital.

Usually, a solution will be injected below the polyp to lift it off the wall of the colon.

Numerous different techniques and instruments can then be used to remove the entire polyp.

This includes using a lasso-like snare and a cutting device.

If the gap is large after the polyp is removed, there are endoscopic clips that allow the defect to be closed.

These clips will drop out once the lining has healed, said Dr Ho.

Technology and techniques have improved over the years.

Techniques such as dye spraying and narrow band imaging (NBI) help detect flat polyps by enhancing the contrast between the normal colon lining and a flat polyp, said Dr Ho.

Dye spraying has been available in Singapore since the 1990s, while NBI technology has been available since 2004.

The detection of both conventional and flat polyps requires a careful assessment during a colonoscopy, added Dr Vikneswaran.

Preparation is also vital. Patients are instructed to take laxatives prior to a colonoscopy.

This typically entails consuming several litres of liquid laxative the evening before and on the morning of the colonoscopy.

If the colon is not clean enough, the procedure may have to be abandoned and rescheduled, which wastes time and money, said Dr Vikneswaran.

Ng Wan Ching