Minimally invasive test provides best alternative to colonoscopy

14 February 2013

CT scanner

Image: CT scanner ©  Image courtesy of joncallas on Flickr

A new scan offering patients a less invasive diagnostic test for possible bowel cancer is more effective than the current radiological standard of barium enema, according to two studies led by University College London (UCL) and Imperial College London. The researchers say that the new scan should be considered alongside the 'gold standard' of colonoscopy. 

Computed tomographic colonography (CTC) is the name of the newer procedure. It is sometimes called 'virtual colonoscopy' because it uses a CT scanner and computer to generate 3D images of the colon. However unlike colonoscopy, where a flexible endoscope is passed along the large bowel, CTC is minimally invasive and does not require sedation. 

A barium enema is a different diagnostic test where x-ray pictures are taken while barium sulphate is put into the colon to improve the visibility. 

Despite the benefits of CTC the researchers urge caution. They state that guidelines are needed before CTC is used more widely because its ability to detect relatively unimportant findings can result in patients being referred for unnecessary follow-up tests. 

In the first trial, more than 3,800 patients were given either a CTC or a barium enema. The research showed that CTC was more effective than barium enema at finding bowel cancers and precancerous polyps. 

Professor Steve Halligan, Director of the UCL Centre for Medical Imaging, said: "Our trial shows that CTC is more accurate than barium enema. We hope that barium enema will now be phased out in favour of CTC and that the National Institute for Health and Clinical Excellence will update its guidelines.  

"Although CTC can be performed on standard CT scanners available in practically all NHS hospitals, many do not have radiologists with experience of looking at CTC scans. These radiologists will need training in order to deliver the results we observed in our trials." 

In the second trial, almost 1,600 patients were given either a CTC or a colonoscopy. Previous studies have shown that these two tests have similar sensitivity for detecting bowel cancer.  

Unlike colonoscopy, samples of tissue cannot be taken at CTC and it was previously not known how many patients needed a follow-up test to either confirm a suspected cancer or to rule out other findings from the scan. Similarly, it was not known how many patients needed a follow-up test after colonoscopy because the scope could not pass around the bowel. 

In patients who had CTC, 30 percent had a follow-up test compared with only eight per cent who had colonoscopy. Some of the follow-up tests after CTC were necessary because a possible cancer or large polyp had been seen. However, almost a third of follow-up tests were to investigate small polyps that could have been left alone as they were unlikely to develop into cancers.  

Professor Wendy Atkin of Imperial College London explained: "Understandably hospital doctors are cautious and request more tests after CTC. However, CTC detects unimportant findings, so guidelines are needed to help doctors decide who should have a further test. With these in place, we have shown that CTC offers a viable option for people who are not able to, or do not wish to, undergo a colonoscopy for whatever reason."  

Professor Jane Wardle of UCL led studies looking into patient experiences of the three tests. She added: "We have shown that people prefer CTC to both barium enema and colonoscopy. This research should mean that patients with bowel cancer symptoms can get the best test for them." 

The papers, Computed tomographic colonography versus barium enema for diagnosis of colorectal cancer or large polyps in symptomatic patients (SIGGAR): a multicentre randomised trial and Computed tomographic colonography versus colonoscopy for investigation of patients with symptoms suggestive of colorectal cancer (SIGGAR): a multicentre randomised trial, are published in The Lancet.

  • A new type of scan, called computed tomographic colonography, or CTC, is more effective than barium enema for diagnosing possible bower cancer, according to two studies led by researchers at University College London and Imperial College London. 
  • Currently, the standard options for diagnosis are barium enema and colonoscopy. The researchers say that, with proper guidelines in place, CTC - which is minimally invasive -should replace barium enema. 
  • However CTC was not the best approach for everyone. Patients with a history of inflammatory bowel disease, such as ulcerative colitis or Crohn's, were diagnosed significantly more frequently by colonoscopy than CTC.