Colonoscopy is a diagnostic fibreoptic investigation that enables growths in the bowel (polyps) to be detected. Some of these polyps can develop into cancer. Although colonoscopy is the most accurate available test for the detection of these growths, some polyps, especially smaller ones, can be missed for a variety of reasons, including how well the polyp can be seen against the background of the normal lining of the large intestine (mucosa). It is important to identify even small polyps, which are often the precursors to cancer. Dye spraying (chromoscopy) is one of the simpler ways to make polyps stand out against the normal bowel mucosa, and hence be more easily seen.
We aimed to evaluate whether or not chromoscopy improves polyp detection in people undergoing screening for colorectal cancer.
Following a rigorous review of the literature, we included seven studies in our analysis with a total of 2727 participants. We included all studies that compared chromoscopy and conventional colonoscopy of the entire colon in people at risk of having polyps. The participants in the studies varied, however all were considered to be at low or average risk of developing polyps.
All the included studies randomised people to either conventional colonoscopy or chromoscopy. Two trials used a study design that differed from the others, by performing a conventional colonoscopy in all people first and removing any polyps observed, then randomising people to either conventional colonoscopy or chromoscopy. The goal of these studies was to determine the number of extra polyps identified with the two techniques, rather than the total number of polyps.
The analysis showed that the rate of detection of small polyps was improved by chromoscopy by about 90%. Of even greater clinical importance, the analysis showed that the detection of small polyps that could potentially develop into cancer was increased by about 30% when chromoscopy was used. The detection rate was not different in people with large polyps or cancer, as these are easily enough seen at conventional colonoscopy. No adverse events were reported related to the use of the contrast dye.
Quality of the evidence
There were drawbacks to the quality of the evidence based on methodology. On a basic level, study designs of this type do not allow blinding of the examiner. More subtle variations in study design also introduced variation in the data that could impact the reliability of the results. For example, in some studies the time spent examining the colon was standardised in both people undergoing chromoscopy and those undergoing conventional colonoscopy, whereas in other studies it was not; as the time spent examining the bowel will influence the number of polyps detected, and this standardisation does not reflect clinical practice, this makes generalising results from these studies to clinical practice more difficult. Other potential causes of variation included the different points of randomisation of participants (that is before the single colonoscopy or before a second procedure, that latter which as highlighted earlier looks only at additional polyps identified) and the reasons for the people undergoing colonoscopy (for example people taking part in a general screening programme may have smaller and less easily detected polyps than those presenting with symptoms).
There is strong evidence that chromoscopy enhances the detection of neoplasia in the colon and rectum. People with neoplastic polyps, particularly those with multiple polyps, are at increased risk of developing colorectal cancer. Such lesions, which presumably would be missed with conventional colonoscopy, could contribute to the interval cancer numbers on any surveillance programme.
Although conventional colonoscopy is the most accurate test available for the investigation of the colorectum for polyps, data exist that raise concerns about its sensitivity. Chromoscopy (spraying dye onto the surface of the colon to make polyps more visible) may be one way of enhancing the ability of colonoscopy to detect polyps, particularly diminutive flat lesions, which otherwise may be difficult to detect.
To determine whether the use of chromoscopy enhances the detection of polyps and neoplasia during endoscopic examination of the colon and rectum.
We searched the following databases: Cochrane Colorectal Cancer Group Specialised Register (October 2015), Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Library; Issue 10, 2015), MEDLINE (January 1950 to October 2015), EMBASE (January 1974 to October 2015), and ClinicalTrials.gov and World Health Organization International Clinical Trials Registry Platform (both November 2015). We also handsearched abstracts from relevant meetings from 1980 to 2015. Search terms included 'randomised trials' containing combinations of the following: 'chromoscopy' 'colonoscopy' 'dye-spray' 'chromo-endoscopy' 'indigo-carmine' 'magnifying endoscopy'.
We included all prospective randomised trials comparing chromoscopic with conventional endoscopic examination of the whole of the colon and rectum. We excluded studies of people with inflammatory bowel disease or polyposis syndromes and any studies that combined chromoscopy with additional interventions (cap assistance, water-perfused, etc.).
Two review authors independently assessed the methodological quality of potentially eligible trials, and two review authors independently extracted data from the included trials. Outcome measures included the detection of polyps (neoplastic and non-neoplastic), the detection of diminutive lesions, the number of participants with multiple neoplastic lesions, and the extubation time.
We included seven trials (2727 participants) in this update. Five trials were of sufficiently similar design to allow for pooled results. Two trials differed substantially in design and were included in a subgroup analysis. All the trials had some methodological drawbacks. However, combining the results showed a significant difference in favour of chromoscopy for all detection outcomes. In particular, chromoscopy was likely to yield significantly more people with at least one neoplastic lesion (odds ratio (OR) 1.53, 95% confidence interval (CI) 1.31 to 1.79; 7 trials; 2727 participants), and at least one diminutive neoplastic lesion (OR 1.51, 95% CI 1.19 to 1.92; 4 trials; 1757 participants). Significantly more people with three or more neoplastic lesions were also detected, but only when studies that used high-definition colonoscopy in the control group were excluded (OR 4.63, 95% CI 1.99 to 10.80; 2 trials; 519 participants). None of the included studies reported any adverse events related to the use of the contrast dye.