High Definition Endoscopy With i-Scan for Small Colonic Polyp Evaluation: The HiScope Study

Traditionally all polyps detected at colonoscopy, except obvious cancers, have been removed. It is felt that small (<10mm diameter) hyperplastic polyps cannot be reliably distinguished from adenomatous polyps by endoscopists [1]. Therefore a large number of hyperplastic polyps are removed unnecessarily. This results in increased risk to patients through exposing them to unnecessary polypectomy, and increased cost to the health service through the cost of processing greater numbers of histopathology specimens. The cost per specimen is around £58.

This challenge of distinguishing small hyperplastic polyps from small adenomatous polyps has been met over the past decade through the use of novel chromoendoscopy and computed 'virtual chromoendoscopy' techniques.

Chromoendoscopy involves using staining or contrast dyes to highlight the minute surface patterns in the mucosa of the gastrointestinal tract. The dyes are applied to the colonic mucosa via the working channels of the endoscope. Vital stains such as cresyl violet and methylene blue, which are taken up into epithelial cells, have been used by Japanese endoscopists for many years. Work by Kudo et al showed that by using these stains in combination with magnification endoscopy the minute 'pit patterns' of colonic mucosal lesions could be precisely examined and classified. The pits described are the surface opening of the mucosal crypts. Kudo showed that the surface pit pattern could predict the histology of a lesion with high accuracy [2-4], enabling distinction between adenomatous and hyperplastic polyps. Concerns regarding potential harmful effects of vital stains increased the popularity of an alternative chromoendoscopy dye, indigocarmine [5]. Indigocarmine is not taken up by cells but lies on the colonic wall. Studies from East Asia, the USA and Europe published in the early part of the last decade showed that by combining indigocarmine and magnification endoscopy, neoplastic colonic polyps (adenomas) could be distinguished from non-neoplastic hyperplastic polyps with accuracy rates of 68-96% [6-10]. By the same method, surface patterns could also identify small early colorectal cancers[11] . Subsequent studies demonstrated that indigocarmine could adequately distinguish between adenomatous and hyperplastic polyps without the need for optical magnification [12-15].

During the past few years new methods of closely examining lesions within the colon have been developed. Digital imaging techniques or 'virtual chromoendoscopy' systems have been developed by endoscope manufacturers as a 'push-button' alternative to chromoendoscopy dyes, being potentially simpler and quicker to use. The first of these novel technologies available was the narrow band imaging (NBI) system produced by Olympus. A filter within the endoscope selects out narrow bandwidths of blue and green light, and thus reduces red light. These wavelengths penetrate only the superficial layers of the mucosa, highlighting surface patterns and microvasculature. Adenomatous polyps have more numerous and prominent microvessels in comparison to hyperplastic poylps. This system has been shown to be effective in differentiating small hyperplastic and adenomatous polyps with accuracies of 91 - 94% [16-23].

The Fujinon Intelligent Colour Enhancement (FICE) system developed by Fujinon uses post-processor electronic colour filter technology to allow a range of filter images with different wavelengths of light to be viewed. Similar results to NBI have been achieved in the characterisation of small polyps [13, 24, 25].

More recently a further virtual chromoendoscopy system, i-Scan has been developed by Pentax. i-Scan identifies areas of contrast between adjacent pixels (ie light bordering dark) and enhances this contrast. Additionally in a similar method to FICE, post-processor manipulation of the red, green and blue components of the spectrum is used to enhance vessels and surface structures.

A single study from Germany has suggested that i-Scan improves the detection of lesions during flexible sigmoidoscopy and can accurately predict histology. There is a need for further data on the clinical efficacy of i-Scan in the assessment of colonic polyps, particularly in a UK population and in a bowel cancer screening population, neither of which have been studied to date.

Through the use of these new technologies it may be possible to accurately predict the histology of small polyps in real time. Once an in-vivo diagnosis has been made with high confidence it may be possible for small hyperplastic polyps to be discarded, rather than sent for histological analysis, or to be left in situ [22]. This has potential benefits in reducing the frequency and consequent risk of polypectomy for patients and could also reduce pathology costs. UK and US guidelines for repeat surveillance colonoscopy after adenomas are detected at baseline examination are based on the number and size and histology of adenomas [26, 27]. At present these 'rescope intervals' are determined once the histology report of any resected polyps is received. With accurate in-vivo diagnosis these intervals may be set immediately after the baseline colonoscopy has been completed.

Whilst the development of these endoscopic advanced imaging technologies is to be welcomed, it is important for studies to determine what can be achieved through their use, over and above standard white-light colonoscopy. The American Society for Gastrointestinal Endoscopy has identified the utility of technologies used in the real-time assessment of diminutive (<5mm) colonic polyps as a key area for study, and has published guidelines on the minimum standards which new endoscopic technologies should meet before their use becomes widely adopted [28].

We aim to evaluate HDWL and HDWL + i-Scan for the real time assessment and prediction of histology of small colonic polyps in a BCSP population.