New Endoscopic Techniques

New endoscopic techniques are being introduced to improve early identification of even minimal lesions and to take targeted biopsies in suspicious areas. These techniques do not replace colonoscopy but are second-level examinations [21].

Chromoendoscopy

Endoscopic dye-spraying can improve dysplasia detection [7, 19]. This procedure involves the application of a mucosal stain or pigment, usually by injection through an endoscopic spray catheter. Chromoendoscopy improves the detection of minimal colonic lesions, raising the sensitivity of the endoscopic examination and, once a lesion is detected, can allow lesion characterisation, increasing the specificity of the examination [21-24]. There are 3 general classes of stain:

- Contrast dyes (for example, indigo carmine 0.1%): These coat the colonic mucosal surface and neither react with nor are absorbed by it. When dye is sprayed on the surface, groove patterns becomes evident and so mucosal lesions are highlighted.

- Absorptive dyes: These are absorbed by different cells to different degrees. Methylene blue 0.1% after few minutes avidly stains noninflamed mucosae but is poorly taken up by areas of active inflammation and dysplasia.

- Reactive dyes: These react with epithelium or mucos-al secretion, producing detectable colour change. Colour use seems to be safe. The indigo carmine is poorly absorbed from the gastrointestinal tract. There is a theoretical risk of allergic reaction, but this has not been reported with intraluminal use. A recent study suggests that methylene blue can cause DNA damage after chromoendoscopy in patients with Barrett's oesophagus.

Description of Procedure

On insertion, all faecal fluid should be aspirated and adherent stool washed off to ensure optimal mucosal views. Any abnormalities seen on insertion should be biopsied or removed, as they may not be easily identified on extubation. When the cecal pole has been reached, intravenous drugs (scopolamine 20 mg or glucagon 1 mg) should be given to reduce spasm and haustral-fold prominence. Adequate air insufflation is necessary. A dye-spray catheter is inserted down the instrumentation channel and the tip protruded 2-3 cm, and an assistant can spray the stain with a syringe. Spraying should be done in segments of 5-15 cm. Once a segment has been sprayed, excess dye must be suctioned and mucosal examination begins; it is necessary to wait few seconds for indigo carmine to settle into the mucosal contours; methylene blue takes about 60 s to be absorbed. Once this segment has been examined, the next segment is sprayed and so on until the anal margin. On average, 60-100 ml of solution is required to spray the entire colorectal mucosa. Suspicious areas should be photographed, biopsied and the site endo-scopically resected or tattooed if necessary. Patients with multiple postinflammatory polyps present a dilemma because the mucosa is not smooth, making dysplasia detection difficult. The colonoscopist must remain alert for any polypoid lesion that does not have a smooth surface and should take biopsies.

Magnifying Colonoscopy

New-generation colonoscopes with lens system on the tip enlarge the imagine up to 140 times [25-27]. Magnifying colonoscopes can show anatomic details to discriminate inflammatory from neoplastic lesions and to establish inflammation extension [27, 28], which previously was detectable only by histopatho-logical examination. It has been reported that microscopic disease activity can predict relapse in patients with UC and so influence the treatment plan.

By matching chromoendoscopy and magnifying colonoscopy, it is possible to obtain a very detailed mucosal examination, and even to distinguish polyp types (pseudopolyp, hyperplastic and adenomatous). Kudo et al. [29] confirmed the feasibility of applying the "pit patterns" of the colonic polyp to distinguish them via magnifying colonoscopy and indigo carmine dye contrast (Table 3) [28, 30].

Confocal Endoscopy

Today it is possible to obtain in vivo microscopic imagines by introducing a catheter into the operative

Table 3. Kudo et al classification for "pit pattern" [29]

Non neoplastic polyp Neoplastic polyp

Type I Normal round pit

Type II Small or large asteroid pit

Type III s Smaller than normal tubular or round pit

Type III l Larger than normal tubular or round pit

Type IV Dendritic or gyrous-like pit

Type V Nonstructural pit endoscopic channel [31, 32]. A fluorescent contrast agent is used to achieve high-contrast images. Fluorescein used systemically is preferred to acriflavine, tetracycline or cresyl violet used topically, since these agents have mutagenic potential cell's structure in a dedicated monitor. This new technology should allow histological diagnosis during conventional colonoscopy, but at the moment, accuracy is no better than 60%.

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