Chromoendoscopy technique uses a locally staining agent applied onto the
mucous membrane during the endoscopic examination to  improve tissue localization, characterization, or diagnosis during endoscopy. The method is cheap; the colouring agents are widely accessible and non-toxic.
The technique for staining is simple and easy to learn. The endoscope and catheter tip is directed toward the mucosa and a combination of rotational clockwise-counter clockwise movements is used to spray the mucosa through a catheter while simultaneously withdrawing the endoscope tip. Buscopan may help to minimize contractility and thereby facilitate staining.
The impact of chromoendoscopy on clinical outcomes relative to standard endoscopic and histologic methods has not yet been established in large controlled trials.
Currently used staining agents

  1. Indigo carmine-
    • It pools in crevices between epithelial cells thereby highlighting small or flat lesions and defining irregularities in mucosal architecture.
    • It is used to
    • To assist in detection of dysplastic changes in patients with ulcerative colitis undergoing surveillance colonoscopy.
    • To assist in detection of adenomas in patients with hereditary nonpolyposis colorectal cancer.
    • To diagnose small gastric cancers
    • Methylene blue
    • Methylene blue is absorbed by actively absorbing tissue like small and large intestinal epithelium, staining them blue. It does not stain nonabsorptive epithelium like squamous or gastric epithelium.
      The most extensive experience with methylene blue has been in the evaluation of Barrett’s oesophagus. Barrett’s oesophagus stains diffusely with methylene blue because of the specialised columnar epithelium. Dysplasia/carcinoma is associated with focal areas of decreased stain intensity and/or increased stain heterogeneity due to the differential absorption of methylene blue dye into dysplastic cells that have varying degrees of goblet cell loss. Thus, abnormal methylene blue staining is helpful in delineating dysplastic or malignant areas for diagnosis and endoscopic therapy, if needed.
      Recently concerns has been raised regarding the potential to induce oxidative damage to DNA (and hence accelerate carcinogenesis) in tissues exposed to methylene plus white light (such as during endoscopy).  However, this theoretical risk for increasing neoplastic transformation has not been proven by clinical studies.

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