Endoscopy 2007; 39(10): 920-921
DOI: 10.1055/s-2007-966846
Letters to the editor

© Georg Thieme Verlag KG Stuttgart · New York

Is acetic acid really effective as a mucolytic agent for magnifying colonoscopy diagnosis?

A.  Parra-Blanco, K.  I.  Fu, D.  Nicolás-Pérez, A.  Z.  Gimeno-García, M.  Carrillo, E.  Quintero
Further Information

Publication History

Publication Date:
29 October 2007 (online)

Magnifying colonoscopy can reliably predict histopathologic diagnosis, both for the neoplastic nature of lesions and the estimation of deep submucosal invasion [1]. Magnifying colonoscopy is applied with chromoendoscopy, either with contrast stains such as indigo carmine, absorption methods (methylene blue, crystal violet, cresyl violet), or more recently with digital chromoendoscopy such as the narrow band imaging (NBI) or the Fujinon Intelligent Chromoendoscopy (FICE) [2] [3]. Acetic acid has been used in digestive endoscopy mainly for the study of Barrett’s esophagus [4]. In a study recently published in Endoscopy, Togashi et al. [5] compared the accuracy of acetic acid plus indigo carmine either alone or in a combination to predict polyp histology. Acetic acid works as a mucolytic agent and, if not buffered by mucus, reversibly alters the tertiary structure of nuclear proteins in the epithelium [4]. Mucosal surface opacity is increased, decreasing the visibility of the capillaries and hence producing an increased contrast, with the mucosal surface appearing whitish.

In their interesting study, Togashi et al. [5] showed for the first time that acetic acid can be an alternative to indigo carmine, which is a very helpful tool for the endoscopist but presents several drawbacks, in particular that it is time consuming; moreover a covering of indigo carmine on the colonic mucosa could prevent the detection of other polyps if it could not be effectively removed after its application. Although acetic acid seems to be at least as good as indigo carmine for the examination of the pit patterns, the study did not clarify whether both agents were similar for the correct estimation of the polyp margin.

We have been using acetic acid for the study of colorectal polyps since we read this study, and have found it to be a very useful and practical agent when combined with magnification colonoscopy - its cleanliness being remarkable (as would be expected for a transparent agent) compared with indigo carmine. However, we would like to make two points. The first point is that we are not sure that the mucolytic effect of acetic acid is really effective, or effective enough to obviate the use of other agents (e. g. Pronase), which are usually used before the application of absorption stains such as crystal violet. We agree that acetic acid certainly enhances mucosal contrast, but probably in many polyps with abundant surface mucus (mainly hyperplastic polyps) the image obtained after acetic acid application may enhance the observation of the mucus covering the polyp. The second point we raise is that this persistence of mucus, despite the application of acetic acid, might also interfere with the observation of the capillary network during digital chromoendoscopy (NBI or FICE) in hyperplastic polyps, which in most cases are said not to exhibit any distinct vascular pattern.

Here we show a case of a 3 mm sessile polyp detected during screening colonoscopy. Histologic diagnosis could not be predicted by conventional observation, but after two applications of 1 % acetic acid plus magnification, a non-neoplastic crypt pattern was observed; no distinct vascular pattern was evident with FICE ([Fig. 1]), which is in keeping with the descriptions of NBI observation of hyperplastic polyps. Thereafter, 0.5 % indigo carmine was applied, with an unexpected effect of peeling off the mucus layer. Then, a distinct honeycomb vascular pattern was observed, tracing the shape of the hyperplastic-type crypt openings ([Fig. 2]).

Fig. 1 A sessile polyp 3 mm in diameter observed with the Fujinon Intelligent Chromoendoscopy (FICE) filter 4, after having applied acetic acid twice. A Kudo type II, Fujii non-neoplastic crypt pattern can be observed. No vascular pattern can be detected.

Fig. 2 Indigo carmine was applied after acetic acid. Unexpectedly, the mucus was peeled off. Repeat observation with FICE filter 4 provides a clear image of the honeycomb-type vascular pattern, which strongly suggests a hyperplastic polyp.

Acetic acid plus magnifying colonoscopy provides clear images for the differential diagnosis of colonic polyps, and it has several potential advantages over indigo carmine. However this case shows that the reported effect of acetic acid on mucolysis warrants further evaluation, and probably when we observe some polyps (mainly hyperplastic) after the application of acetic acid, we may still be observing just a more contrasted mucus layer.

Competing interests: None

References

  • 1 Kato S, Fujii T, Koba I. et al . Assessment of colorectal lesions using magnifying colonoscopy and mucosal dye spraying: can significant lesion be distinguished?.  Endoscopy. 2001;  33 306-310
  • 2 Machida H, Sano Y, Hamamoto Y. et al . Narrow band imaging in the diagnosis of colorectal lesions: a pilot study.  Endoscopy. 2004;  36 1094-1098
  • 3 Pohl J, May A, Rabenstein T. et al . Computed virtual chromoendoscopy: a new tool for enhancing tissue surface structures.  Endoscopy. 2007;  39 80-83
  • 4 Lambert R, Rey J F, Sankaranarayanan R. Magnification and chromoscopy with the acetic acid test.  Endoscopy. 2003;  35 437-445
  • 5 Togashi K, Hewett D G, Whitaker D A. et al . The use of acetic acid in magnification chromoendoscopy for pit pattern analysis of small polyps.  Endoscopy. 2006;  38 613-616

A. Parra-Blanco, MD

Unidad de Endoscopia

Hospital Universitario de Canarias

Ofra s/n, La Laguna

38320 Santa Cruz de Tenerife

Spain

Fax: +34-922-678 554

Email: parrablanco@gmail.com

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