Acetic acid spray technique is effective for identifying adenomas covered with mucus

We appreciate the interest shown by Dr Fu and colleagues in our paper [1] on the use of acetic acid in magnification chromocolonoscopy for pit pattern analysis of small polyps.

Acetic acid is inexpensive and safe, and chemically the smallest fatty acid. This solution can eliminate the mucus layer and causes an aceto-white reaction in the mucosal layer. These interactions highlight the pit pattern image in magnification colonoscopy. Therefore, acetic acid spray is expected to be more effective for correctly identifying hyperplastic polyps in magnification chromocolonoscopy, because hyperplastic polyps are usually covered with thick mucus, as noted by Dr Fu and colleagues.

In our paper, however, acetic acid increased the accuracy of detection of adenomas (76 % to 94 %) more than that of hyperplastic polyps (92 % to 100 %). Acetic acid spray was therefore more effective for identifying adenomas. To understand these results, it is worth noting that most small adenomas are also covered with mucus, although the mucus covering such adenomas is not as much as that found on hyperplastic polyps. Mucus adhering to the surface of adenomas could be a confounding factor in magnification colonoscopy.

We would like to present a typical case from our paper, which was misidentified using indigo carmine spray, but correctly identified with acetic acid spray ([Fig. 1] and [2]). In [Fig. 1], an inadequate amount of indigo carmine attaches to the surface of the polyp owing to the mucus, thus leading to incorrect identification. After spraying with acetic acid ([Fig. 2]), a type IIIL pit is clearly identified, suggesting an adenoma. In comparison, the majority of hyperplastic polyps have thick mucus over their surface. We have found that it is not easy to completely eliminate this thick layer of mucus by spraying acetic acid. As a result, the acetic acid spray technique may not be as effective for identifying hyperplastic polyps. Indigo carmine spray might be sufficient to identify hyperplastic polyps, because the accuracy of hyperplastic polyp identification exceeded 90 % using indigo carmine spray alone.

Fig. 1 Polyp appearance after indigo carmine spray.

Fig. 2 Polyp appearance after acetic acid spray.

Dr Fu and colleagues draw attention to the diagnostic accuracy of indigo carmine spray with magnification in our paper, which was not as high as expected. Indeed, the diagnostic accuracy of magnification chromoendoscopy using indigo carmine was 95.6 % in Dr Fu and colleagues’ data [2], whereas it was 83 % in our data [1]. This discrepancy could be attributed to differences between study subjects and in the polyp prevalence observed in the two studies. Subject race, indications for colonoscopy, bowel preparation status and other factors were not the same in the two studies. Furthermore, the process of selecting study subjects was quite different. Dr Fu and colleagues excluded 605 of the 980 patients considered for the study because no polyps were detected. In contrast, we detected 73 polyps in 46 consecutive patients, with almost all patients having at least one polyp. We therefore contend that the higher polyp prevalence in our study argues against any selection bias which may have excluded smaller polyps, the histology of which might have been difficult to predict on magnification endoscopy. In previous studies [3] [4] [5] [6] [7] [8], the overall accuracy of magnification colonoscopy with indigo carmine ranged from 80 % to 92 %. Our results are therefore acceptable, whilst the overall accuracy (95.6 %) obtained in Dr Fu and colleagues’ study was remarkably high.

References

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