Minimum required resolution standard required for analysis of mucosal microvascular architecture at magnification endoscopy

We read with great interest the article written by Dr. Ohashi et al. [1]. They described how measurement of the calibre of microvessels can be used for distinguishing gastric cancer from benign lesions using image analysis. This quantitative analysis seems to be important for establishing the scientific methodology necessary for gastrointestinal endoscopy.

However, from the technical point of view, further discussion is warranted. In their study, they excluded 61 patients from among 132 patients, the only reason given being that “the analysis was not possible in the other 61 patients because the quality of the image was not good enough”. When we measured the maximum resolution power of a zoom scope which was identical to the one which they used, however, it was found to be 7.9 micrometres [2]. In the same report, we suggested that the magnification endoscopy technique had enough resolution power to dissect capillaries because the minimum diameter of the gastric capillary is 8 micrometres. Using this maximum resolution power of the scope, we showed that we were able to visualise the regular subepithelial capillary network within the noncancerous surrounding gastric mucosa in 100 % of cases in clinical practice [2]. Even though we did not measure the calibre of the capillaries, we were able to visualise irregular microvessels whose calibres were similar to or even smaller than those of the capillaries within the noncancerous surrounding mucosa as shown in Figure [1] [1] [2]. When we studied the figures in the paper by Ohashi et al. [1], we found that we were unable to recognise such minute microvascular architecture, i. e. vessels as small as capillaries. Ohashi et al. therefore seem to have sampled only rather large microvessels. If their resolution power had been high enough to visualise the more minute vessels, the mean calibre of the microvessels measured in both the malignant and the benign lesions of their subjects would have been different.

Figure 1 A magnified endoscopic image taken at the border of a histologically differentiated, depressed-type intramucosal gastric carcinoma. The arrows show a clear demarcation line, marking a border between the cancerous and the noncancerous mucosa. In the noncancerous mucosa (outside the demarcation line), subepithelial capillaries that are regular in size, shape, and arrangement are clearly and consistently visualised [2]. In contrast, microvessels that are distinctly irregular in size, shape, and arrangement and which have proliferated densely can be seen clearly within the cancerous mucosa. Although the calibre of each of the irregular microvessels within the cancerous mucosa is similar to or even smaller than that of the regular subepithelial capillaries within the surrounding noncancerous mucosa, these irregular microvessels can nevertheless be clearly seen.

Furthermore, in their histological study, measurements of the calibre of the microvessels were made in the section stained only with hematoxylin and eosin stain. It is quite difficult to detect microvessels using hematoxylin and eosin staining alone, especially in undifferentiated carcinoma, because such carcinomatous cells usually destroy or compress microvessels within the lamina propria as they proliferate during the early stage [4]. We consider that immunostaining specific for the endothelium is absolutely mandatory in order to measure the calibre of microvessels as small as capillaries, as reported in a previous study [4]. We conclude, therefore, that the calibre of the microvessels that Ohashi et al. were able to visualise may have been overestimated in their results.

There are numerous reports focusing on microvascular architecture as visualised by magnification endoscopy [5]. In order to carry out a scientific analysis, however, it is necessary for the researcher to state the minimum size of the vessel that can be visualised by their own magnification endoscopy technique before the analysis. We suggest that the analysis of microvascular architecture as visualised by magnification zoom endoscopy should be based on a technique that can consistently visualise vessels as small as the capillary, which is the smallest unit of the human vessels [6].

Competing interests: None

References

• 1 Ohashi Y, Niwa Y, Ohmiya N. et al . Quantitative analysis of the microvascular architecture observed on magnification endoscopy in cancerous and benign gastric lesions.  Endoscopy. 2005;  37 1215-1219
• 2 Yao K, Oishi T, Matsui T. et al . Novel magnified endoscopic findings of microvascular architecture in intramucosal gastric cancer.  Gastrointest Endosc. 2002;  56 279-284
• 3 Yao K, Iwashita A, Kikuchi Y. et al . Novel zoom endoscopy technique for visualizing the microvascular architecture in gastric mucosa.  Clin Gastroenterol Hepatol. 2005;  3 S23-S26
• 4 Furukawa K, Yao K, Iwashita A. et al . Microvascular architecture of depressed-type early gastric cancer: quantified vascular density using computer analysis with special reference to the color of endoscopic findings [in Japanese with English abstract].  Gastroenterol Endosc. 1997;  39 1358-1369
• 5 Yao K, Kida M. A review of current clinical applications of upper gastrointestinal zoom endoscopy.  Dig Endosc. 2005;  17 S2-S7
• 6 Yao K, Kato M, Fujisaki J. Techniques using the hemoglobin index for the gastric mucosa.  Endoscopy. 2005;  37 479-486