THE BASIC TECHNIQUE OF OBSERVATION OF COLORECTAL LESIONS BY MAGNIFYING ENDOSCOPY

Abstract

Endoscopic imaging methods have been divided into five categories by object-oriented classification. Narrow band imaging (NBI) is within the category of “Image-enhanced endoscopy”. A new system of NBI, the Lucera Elite^®, has stronger light power, enabling the endoscopist to observe details of colorectal lesions. In order to obtain clear images, it is important to wash out the covered mucous completely from the surface of the mucosa by using hot water.

With NBI, the imaging of mucosal microcapillary vessels and surface structure in the superficial layer of colon tumors can be emphasized. One of the benefits of NBI observation is that neoplasia can be easily recognized as a brownish area. According to JNET classification, colorectal lesions were classified into three types by Japanese NBI expert team with the shape of microcapillary vessels and surface structure on the surface of the tumor. Type 1 is defined as a sessile serrated lesion, especially a hyperplastic polyp. In contrast, type 3 is defined as submucosal deeply invasive cancer (SM cancer). Type 2 is divided into two subgroups, 2A and 2B. Type 2A includes mostly tubular adenomas and is an indication for endoscopic treatment, while type 2B includes intramucosal cancer and SM cancer. Further examination by using chromoendoscopy with magnification is necessary for colorectal lesions that are suspected to involve submucosal invasion.

Meanwhile, Kudo and Tsuruta pit pattern classification is commonly used in Japan. There are five types of pit patterns, type Ⅰ (one) to Ⅴ (five). Type Ⅰ is observed in normal colon mucosa. Type Ⅰ includes NET G1 (carcinoid tumor), malignant lymphoma and so on. Type Ⅱ is defined as a sessile serrated lesion, which is observed as star-shaped. Types Ⅲ to Ⅴ pit pattern are thought to have a neoplastic character. Type Ⅲ pit pattern is divided into two subtypes, Ⅲ_L and Ⅲs. Type Ⅲ_L includes typical common polyps and is observed as tubular adenoma on histological examination. In contrast, the Ⅲs pit is characteristic of depressed lesions, such as Ⅱc type, Type Ⅳ pit pattern is commonly observed in villous type tumors. Type Ⅴ pit is also divided into two subtypes. One is the Type Ⅴ_I (irregular) pit pattern and another is Ⅴ_N (non-structure) pit pattern. The Type Ⅴ_I pit pattern is observed in intramucosal cancers, tubular adenoma with high-grade dysplasia, or SM cancer. Therefore, it is necessary to carefully observe the details of pit pattern by using crystal violet staining. Type Ⅴ_N pit pattern is often observed in SM cancers with deep invasion. These lesions are an indication for surgical resection.

The relationship between conventional endoscopic observation and magnified endoscopic observation can be compared to two wheels of a bicycle. It is important to use both methods to increase the accuracy of pre-operative diagnosis of the depth of invasion and to develop a treatment strategy.