**2. Detection of colorectal neoplasms using colonoscopy**

It is generally known that conventional colonoscopy fails to detect some colorectal neoplasms (Rex, et al., 1997) and that such failure may lead to interval cancers between successive colonoscopies. To date, many attempts have been made to improve screening and surveillance colonoscopy. Mounting a transparent hood (TH) on the tip of the colonoscope helps in the detection of colorectal neoplasms by pressing and flattening the colonic folds, thus improving the endoscopic view (Hewett & Rex, 2010). On the other hand IEE, including the total colonic dye-spray method, narrow-band imaging (NBI), flexible spectral imaging color enhancement (FICE) and autofluorescence imaging (AFI) offers the possibility of increasing the detection rate of colorectal neoplasms by increasing the visibility of colorectal neoplasms.

Although the reasons for overlooking colorectal neoplasms are unknown, there are two major possibilities (Fig. 1). One is that the overlooked lesions are small and hidden behind colonic folds. Endoscopists should check possible blind spots by using 'mechanical' devices which allow them to look behind colonic folds. The other possible reason is that the overlooked lesions are flat and similar in color to the surrounding mucosa, which makes

Recent Advances in Diagnostic Endoscopy for Colorectal Neoplasm 213

that the TH reduced the miss rate for polyps from 15% to 0%. In their randomized tandem colonoscopy study, Hewett & Rex also reported that cap-fitted colonoscopy reduced the miss rates for all adenomas, and specifically for small adenomas (Hewett & Rex, 2010).

Fig. 2. (A) Transparent hood (TH, D-201 series; Olympus Medical Systems, Tokyo, Japan). (B) The TH attached to the tip of the colonoscope. (C) The endoscopic view of the cap-fitted

Image-enhanced endoscopy is expected to be better at detecting adenomas than conventional white light imaging (WLI). There are two types of IEE: dye-based and equipment-based (Kaltenbach, et al., 2008). In dye-based IEE, absorptive or contrast dye is used to enhance the features of the lesion. The typical absorptive dye for colonoscopy is crystal violet and the typical contrast dye indigo carmine. Indigo carmine, which can provide enhancement of the details of lesions by highlighting subtle changes in mucosal topography, is usually used to minimize the overlooking of colorectal neoplasms. On the other hand, there are a number of categories of equipment-based IEE. These include optical method such as NBI, electronic methods such as FICE, and optical-digital methods such as

colonoscope. The tip of TH is seen on the right edge of the endoscopic view

AFI.

**2.2 Optical methods for minimizing the overlooking of colorectal neoplasms** 

them difficult to recognize using conventional white light endoscopy. Some type of 'optical' image enhancing device should be used for detection of this type of lesion. Therefore, endoscopists should utilize both 'mechanical' and 'optical' devices to minimize the overlooking of colorectal neoplasms.

Fig. 1. Possible reasons for overlooking colorectal lesions. A tortuous lumen with colonic folds can result in the overlooking of small lesion behind the folds. Flat lesions of a similar color to the surrounding mucosa can also be easily overlooked

### **2.1 Mechanical methods for minimizing the overlooking of colorectal neoplasm**

Some mechanical methods for minimizing the overlooking of colorectal neoplasms have been proposed. One of them is the Third Eye Retroscope, which is passed through the working channel of a standard colonoscope and provides retrograde visualization of the colon (Triadafilopoulos, et al., 2007). In a multicenter randomized controlled trial, it resulted in the diagnosis of about 50% additional adenomas (Leufkens, et al., 2011). The other is the Aer-O-Scope, which provides simultaneous 360° viewing of the mucosal surface of the colon. The use of this device was reported in a preliminary pilot feasibility study (Vucelic, et al., 2006). Although both are promising devices that allow direct visualization of the back of colonic folds, they require an additional endoscope or endoscopic system and are much too complicated technically. Therefore, they have not become standard methods for screening colonoscopy.

Cap-fitted colonoscopy uses a TH affixed to the colonoscope tip (Fig. 2). It flattens the colorectal folds and improves mucosal exposure. The method is very simple and requires only a TH, which costs about \$20. The efficacy of THs has been reported previously (Matsushita et al., 1998). They performed tandem colonoscopy on 24 patients and proved

them difficult to recognize using conventional white light endoscopy. Some type of 'optical' image enhancing device should be used for detection of this type of lesion. Therefore, endoscopists should utilize both 'mechanical' and 'optical' devices to minimize the

Fig. 1. Possible reasons for overlooking colorectal lesions. A tortuous lumen with colonic folds can result in the overlooking of small lesion behind the folds. Flat lesions of a similar

**2.1 Mechanical methods for minimizing the overlooking of colorectal neoplasm**  Some mechanical methods for minimizing the overlooking of colorectal neoplasms have been proposed. One of them is the Third Eye Retroscope, which is passed through the working channel of a standard colonoscope and provides retrograde visualization of the colon (Triadafilopoulos, et al., 2007). In a multicenter randomized controlled trial, it resulted in the diagnosis of about 50% additional adenomas (Leufkens, et al., 2011). The other is the Aer-O-Scope, which provides simultaneous 360° viewing of the mucosal surface of the colon. The use of this device was reported in a preliminary pilot feasibility study (Vucelic, et al., 2006). Although both are promising devices that allow direct visualization of the back of colonic folds, they require an additional endoscope or endoscopic system and are much too complicated technically. Therefore, they have not become standard methods for screening

Cap-fitted colonoscopy uses a TH affixed to the colonoscope tip (Fig. 2). It flattens the colorectal folds and improves mucosal exposure. The method is very simple and requires only a TH, which costs about \$20. The efficacy of THs has been reported previously (Matsushita et al., 1998). They performed tandem colonoscopy on 24 patients and proved

color to the surrounding mucosa can also be easily overlooked

colonoscopy.

overlooking of colorectal neoplasms.

that the TH reduced the miss rate for polyps from 15% to 0%. In their randomized tandem colonoscopy study, Hewett & Rex also reported that cap-fitted colonoscopy reduced the miss rates for all adenomas, and specifically for small adenomas (Hewett & Rex, 2010).

Fig. 2. (A) Transparent hood (TH, D-201 series; Olympus Medical Systems, Tokyo, Japan). (B) The TH attached to the tip of the colonoscope. (C) The endoscopic view of the cap-fitted colonoscope. The tip of TH is seen on the right edge of the endoscopic view
