Serrated polyps of the colon and rectum: Endoscopic features including image enhanced endoscopy

Abstract

In this review, I outline the characteristic endoscopic findings of serrated lesions of the colorectum based on image enhanced endoscopy (IEE). Histopathologically, lesions with serrated structures are typically classified into the following three types based: hyperplastic polyps (HPs), traditional serrated adenomas (TSAs), and sessile serrated adenoma/polyps (SSA/Ps). Both HP and SSA/P often present as dark-green colors on auto fluorescence imaging (AFI) colonoscopy that are similar to the normal surrounding mucosa. In contrast, TSAs often have elevated shapes and present as magenta colors that are similar to the tubular adenomas. The superficial type of TSA also includes many lesions that present as magenta colors. When SSA/Ps are associated with cytological dysplasia, many lesions present with magenta colors, whereas lesions that are not associated with cytological dysplasia present with dark-green colors. When observed via narrow band imaging (NBI), many SSA/P include lesions with strong mucous adhesions. Because these lesions are observed with reddish mucous adhesions, we refer to them as “red cap sign” and place such signs among the typical findings of SSA/P. Because the dilatation of the pit in SSA/P is observed as a round/oval black dot on magnified observations, we refer to this finding as II-dilatation pit (II-D pit) and also positioned it as a characteristic finding of SSA/P. In contrast, dilatations of the capillary vessels surrounding the glands, such as those that occur in tubular adenoma, are not considered to be useful for differentiating HPs from SSA/Ps. However, in cases in which SSA/P is associated with cytological dysplasia, the dilatation of capillary vessels is observed in the same area. When submucosal layer invasion occurs in the same area, the blood flow presents with irregularities that are similar to those of common colorectal cancer at an early stage and disappears as the invasion proceeds deeply. The surface pattern of invasive cancer that is observed at the tumor surface is also likely to disappear. Based on the above results, we considered that the differentiations between HP and TSA, between TSA and SSA/P, and between HP and SSA/P might become easier due to the concomitant use of white light observation and IEE. We also concluded that AFI and NBI can be useful modalities for SSA/P lesions associated with cytological dysplasia.

Keywords: Image enhanced endoscopy, Hyperplastic polyp, Early colon cancer, Traditional serrated adenoma, Sessile serrated adenoma/polyp

Core tip: Histopathologically, “serrated lesions” are categorized by the World Health Organization into three groups: (1) hyperplastic polyp; (2) traditional serrated adenoma; and (3) sessile serrated adenoma/polyp (SSA/P). I have discussed the findings associated with each lesion type as observed on image enhanced endoscopy. Regarding HPs and SSA/Ps, it is easy to differentiate both lesions. Especially, dilatations of the gland orifices are frequently observed in SSA/P and appear as blackish dotted orifices. And a thick mucous adhesion referred to as a “mucous cap” can be confirmed as red mucus on narrow band imaging observation and can be recognized when it adheres to the surface of a “red cap” polyp in SSA/P.