Roel Bogie

General introduction

All inall, colonoscopy remains a safeprocedureand is currently themost appropriateexamination for the nation-wide CRC screening of the population in addition to fecal occult blood testing. By participating in the national CRC screening program, participants take a small procedure related risk in return for a significant risk reduction with respect to the development of CRC. This can only be achieved by complete visualization of the colonic mucosa and effective resection of premalignant neoplasms. To achieve this, quality benchmarks have been set, e.g.: adequate bowel preparation in ≥90% of all colonoscopies (Boston Bowel Preparation Scale [BBPS] ≥6, minimal 2 for each segment), cecal intubation rate in ≥90% of all colonoscopies, detection of ≥1 adenoma in ≥25% of patients, and withdrawal time of ≥6 minutes. 9 Use of the correct therapeutic intervention is also a benchmark (≥80% correct therapy) and is important for reducing the need of multiple interventions and for decreasing residual tumor and recurrence risk. However, the most effective treatment is dependent of the lesion (size and histological type). Level of difficulty increases with size. 10 Polyp classification In order to accurately diagnose CRNs and select the best therapeutic option, lesion characterization is the first step. CRNs can be subdivided based on size, shape, and histology. Size is an important predictor for the risk of submucosal invasion, residual tissue and recurrence and determines (in combination with shape) which endoscopic treatment is indicated. 11 CRNs can be diminutive (≤5 mm), small (6-10 mm) and large (≥10 mm). According to ESGE guidelines, lesions larger than 20 mm are considered as very large and are more difficult to resect en-bloc. 12 The Paris classification is used to characterize CRN shape ( Figure 1.1 ). CRNs can be divided into polypoid and non-polypoid based on the height of the lesion. Non-polypoid CRNs are defined as having a height of maximal half the diameter of the lesion. 13, 14 Polypoid CRNs can have a stalk (pedunculated) or a broad basis (sessile). Non-polypoid CRNs can be flat or depressed. 15 Histologically, CRNs can be subdivided into hyperplastic polyps, adenomas, sessile serrated lesions, traditional serrated adenomas and CRCs. 16 Adenomas consist of three types: tubular, villous and tubulovillous adenomas. Sessile serrated lesions occur with and without dysplasia. Serration is one of the levels for histological classification; hyperplastic polyps, sessile serrated lesions with and without dysplasia and traditional serrated adenoma belong to the group of serrated lesions, while adenomas arenon-serrated. Another level of classification isdysplasia; adenomas, traditional serrated adenomas, sessile serrated lesions with dysplasia and CRCs are considered as dysplastic, while hyperplastic polyps and sessile serrated lesions without dysplasia are considered as non-dysplastic.

1

Figure 1.1: Paris classification. | 0-I lesions are polypoid and 0-II and 0-III lesions are non-polypoid. Combinations are possible.

9