Curriculum review: serrated lesions of the colorectum

Abstract

Colorectal cancer (CRC) is the second leading cause of death from cancer in the UK. Sporadic CRC evolves by the cumulative effect of genetic and epigenetic alterations. Typically, over the course of several years, this leads to the transformation of normal colonic epithelium to benign adenomatous polyp, low-grade to high-grade dysplasia and finally cancer-the adenoma-carcinoma sequence. Over the last decade, the serrated neoplasia pathway which progresses by methylation of tumour suppressing genes has been increasingly recognised as an important alternative pathway accounting for up to 30% of CRC cases. Endoscopists should be aware of the unique features of serrated lesions so that their early detection, appropriate resection and surveillance interval can be optimised.

Keywords: colorectal polyps; serrated polyps. word count – 2862.

Figure 1

The Joint Royal Colleges of Physicians Training Board 2010 gastroenterology curriculum—competencies for colorectal tumours.

Figure 2

Summary of features characterising the three subtypes of serrated lesions. images adapted from Ishigooka et al and Snover.

Figure 3

Two SSLs with dysplasia viewed under white light (left) and narrow-band imaging (NBI) (right). Top: flat elevated lesion (Paris IIa) with clouded surface. Bottom: flat elevated lesion with sessile component (Paris IIa +Is) and indistinctive border. The dysplastic portions (red box) appear darker under NBI with Kudo type III–IV pits.

Figure 4

The WASP classification for optical diagnosis of hyperplastic polyps, sessile serrated lesions and adenomas based on the NBI International Colorectal Endoscopic criteria and the Hazewinkel criteria in a stepwise approach.

Figure 5

2017BSG algorithm for serrated lesion surveillance. Diminutive (<5 mm) HPs in the rectosigmoid are not thought to be risk markers for future CRC. It is currently unclear whether proximal small HPS or SSLs are markers for future CRC risk. CRC, colorectal carcinoma; HP, hyperplastic polyp; SSL, sessile serrated lesion.