Colorectal Serrated Neoplasia: An Institutional 12-Year Review Highlights the Impact of a Screening Programme

Abstract

Background: As the malignant potential of sessile serrated lesions/polyps (SSL/Ps) and traditional serrated adenomas (TSAs) has been clearly demonstrated, it is important that serrated polyps are identified and correctly classified histologically.

Aim: Our aim was to characterize the clinicopathological features of a series of SSL/Ps & TSAs, to assess the accuracy of the pathological diagnosis, the incidence, and the rate of dysplasia in SSL/Ps & TSAs.

Methods: We identified all colorectal serrated polyps between 01/01/2004 and 31/05/2016, by searching the laboratory information system for all cases assigned a "serrated adenoma" SNOMED code. All available and suitable slides were reviewed by one pathologist, who was blinded to the original diagnosis and the site of the polyp. Subsequently discordant cases, SSL/Ps with dysplasia, and all TSAs were reviewed by a second pathologist.

Results: Over a 149-month period, 759 "serrated adenoma" polyps were identified, with 664 (from 523 patients) available for review. 41.1% were reviewed by both pathologists; 15.1% (100/664) were reclassified, with the majority being changed from SSL/P to hyperplastic polyp (HYP) (66/664; 9.9%). 80.3% of these HYPs were located in the left colon, and the majority exhibited prolapse effect. There were 520 SSL/Ps (92.2%) & 40 TSAs (7.1%). The majority of SSL/Ps were in the right colon (86.7%) and were small (64.5% <1 cm), while most TSAs were in the left colon (85.7%) and were large (73.1%≥1 cm). 6.7% of SSL/Ps exhibited dysplasia, the majority of which were large (66.7%≥1 cm). Following consensus review, 13/520 (2.5%) SSL/Ps were downgraded from SSL/P with dysplasia to SSL/P without dysplasia. Detection of SSL/Ps peaked in the most recent years reviewed (87.5% reported between 2013 and 2016, inclusive), coinciding with the introduction of "BowelScreen" (the Irish FIT-based colorectal cancer screening programme).

Conclusions: Awareness of, and adherence to, diagnostic criteria is essential for accurate classification of colorectal polyps.

Figure 1

Hyperplastic polyp, with prolapse effect, characterized by dilated and congested submucosal blood vessels, thickening of the muscularis mucosae, and upward extension from the hypertrophic and splayed muscularis mucosae, with dilated crypts (a, b). Horizontal extension of crypt bases along the muscularis mucosae can be seen, mimicking the architecturally distorted, dilated, and/or horizontally branched crypts of SSL/Ps (c, d).

Figure 2

Sessile serrated lesion/polyp (SSL/P) without dysplasia (a). SSL/P with low-grade conventional adenomatous dysplasia (b). SSL/P with low-grade serrated dysplasia (c). Traditional serrated adenoma (TSA) without dysplasia (d). TSA with low-grade conventional adenomatous dysplasia (e). TSA with serrated dysplasia (f).

Figure 3

The number of SSL/Ps detected between January 1^st 2004 and May 31^st 2016, with detection of SSL/Ps peaking in the most recent years included in this review (87.5% reported between 2013 & 2016, inclusive). This coincided with the introduction of “BowelScreen” (the Irish colorectal cancer screening programme).