A morphologic reappraisal of endoscopically but not histologically apparent polyps and the emergence of the overlooked goblet cell--rich hyperplastic polyp

An update on the morphology and molecular pathology of serrated colorectal polyps and associated carcinomas

Our understanding of serrated colorectal polyps has increased dramatically over the past two decades and has led to a modern classification scheme for these lesions. Sessile serrated polyps with dysplasia represent the most clinically significant serrated polyp; however, the morphologic heterogeneity of dysplasia in sessile serrated polyps has only recently been recognized and correlated with MLH1 immunohistochemistry. Detailed morphologic analysis of traditional serrated adenomas has led to the recognition of flat and early forms of this polyp. Robust data on the risk of metachronous lesions in patients with serrated polyps are also beginning to emerge. This review will summarize our current understanding of serrated polyps and associated carcinomas with a focus on diagnostic criteria, morphologic heterogeneity, molecular findings, and natural history. Controversial issues in the diagnosis and classification of these polyps are also discussed.

Colonic Mucosa With Polypoid Hyperplasia

OBJECTIVES

Define the morphologic and molecular features of colonic polyps with subtle histologic features.

METHODS

Two hundred specimens were obtained of surveillance colonoscopies. Endoscopic findings were reviewed. Histologic features of the polyps were compared with the flat mucosa. Next-generation sequencing was performed on 30 study polyps and 20 control samples.

RESULTS

Polyps with subtle changes comprised 12% of all polyps. All polyps were sessile and small (<0.5 cm) and were located predominantly in the distal colon (60%). Synchronous hyperplastic, sessile serrated, and dysplastic polyps were found in 30%, 7%, and 51% of patients, respectively. A total of 169 (84.5%) polyps showed wide, nonserrated crypts, increased intraluminal mucus, and patent openings. KRAS alterations were present in 30% of polyps.

CONCLUSIONS

Most polyps with subtle histologic features have recognizable morphologic changes. About one-third harbored KRAS alterations. These polyps should not be regarded as variants of hyperplastic polyps.