Non-conventional dysplastic subtypes in inflammatory bowel disease: a review of their diagnostic characteristics and potential clinical implications

The early detection and grading of dysplasia is the current standard of care to minimize mortality from colorectal cancer (CRC) in patients with inflammatory bowel disease. With the development of advanced endoscopic resection techniques, colectomy is now reserved for patients with invisible/flat dysplasia (either high-grade [HGD] or multifocal low-grade dysplasia) or endoscopically unresectable lesions. Although most pathologists are familiar with the morphologic criteria of conventional (intestinal type) dysplasia, the most well-recognized form of dysplasia, an increasing number of diagnostic material has led to the recognition of several different morphologic patterns of epithelial dysplasia. The term “non-conventional” dysplasia has been coined to describe these changes, but to date, the recognition and full appreciation of these novel forms of dysplasia by practicing pathologists is uneven. The recognition of these non-conventional subtypes is becoming increasingly important, as some of them appear to have a higher risk of developing HGD or CRC than conventional dysplasia or sporadic adenomas. This review describes the morphologic characteristics of all seven non-conventional subtypes that have been reported to date as well as our current understanding of their clinicopathologic and molecular features that distinguish them from conventional dysplasia or sporadic adenomas.