Inflammatory bowel disease-associated colorectal dysplasia: the expanding morphologic landscape and diagnostic challenges.

Although most dysplastic lesions in inflammatory bowel disease (IBD) resemble sporadic adenomas, several less well-recognized morphologic variants have recently been described. These variants can be diagnostically challenging because of their subtle cytologic atypia and/or overlap with regenerative changes, often resulting in misclassification as benign, reactive, or indefinite for dysplasia. Furthermore, the use of different classification systems has led to inconsistent terminology and definitions across the literature and in clinical practice. Nevertheless, accurate recognition of these lesions is essential, as many are endoscopically invisible or flat and are associated with advanced neoplasia on follow-up, as well as synchronous and/or metachronous neoplasia, frequently arising within the same colonic segment. Accordingly, this review summarizes the evolution of the classification of IBD-associated dysplasia culminating in the 6th edition of the World Health Organization (WHO) Classification of Digestive System Tumours and discusses how the WHO framework relates to previously proposed classification systems. It further clarifies the terminology and diagnostic criteria of various dysplastic entities recognized in the WHO classification. In addition, the review presents a practical approach to the recognition and classification of these dysplastic variants and provides a standardized reporting framework to facilitate clinical management, including recommendations for lesions that exhibit partial histologic features but do not meet the criteria for a definitive diagnosis of dysplasia. Finally, the review provides an updated overview of the clinicopathologic features of these dysplastic variants and discusses ongoing controversies and unresolved questions in the field.