[Intraepithelial neoplasia/dysplasia - histopathology in ulcerative colitis]

About 1-2% of all colorectal carcinomas (CRCs) arise from a background of chronic inflammatory bowel diseases (IBDs) such as ulcerative colitis (UC) or Crohn's disease, and around 15% of patients with IBD die from colorectal cancer. Intraepithelial neoplasia/dysplasia in the setting of IBD is considered a precancerous lesion by definition. Intraepithelial neoplasia may present itself either as a flat or polypoid mucosal lesion and is referred to as a dysplasia-associated lesion or mass (DALM) in the latter case. The therapeutic consequence of high-grade intraepithelial neoplasia/dysplasia and/or DALM is proctocolectomy in most centers because of the high risk of synchronous or metachronous CRC. The diagnosis of ulcerative colitis-related intraepithelial neoplasia and its distinction from regenerative changes and sporadic adenomas (ALMs) occurring in UC is still one of the greatest challenges in gastrointestinal pathology. Intra- and interobserver variability for the distinction between low-grade intraepithelial neoplasia and regenerative lesions tends to be quite high. This is partly due to the difficult histomorphology and partly due to the relative rareness of this diagnosis (approximately 10% of patients with IBD).