Mucinous adenocarcinoma of the rectum masquerading as inflammatory bowel disease-a case report.

The diagnosis of mucinous adenocarcinoma (MAC) is often challenging, particularly when it is confused with other entities such as inflammatory bowel disease (IBD) or benign pathologies. In this case, a 69-year-old woman presented with chronic constipation and was initially diagnosed with IBD after multiple institutions being consulted for her chronic symptoms. After experimental treatment with mesalazine for 6 months without improvement, she sought further consultation at our hospital. In cases of smooth surfaced mass with circumscribed projections in the rectal lumen, MAC should be considered as a potential diagnosis. To differentiate this entity from other pathologic entities, high sensitivity analysis is necessary for accurate classification. In ambiguous histopathological findings, implementing multi-point sampling strategies combined with targeted deep sampling at critical anatomical landmarks can significantly enhance diagnostic accuracy and facilitate a more comprehensive pathobiological evaluation of the disease. Highlights: 1) We identified a distinct presentation of rectal mucinous adenocarcinoma.2) When evaluating rectal masses resembling inflammatory bowel disease with inconclusive histopathological findings, in addition to employing the conventional multi-point sampling approach, targeted deep biopsies at critical anatomical landmarks can substantially enhance diagnostic accuracy.