Urachal mucinous neoplasms--to be or not to be: Two cases and a review of current diagnostic criteria (WHO 2016)

The urachus is an embryological remnant that extends from the bladder to the umbilicus. Urachal neoplasms represent less than 1% of malignant bladder tumors. The new 2016 edition of disease classifications from the WHO has updated the classification of epithelial neoplasms of urachal origin, distinguishing between glandular and non-glandular neoplasms and between cystic and non-cystic adenocarcinomas. In this article, we present two cases with similar clinical presentations but differing histology. We address their morphological, immunohistochemical, and molecular characterization; review the classification and diagnostic criteria of glandular urachal neoplasms included in the most recent literature with the aim of clarifying their differential diagnosis as well as their prognostic implication; and, ultimately, better understand these infrequent biological entities.