Villous morphology in urinary bladder biopsy is a relatively uncommon finding. Villi are slender, finger-like structures that are commonly seen in the small intestine or in neoplastic lesions of gastrointestinal lineage/differentiation. Importantly, placenta also exhibits villi that are morphologically and functionally different from the intestinal one. Majority of the neoplastic lesions of urinary bladder are urothelial in origin with a minor subset showing glandular differentiation. While the presence of benign villi in urinary bladder biopsy necessitates a search for an occult perforation, provided a sample mismatch is ruled out, cytoarchitecturally abnormal/dysplastic villi indicate a neoplastic lesion of the urinary bladder encompassing villous adenoma and adenocarcinoma and urothelial carcinoma with villoglandular differentiation. The dysplastic villi in urinary bladder also imply a lower gastrointestinal endoscopy to rule out a colorectal primary. The development of the villous lesions in the urinary bladder and the colorectum are embryologically related and pose a major diagnostic challenge to the clinicians and surgical pathologists due to identical histomorphology and immunohistochemistry. We tend to discuss the morphological differentials and diagnostic approach to the villous lesions in the urinary bladder biopsy.
Villous adenoma of the urinary bladder: rare location