Uncommon tumours in the adult bladder: rare entities with recognized diagnostic pitfalls

Non-urothelial neoplasms and masses in the bladder such as myofibroblastic and smooth muscle proliferations, paraganglioma and lymphoma are uncommon. Nonetheless, pathologists must correctly classify these lesions to ensure optimal patient management. It is also recognized that particular entities in each of the aforementioned categories can be misconstrued as urothelial carcinoma or a spindle cell variant of urothelial carcinoma. This review will cover the clinicopathological features of selected lesions in the adult bladder including; myofibroblastic proliferations (occurring with antecedent trauma or spontaneously), smooth muscle neoplasms, sarcomatoid carcinoma, paraganglioma and lymphoma. The morphologic, immunohistochemical and, where appropriate, molecular/cytogenetic features described herein should help pathologists correctly classify these uncommon lesions.