Rare entities in urinary bladder pathology.

Bladder carcinoma with variant histology is a subject of recent interest, with data suggesting more aggressive behavior when compared with conventional urothelial carcinoma. The timely identification and recognition of these histological variants should avoid their misinterpretation as benign lesions. We emphasize the need to recognize these peculiar morphologic features since some of them may require a different/specific therapeutic approach. Other rare entities such as bladder polyps and myofibroblastic proliferations tend to occur at a younger age and represent specific problems in the differential diagnosis. We describe the salient clinicopathologic features of representative rare entities arising in the urinary bladder.