Gregory Tsoucalas* and Aliki Fiska
Osseous metaplasia of the urinary bladder is a rarely found condition by pathologists during histological analysis. Cancer, infection and inflammation are implicated with its appearance. Our paper examines cases after 1991, excluding those with osseous metaplasia in distal visceral and/or nodal metastases and osteogenic malignancies like osteosarcomas. A series of 11 cases were found after a thorough search in PubMed and Google Scholar databases, while "bladder osseous metaplasia" and "bladder bone formation" were used as key search terms. Urothelial - transitional cell carcinomas are found to be involved in 81% of the cases, while one case of angiosarcoma and one case of leiomyosarcoma are included with a mean age of 70.7 years. Only 2 of the subjects were females. The theories for its appearance speculate a subclone of tumour cells able to induce osteogenesis, transformation of undifferentiated stromal mesenchymal cells into osteoblasts and bone morphogenetic proteins BMP-2 and BMP-Ib which act as cytokines. Osseous heterotopic metaplasia still constitutes a subject which needs further investigation.