Primary mesenchymal tumors of the urinary bladder. A histological and immunohistochemical study of 30 cases.

The light microscopic and immunohistochemical features of 30 primary mesenchymal neoplasms of the urinary bladder are reported. Half of the cases represented smooth and striated muscle tumors (five leiomyomas, seven leiomyosarcomas including epithelioid and myxoid subtypes, one rhabdomyoma, one embryonal rhabdomyosarcoma and one alveolar rhabdomyosarcoma). One third of the tumors were of fibrohistiocytic origin (one fibrous histiocytoma and eight malignant fibrous histiocytomas including fascicular and storiform, inflammatory and pleomorphic subtypes). In addition, a malignant epithelioid schwannoma, a round cell liposarcoma, two hemangiomas and two mixed mesodermal tumors were observed. The morphology of the vesical mesenchymal tumors was identical to that of their counterparts known to occur in other sites, particularly in the soft tissue. Muscle-specific actin, alpha-1-antichymotrypsin, S-100-protein and neuron-specific enolase proved to be useful and reliable immunomarkers for differential diagnosis of poorly differentiated leio- and rhabdomyosarcomas, malignant fibrous histiocytomas and malignant schwannomas. Since some tumors coexpressed several classes of intermediate filaments, diagnostic immunocytochemistry should only be used considering a larger panel of antibodies and in close correlation with the histological and cytological features of the neoplasms.