Epithelioid hemangiosarcomas of the bovine urinary bladder: a histologic, immunohistochemical, and ultrastructural examination of four tumors.

Epithelioid hemangiosarcoma is a specific variant of hemangiosarcoma that has recently been recognized in domestic animals. These malignant vascular neoplasms histologically resemble, and may be mistaken for, carcinomas. Four epithelioid hemangiosarcomas in the urinary bladders of 4 cows with severe enzootic hematuria are described in the current study. Grossly, the vesicular mucosa of the urinary bladder of each cow contained a single red elevated nodule. Histologically, each neoplasm was composed of short strands, cords, or nests of epithelioid, round, or slightly spindle-shaped endothelial cells that formed small vascular structures. Neoplastic cells were immunohistochemically positive for factor VIII-related antigen and vimentin, and were negative for cytokeratin and desmin. Ultrastructurally, the neoplastic cells often contained cytoplasmic intermediate filaments, a prominent granular endoplasmic reticulum, a Golgi complex, mitochondria, marked pinocytotic activity, and rare Weibel-Palade bodies. These neoplasms were diagnosed as epithelioid hemangiosarcomas based on their histologic, immunohistochemical, and ultrastructural features. The present report widens the spectrum of mesenchymal tumors of the bovine urinary bladder and aids in the characterization of these vascular neoplasms.