Primary cardiac granular cell tumor in a dog

The histological, histochemical, and ultrastructural features of a granular cell tumor in the wall of the right atrium of the heart in a nine-year-old dog are described. The histologic appearance of the mass varied from areas of spindle-shaped cells to sheets of globoid cells with foamy granular cytoplasm. The globoid neoplastic cells contained numerous cytoplasmic granules which were variably positive to periodic acid-Schiff staining, with and without disastase digestion. Ultrastructurally, the globoid cells had numerous various-sized, heterogeneous lysosomes with pleomorphic content. A granular cell tumor originating in the heart has not been reported previously in animals. The support for a neural origin of these tumors by the recent identification of several nervous tissue specific proteins in their granular cells is discussed.