Abstract
Since a myxomatous white mass (8×5×4mm) was grossly observed postmortem in the right ventriclar epicardium of rat F344 which was 106 weeks old, a histopathological examination was conducted. Histologically, there were two different areas. One consisted of spindle-shaped tumor cells, which were arranged in a herring bone pattern, interlacing bundlle pattern, whorl pattern and nuclear palisading (Antoni type A). The other consisted of small round tumor cells, which showed myxomatous proliferation and cyst formation (Antoni type B). These tumor cells were diagnosed as malignant schwannoma by positive immunoreactivity to S-100 protein antigen in the cytoplasm and nuclei, and ultrastructual features of circumferential basal lamina. This case is interesting in that the large tumor which originated in the right ventricle, proliferated extrusively from ventricle to epicardium, and tested strongly positive for S-100 protein antigen in an immunohistochemical staining procedure.
