Malignant myopericytoma-like tumor in a Fischer rat.

Research paper by Naofumi N Takahashi, Toshinori T Yoshida, Yukiko Y Takeuchi, Maki M Kuwahara, Nobuaki N Nakashima, Yuko Y Chiba, Takanori T Harada

Indexed on: 24 Jul '08Published on: 24 Jul '08Published in: Toxicologic pathology


Myopericytoma is a perivascular tumor that has been recently described in humans, but not in laboratory rodents. The authors encountered an intra-abdominal tumor resembling human malignant myopericytoma in a Fischer rat. Grossly, the tumor was found as two brown-colored masses located in the mesentery of rectum. Microscopically, the tumor was composed of oval to spindle-shaped cells, which were arranged in sheets around numerous thin-walled branching vessels and partly showed a concentric perivascular growth pattern. Mitoses were frequently seen, and the tumor cells showed a local invasion. Immunohistochemically, the tumor cells were strongly positive for alpha-smooth muscle actin and weakly positive for vimentin and desmin. Ultrastructurally, the tumor cells had dendritic processes, actin-like thin filaments with dense bodies, basement membranes, hemidesmosomes, and micropinocytotic vesicles. These findings suggest that the most appropriate term for diagnosis of the present case could be a malignant myopericytoma.