Primary malignant myopericytoma of the left atrium--a tumor of aggressive biological behavior: report of the first case and review of literature.

We report a case of malignant myopericytoma arising in the left atrium with brain, skeletal, and liver metastases, which, to our knowledge, is the first report of this rare entity in this anatomic location. A 52-year-old man presented with progressive blackening of his left field of vision. Magnetic resonance imaging and a computed tomography scan of the brain and thorax showed a heterogeneous mass in the right occipital lobe and a large left atrial floor mass. Excision of the atrial mass showed a circumscribed but unencapsulated malignant spindled neoplasm with a perivascular concentric cellular arrangement punctuated by sheets of tumor necrosis. The cells were round to spindled with eosinophilic cytoplasm and indistinct borders. Focally, the tumor infiltrated cardiac muscle. By immunohistochemistry, the cells were positive for smooth muscle actin and negative for desmin, H-Caldesmon, S-100, HMB-45, and Melan-A. The features were prototypic for malignant myopericytoma. Eight months after initial presentation, the patient is alive with metastatic disease.