Benign perivascular myoid cell tumor (myopericytoma) of the urinary tract: a report of 2 cases with an emphasis on differential diagnosis.

Myopericytoma is a benign mesenchymal neoplasm thought to comprise part of a spectrum of perivascular myoid cell neoplasms with myofibroma, angioleiomyoma, and glomus tumor. We describe 2 such neoplasms involving the urinary tract: 1 incidentally identified in the kidney of a 59-year-old woman and 1 in the urinary bladder of a 52-year-old woman who presented with urinary frequency and dysuria. Histologically, the bladder tumor was composed of numerous blood vessels surrounded by plump perivascular myoid cells, as in subcutaneous myopericytoma. The renal tumor showed similar morphology centrally and a symplastic glomus tumor-like growth pattern at the periphery. Immunohistochemically, both tumors were reactive for markers of smooth muscle differentiation, such as smooth muscle actin and caldesmon/calponin but negative for CD34, cathepsin K, and S100 protein. Both patients are free of disease 14 and 39 months after resection, respectively. Our findings broaden the morphologic spectrum of myopericytoma.