Mesoblastic Nephroma of Adulthood

ABSTRACT

Mesoblastic nephroma is a benign neoplasm of the kidney, which is usually diagnosed during the first six months of life. Incidence in adults is exceedingly rare. We report herein a case of mesoblastic nephroma that occurred in the upper pole of the right kidney of a 39-year-old woman. It was a round mass measuring 3X3X2 cm in dimension. Microscopically, it consisted of uniform spindle cells with foci of hyalinization and dystrophic calcification. Tubular structures were entrapped in the tumor. Upon immunohistochemical staining, the spindle cells were found to be positive for smooth muscle actin, desmin, and vimentin. The epithelial cells of the entrapped tubules were positive for cytokeratin. On electron microscopic examination, the spindle cells demonstrated smooth muscle differentiation identified by indented nuclei, microfilaments beneath the cell membrane, dense bodies, and basal lamina-like materials.