Prenatal ultrasonographic diagnosis of fetal renal tumors.

An unusual case of a renal mesoblastic nephroma, diagnosed in utero, is presented. The tumor, which appeared as a solid mass in the region of the right renal bed on ultrasound, was composed of fibromyomatous tissue. It may be confused with Wilms tumor on sonography, but can be distinguished histologically, being composed of mesenchymal tissue, as opposed to the epithelial tissue of Wilms tumor.