Myoid differentiation in mesoblastic nephroma: clinicopathologic and cytogenetic findings of a rare case.

The authors report the case of a benign renal mesenchymal tumor in a baby boy detected by ultrasound scanning during prenatal diagnosis. Histologically, the tumor was diagnosed as a congenital mesoblastic nephroma (CMN) with myoid differentiation. The tumor normally is characterized by a fascicular proliferation of bland, spindle-shaped cells. CMN is the most common renal tumor in the neonatal period and presumedly results from a neoplastic transformation affecting the pluripotent mesodermal nephric blastema. In embryonic life, tumorigenic influences acting on the nephric blastema might result in selective overgrowth of its mesoblastic derivates. CMN must be differentiated from other spindle-shaped tumors, like Wilms' tumor, rhabdoid tumor of the kidney, clear cell sarcoma, nephrogenic adenofibroma, fibroma and fibrosarcoma, leiomyoma, metanephric stromal tumor, and, in this case especially, from tumors with myoid differentiation like infantile myofibromatosis. Numerical molecular abnormalities are observed frequently in renal mesenchymal tumors, especially in chromosome 11. Cytogenetic findings in our tumor after comparative genomic hybridization (CGH) showed full trisomies of chromosomes 20 and 22q, partial trisomies for the distal part of 11q and 1p, and an approximately full monosomy of chromosome 4 (4qter-4p15). The chromosomal imbalances of the tumor can be described as: rev ish enh(1p31pter,11q23qter,20,22), dim(4)(p15qter).