Metanephric Adenoma of the Kidney

ABSTRACT

Metanephric adenoma is a rare renal epithelial tumor. Its light microscopic features are very characteristic, and immunohistochemical and electron microscopic studies are not critical to the diagnosis. The literature indicate that, to date, the tumor has behaved in a benign fashion, and predominantly but not exclusively occurred in middle-aged women. It occurs in a wide range up to 11 cm and is usually an incidental finding but may be symptomatic with hematuria or flank pain. Recently, we have experienced a case of renal tumor showing distinctive adenomatous features, which is incidentally found in a 52-year-old female. This tumor is confined to the renal cortex and is well-circumscribed with a characteristic uniform and orderly proliferation of compact well-differentiated small tubules lined by bland oval cells with a very low level of mitotic activity. The term metanephric adenoma is appropriate for this tumor because it accurately describes its bland proliferation of tubules and reflects the embryonic architectural and cytological appearance of this proliferation. The pattern of the tumor, with its occasional papillary glomeruloid- like bodies and foci of elongated tubules, is reminiscent of the fetal metanephric kidney.