Head of department of urology Imland Hospital Rendsburg Rendsburg, Germany
Background: The rare benign tumors of the kidney comprise a group of histogenetically very different entities. After extensive literature research, the metanephric adenoma is one of the rarest tumor entities of the kidney.
Methods: Initially, a 53-year-old patient presented to her family doctor with slight pain in her right flank. There was neither hematuria nor dysuria. All laboratory parameters were within the normal range. The sonography revealed an approximately 4.5 cm inhomogeneous mass at the upper pole of the right kidney which was confirmed by MRI. A right-sided nephrectomy was then performed laparoscopically.
Results: Histologically, no malignancy criteria were found in the tumor surrounded by a pseudocapsule, no tumor penetration into branches of the renal veins and no infiltration of the perirenal fatty tissue. The resection margins were all tumor-free. In immunohistochemistry, CD10 and cytokeratin 7 were negative. WT-1 showed low to moderate nuclear positivity in 70% of the tumor cell population. The proliferation marker MIB1 (Ki-67) was < 1%. In summary of these findings, the diagnosis of a benign metanephric adenoma of the kidney was made histologically/immunohistochemically.
Conclusions: With less than 200 documented cases in the literature, the metanephric adenoma described here is a rarity in everyday urological practice and cannot be distinguished from a malignant tumor of the kidney clinically and/or by imaging without histological assessment. The clinical symptoms of metanephric adenoma are very variable and non-specific. Flank pain, hematuria, or a palpable tumor can be early signs. 10% to 20% of patients have polycythemia, which is reversible after tumor resection. Most metanephric adenomas occur in adults aged 50-60 years, the median age is 41 years (5-83 years). The ratio of women to men is 2:1. With regard to clinic, age and gender, as well as the described histopathology, our case seems to fit into the typical representative cases.