[Congenital mesoblastic nephroma - a semimalignant fibroleiomyomatous kidney tumor of the newborn (author's transl)].

Abstract

The congenital mesoblastic nephroma is a distinct tumor entity, which should be clearly distinguished from Wilmus-tumor. The pure mesenchymal tumor is usually present at birth and palpated as a mass in the kidney. Macroscopically the tumor reveals a striking resemblance with an uterine fibroid. Histologically the tumor tissue ist characterized by 1. interlacing bundels of spindle cells with uniform cell nuclei and regular mitotic figures, 2. collagen fibres between the tumor cells, 3. an angiomatous marginal zone, no tumor capsule, 4. hematopoetic foci and dysplastic glomeruli and tubuli in areas where normal kidney parenchyma mixes with tumor tissue, 5. small myxomatous areas within in the tumor, 6. no invasion of blood vessels or pelvis. Prognosis of the congenital mesoblastic nephroma is much better than in Wilms-tumor. Metastases have not been described so far. If, however, the tumor tissue is incompletly removed during operation, the neoplasm may recur and prove fatal. Ultrastructural and DNA cytophotometric studies suggests a low grade malignancy rather than a truely benign behaviour of this tumor.