Hydramnios associated with congenital mesoblastic nephroma: case report.

A case is reported of hydramnios due to excessive fetal urine production associated with congenital mesoblastic nephroma. Rapid growth of a right renal tumor and excessive fetal urine production were detected by measuring the size of the tumor and hourly fetal urine production during the development of hydramnios between 28-34 weeks of gestation. A female infant weighing 2200 g was born at 34 weeks' gestation. She lost 18% of her birth weight in the first 48 hours because of neonatal polyuria. Right nephrectomy and ureterectomy were performed 2 days after birth. After the operation, the neonatal polyuria improved dramatically. The right renal tumor was identified histologically as a mesoblastic nephroma. The importance is stressed of early and correct antenatal diagnosis of a renal tumor and precise estimation of urine production for postnatal management of hemodynamic change in cases of mesoblastic nephroma.