Congenital Mesoblastic Nephroma Mixed Subtype: A Case Report of a Rare Neonatal Tumor.

Congenital renal tumors are rare. In infancy, congenital mesoblastic nephroma is the most commonly reported renal tumor. It is recognized antenatally due to polyhydramnios and presents clinically as a palpable abdominal mass in the neonatal period. Although widely regarded as a benign tumor, radical nephrectomy is routinely adopted as an effective treatment. We report a case involving antenatal recognition of a large fetal renal mass with polyhydramnios at 35 weeks of gestation. At 37 weeks of gestation, the baby was delivered via emergency cesarean section due to fetal distress. After delivery, a magnetic resonance imaging scan confirmed a solid mass in the left kidney, and a left radical nephrectomy was performed in the second week of life. The subsequent pathological examination confirmed a mixed (cellular and classical) variant of congenital mesoblastic nephroma.