Congenital mesoblastic nephroma

Congenital mesoblastic nephroma (CMN), also known as fetal renal hamartoma or mesoblastic nephroma, is a rare kidney tumor that occurs predominantly in newborns and young infants. It is the most common renal tumor diagnosed in the first three months of life. The tumor arises from the mesenchymal (connective tissue) cells of the kidney and primarily affects the renal system. CMN can sometimes be detected prenatally by ultrasound, and it may be associated with polyhydramnios (excess amniotic fluid) during pregnancy. After birth, the most common presenting feature is a palpable abdominal mass, which may be accompanied by hematuria (blood in the urine), hypertension, and hypercalcemia in some cases. Histologically, CMN is classified into three subtypes: classic (resembling infantile fibromatosis), cellular (which shares features with infantile fibrosarcoma and frequently harbors the ETV6-NTRK3 gene fusion resulting from a t(12;15)(p13;q25) translocation), and mixed. The cellular variant tends to occur in slightly older infants and may carry a somewhat higher risk of local recurrence. The classic variant generally has an excellent prognosis. The primary treatment for congenital mesoblastic nephroma is complete surgical resection (nephrectomy), which is curative in the vast majority of cases. When the tumor is completely removed with clear surgical margins, the prognosis is excellent, with very high survival rates. Chemotherapy is generally reserved for rare cases with incomplete resection, recurrence, or metastatic disease, particularly in the cellular subtype. Long-term follow-up with imaging is recommended to monitor for recurrence, especially in the first year after surgery.

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