Renin production in congenital mesoblastic nephroma in comparison with that in Wilms' tumor

The case of an infant with congenital mesoblastic nephroma and associated reninism is presented. The patient was a 39-day-old boy who presented with a left abdominal mass and mild hypertension (112/70 mm Hg). Both plasma renin activity (PRA) and plasma total renin concentration (PTRC) were elevated; the PTRC value of 1458 pg/mL of this case was the highest we had seen in patients with childhood renal tumors. The tumor was successfully removed and histologically confirmed as a congenital mesoblastic nephroma (cellular variant). The patient's PRA and PTRC returned to normal after nephrectomy. Indirect immunoperoxidase staining showed renin localized predominantly in the juxtaglomerular apparatuses adjacent to the glomeruli entrapped by the tumor. No positive staining was seen in the tumor cells. These findings indicate that the entrapped glomeruli may play a significant role in producing renin. More important, PTRC was extremely high compared to the moderate increase of PRA and to the mild elevation of blood pressure. The mechanism of renin production by childhood renal tumors is discussed, and the importance of studying inactive renin and total renin is emphasized.