Juxtaglomerular cell tumor. An immunohistochemical, electron-microscopic, and in situ hybridization study.

We present a case of juxtaglomerular cell tumor (JCT) in a 10-year-old boy. The child suffered from severe hypertension that returned to normal following the tumor resection. The diagnosis of JCT was supported by electron-microscopic findings of typical rhomboid secretory granules and by immunohistochemistry using a polyclonal antibody against active and inactive forms of renin. The production of renin by the tumor cells was confirmed by demonstration of specific renin mRNA by in situ hybridization (ISH). The immunohistochemistry also showed a weak positivity of renin in the media of interlobular arteries and in the epithelial cells of proximal tubules. The ISH was negative for renin mRNA at these sites, indicating that renin positivity was due to an uptake of renin rather than to renin production. The juxtaglomerular apparatuses in the adjacent renal cortex were negative for renin, suggesting a compensatory inhibition mechanism by the hyperreninemia. The tumor was encapsulated by a fibrous tissue, but the capsule was penetrated by clusters of the tumor cells--an indication of the tumor's invasive capability.