Case report: intra-renal paraganglioma masquerading as a renal cyst.

A case is reported in which a 46-year-old normotensive male patient presented with large right-sided painless abdominal mass. On sonography there was a large cyst in the lower pole of right kidney. Intravenous urography showed distortion of pelvicollecting system and medial shift of upper right ureter. Exploration revealed a cystic mass (18 x 15 cm) located in lower pole of right kidney. It contained brownish fluid and because of suspicion of malignancy radical nephrectomy was carried out. Histological examination showed the cystic mass to be adrenal tissue infiltrated by neoplastic cells. Characteristic organoid nests of malignant cells ("Zellaballen" were present. Cells stained positively for chromogranin, neurone specific enolase (NSE), neurofilament, and synaptophysin. Sustentacular cells showed positive reaction to S-100 protein. No further treatment was offered. Patient remains well at 30 months follow-up. On medline search there is record of three cases of intra-renal paraganglioma in English literature and the present case appears to be the fourth one.