An Unusual Case of Synchronous Renal Cell Carcinoma in a Horseshoe Kidney and Intrahepatic Cholangiocarcinoma

We report an unusual FDG-PET/CT case of synchronous renal cell carcinoma of a horseshoe kidney and intrahepatic cholangiocarcinoma. A 70-year-old man presented with I day of frank hematuria, on a background of 4 months' treatment for polycythemia. CT identified the horseshoe kidney and isthmic tumor, with the renal lesion considered to be the primary neoplasm, and the hepatic lesion considered metastatic. FDG-PET/CT was performed to exclude further metastases. Histopathologic assessment revealed synchronous primary renal cell carcinoma (RCC) of the horseshoe kidney isthmus and intrahepatic cholangiocarcinoma. The polycythemia was attributed to a paraneoplastic effect of the RCC. Helpful factors in identifying synchronous primary tumors in this case were the absence of multiple metastases, and in more typical locations (bone for RCC; lymph nodes for cholangiocarcinoma) and the morphologic feature of minor capsular retraction adjacent to the liver lesion.