Fat-forming solitary fibrous tumor of the kidney: a case report.

Background: Solitary fibrous tumor (SFT) arises in many parts of the body, but rarely in the kidney. To the best of our knowledge this is the second report of a fat-forming SFT in the kidney.

Case: We present a case of a fat-containing SFT at the parihilar region of the kidney in a 64-year-old man complaining of epigastric pain. The tumor was initially diagnosed as angiomyolipoma at hematoxylin and eosin stains. However, by immunohistochemistry the tumor was reclassified as a fat-forming SFT.

Conclusion: SFT arises in many sites, but rarely in the kidney. There is also a subset of these tumors that have a variable amount of adipocytic component that should be differentiated from angiomyolipoma. That subset of tumors affects mainly middle-aged adults of either gender and has a wide anatomic distribution. Recurrence is infrequent, and morphologically malignant examples are extremely rare.