Usually appear as well-encapsulated tumors.

Grossly, the the tumor is usually small but may reach a large size (up to 12 cm) and has a gray-white to tan cut surface.

Microscopically, the tumor is made of large eosinophilic cytoplasm which contain a large number of mictochondria. These tumors should be differentiated from renal cell carcinoma which contain granular cells.