Figure 2a: Incidental mass in interpolar region of left kidney in a 61-year-old man. (a) Transverse T1-weighted MR image (repetition time msec/echo time msec, 285/4.2) shows 2.5-cm mass (arrowhead) that enhanced homogeneously. CT-guided percutaneous biopsy was performed (not shown). (b) Photomicrograph of cytologic preparation reveals oncocytic cells (arrows). (Giemsa stain; original magnification, x600.) Immunocytochemical reaction for keratins AE1/AE3 (not shown) was positive. Hale colloidal iron stain (not shown) was negative. Diagnosis was renal oncocytoma.