Figure 7a: Incidental hyperattenuating mass in interpolar portion of right kidney in a 67-year-old woman. (a) Transverse unenhanced CT image shows 2.3-cm mass (arrowhead) with hyperattenuating (54-HU) areas within the mass and no evidence of fat. (b) Transverse CT image shows enhancement (77 HU) of the mass (arrowhead). (c) CT-guided percutaneous biopsy, shown on transverse CT image, was performed with a 25-gauge needle (arrow), with patient in prone position. (d) Photomicrograph reveals spindle cells (arrow). (Papanicolaou stain; original magnification, x400.) (e) Photomicrograph of cell block shows fat cells (arrow). (Hematoxylin-eosin stain; original magnification, x400.) (f, g) Photomicrographs of immunocytochemical-stained specimens are positive for (f) smooth muscle actin and (g) MART1 (melanoma antigen recognized by T cells), which are both demonstrated as brown areas. Diagnosis was an angiomyolipoma with minimal fat. (Original magnification for f and g,x400.)