PMC6358323_01
(A and B) Axial and sagittal computer tomography scans showing a large tumor with calcifications in the retroperitoneum. (C and D) Positron emission tomography-computed tomography scans showing focal activity in the lung, concern for metastatic disease (at the intersection).
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F1
A computed tomography (CT) scan of the abdomen confirmed a large solid, partly calcified mass in the left retroperitoneum with the lumbar muscle infiltrated and closely related to the abdominal aorta (Fig. 1A and B). The nuclear bone scan was normal. 18F-fluorodeoxyglucose Positron emission tomography-computed tomography (PET-CT) for the whole body shows that the glucose metabolism is slightly higher in the right lower lung and a metastatic tumor is considered to be present (Fig. 1C and D).
(A) Gross features of the large tumor (21 cm x 18 cm x 11 cm) replacing the kidney entirely. (B) The hemisection shows yellow-brownish, rock-hard masses with areas of hemorrhage and necrosis.
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F2
After gross examination, the kidney revealed a 21-cm  18-cm x 11-cm large tumor replacing the kidney (Fig. 2A). The surface cut showed central yellow-brownish, rock-hard masses with areas of hemorrhage and necrosis (Fig. 2B).
(A and B) Hematoxylin-eosin staining (100x) shows focal necrosis, spindle cells, and focal areas containing osteoid.
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F3
Microscopic examination of the hematoxylin-eosin stain demonstrated a diffuse arrangement of different sizes of spindle cell proliferation with interspersed osteoid of variable calcification (Fig. 3A and B).