Figure 1. Gross specimen of the right kidney: cut section of the kidney showing a heterogenous tumor showing grey white homogenous area with whorling pattern (black arrow) and areas of necrosis and hemorrhage (red arrow).
Microscopically, the tumor was composed of spindle-shaped cells arranged in interlacing fascicles, bundles, and whorls (Figure 2). The tumor cells were moderately pleomorphic with a moderate amount of eosinophilic cytoplasm, oval to elongated nuclei, vesicular chromatin, and inconspicuous nucleoli. Mitotic figures were frequent, constituting a 19/10 high power field. Large areas of necrosis and hemorrhage were noted. The mass involved the renal sinus and perirenal fat, however, Gerota’s fascia was free of tumor. The lymphovascular invasion was noted. Extensive sampling failed to reveal any epithelial component resembling renal cell carcinoma. Microscopic examination of the inferior vena cava thrombus revealed a tumor with similar morphology as in the kidney.