A 31-year- old man with a clinical diagnosis of renal carcinoma underwent a wedge resection of kidney. At surgery, a circumscribed, soft, tan, hemorrhagic tumor was identified measuring 2.3 cm x 1.7 cm that bulged but did not appear to invade the capsule. The remaining renal parenchyma was grossly unremarkable. Representative cross-sections were submitted.

Sections revealed a well-circumscribed tumor consisting of cells arranged in nests, tubules, and cysts with an edematous stroma ( fig 1.1 HE 40X ). The cytoplasm was abundant, eosinophilic, and granular, and the nuclei were mainly round with conspicuous nucleoli ( fig 1.2 HE 200X ). Occasional bizarre nuclei were seen ( fig 1.3 HE 400X ). Prominent number of psammoma bodies were present in the stroma ( fig 1.4 HE 400X ). Tumor cells showed membranous immunoreactivity for CD117 ( fig 1.5 400X ). Hale’s colloidal iron stain was negative (fig 1.6 400X ).

• Chromophobe Renal Cell Carcinoma (fig 1.7 HE 400X ),
• Oncocytoma (fig 1.8 HE 100X ),
• Papillary Renal Cell Carcinoma (fig 1.9 HE 200X & HE 400X ), and
• Metanephric adenoma (fig 1.10 HE 200X & HE 400X ).

Oncocytoma with Psammoma bodies

Key Features:

• Benign renal epithelial neoplasm with a peak incidence of 65 years at presentation
• Often discovered incidentally by radiologic examination of the kidneys during workup for unrelated conditions
• Usually unilateral, solid, well circumbscribed but nonencapsulated round mass with pushing borders
• May have central stellate zones of white or pale gray stroma that connects with the periphery
• Composed of cells arranged in diffuse sheets or as cellular islands in a background of loose edematous stroma
• Tumor cells are round-to polygonal with densely granular eosinophilic cytoplasm; nuclei are mainly round with inconspicuous nucleoli. Occasional foci of “degenerative” nuclear atypia with pleomorphism may be observed
• Calcification, including psammoma bodies are uncommon; they are usually seen in association with either papillary areas or hemorrhage
• Negative Hale’s colloidal iron stain
• Mitotic figures, papillary architecture, clear or spindle cells, gross vascular invasion and gross extension into perirenal fat are almost never seen
• Overexpression of KIT (CD117) can be useful as an immunophenotypic marker
• Usually negative for cytokeratin 7
• Resection of the tumor is curative

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