Oncocytoma

ONCOCYTOMA

• These are benign neoplasms that are composed of cells with abundant granular acidophilic cytoplasm, reflecting the presence of abundant mitochondri
• The etiology of oncocytoma is obscure, but immunohistochemical evidence suggests that these neoplasms are differentiating towards the intercalated cells of collecting ducts.
• Oncocytomas account for 3% to 5% of kidney tumors in adults
• Majority occurs in adults over age 50, with a reported age range of 10 to 94 years
• Men predominate over women in a ratio of 2-3 to 1

• These tumors are solitary well circumscribed, homogenous, mahogany coloured and have central stellate scar.
• Tumors vary in size from 2 -6cms

• Tumor cells are arranged in nests, tubular, trabecular and microcystic patterns.
• The cells of oncocytoma are round to oval but may appear columnar. Their cytoplasm is homogenous, acidophilic and granular in usual histologic preparation
• Focal vacuolization, representing intracytoplasmic lumens, occasionally occur
• Extracellular hyaline, reminiscent of basement membrane has been observed. Intracellular hyaline is not a feature of renal oncocytoma.
• Cytoplasmic lipochrome can be highlighted by stains for phosphotungstic acid and Sudan Black B.
• Central scar of an oncocytoma comprises collagenous tissue that may contain cystic area and even hemorrhage.
• Cells with pleomorphic and even bizarre nuclei occur singly or in aggregates. These nuclei lack both large nucleoli and mitosis and most authorities consider them as degenerative phenomenon.