Renal Oncocytoma



Renal Oncocytoma


Satish K. Tickoo, MD

Victor E. Reuter, MD










Renal oncocytoma is typically well circumscribed with tan-brown cut surface. A central scar image is present in about 30% of the tumors. Such scars may also be seen in other low-grade slow-growing tumors.






The typical histologic features of renal oncocytoma include solid nests of cells with oncocytic cytoplasm and uniform, round nuclei, in a background of variable, but often loose, stroma.


TERMINOLOGY


Definitions



  • Benign, oncocytic renal neoplasms with prominent or exclusive nested architecture and uniform round nuclei


ETIOLOGY/PATHOGENESIS


Molecular Abnormalities



  • Loss of chromosomes Y and 1


  • Chromosome 11q13 alterations, including translocations



    • 11q13 alterations often involving CCDN1 gene, with overexpression of gene product cyclin-D1


  • Mitochondrial DNA (mtDNA) mutations, particularly with losses of genes for respiratory chain complex I


  • Many tumors with normal karyotype and no known FISH abnormalities


  • Rare familial cases described; later, many of these found to have Birt-Hogg-Dubé syndrome


CLINICAL ISSUES


Epidemiology



  • Incidence



    • 6-9% of renal tumors


  • Age



    • Mean: 62 years (range: 32-89 years)


  • Gender



    • M:F = 2:1


Presentation



  • Usually asymptomatic, detected on radiologic investigations for unrelated symptoms


Prognosis



  • Benign


MACROSCOPIC FEATURES


General Features



  • Well-circumscribed, nonencapsulated, usually solitary mass; sometimes multifocal (17%) and bilateral (4%)


  • Mahogany brown to yellow-tan color


  • Central stellate scar in up to 1/3 of cases; usually in larger tumors


  • Uncommon features: Gross cysts, extension into perinephric fat, or vascular invasion


Size



  • Mean: 4.4 cm (range: 0.6-15 cm)


MICROSCOPIC PATHOLOGY


Histologic Features



  • Architecture: Typically solid nests, but micro- and macrocysts or tubules also common



    • Closely packed nests sometimes imparting solid appearance


    • Nest separated by distinct reticulum framework


  • Cells with deeply eosinophilic, granular cytoplasm



    • Nuclei uniform and round, with vesicular chromatin and frequently prominent central nucleoli


    • Cytoplasmic clearing rare, usually restricted to areas of scarring


    • Sometimes cells at periphery of nests, “oncoblasts,” have scant cytoplasm


  • Occasional isolated or groups of cells with marked degenerative-appearing hyperchromasia and pleomorphism


  • Stroma hypocellular, often hyalinized


  • Some tumors with perinephric fat (20%) or vascular (5%) invasion


Predominant Pattern/Injury Type



  • Neoplastic



Predominant Cell/Compartment Type



  • Oncocytic


ANCILLARY TESTS


Immunohistochemistry



  • CD117 and Ksp-cadherin positive; CK7 usually negative to occasionally focal positive; claudin-7 negative or focal positive


Electron Microscopy



  • Round nucleus


  • Cytoplasm packed with mitochondria mostly showing lamellar cristae


DIFFERENTIAL DIAGNOSIS


Chromophobe RCC (Eosinophilic Variant)



  • Nuclear irregularities, with perinuclear halos; variety of growth patterns, including solid and broad alveoli


  • CK7 is often diffusely positive; microvesicles and mitochondria with tubulovesicular cristae on EM


Clear Cell RCC (Eosinophilic Variant)



  • Fine arborizing vascularity; nuclear atypia, chromatin irregularities


  • CA9 and CD10, diffuse membranous positivity


Epithelioid (Oncocytoma-like) Angiomyolipoma



  • Nuclear pleomorphism is common


  • Smooth muscle and adipose component


  • Melanocytic markers HMB-45 and Melan-A(MART-1) are positive

Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Renal Oncocytoma

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