Kidney tumor
Benign adult tumors

Topic Completed: 1 February 2012

Minor changes: 26 May 2020

Copyright: 2003-2019,, Inc.

PubMed Search: Oncocytoma [title] kidney

Mandolin S. Ziadie, M.D.
Page views in 2019: 26,567
Page views in 2020 to date: 13,548
Cite this page: Ziadie MS. Oncocytoma. website. Accessed July 4th, 2020.
Definition / general
  • Benign tumor of uniform round / polygonal cells with abundant, intensely eosinophilic and granular cytoplasm with uniform small, round and central nuclei with evenly dispersed chromatin

Panels of markers to differentiate renal tumor subtypes:
  • 4% - 7% of adult renal epithelial tumors
  • Adults age 50+; 2/3 men; usually incidental
  • May coexist with renal cell carcinoma
  • Rarely associated with renal failure due to multiple tumors or large bilateral tumors (Arch Pathol Lab Med 2002;126:648)
  • Arises from intercalated cells of collecting duct
Clinical features
Birt-Hogg-Dubé syndrome:
  • Rare, autosomal dominant syndrome of small dome shaped papular fibrofolliculomas of face, neck and upper trunk
  • Associated with multiple renal tumors (mean 5.3), usually chromophobe carcinomas or oncocytomas, oncocytosis, pulmonary cysts and spontaneous pneumothorax (Am J Surg Pathol 2002;26:1542)
  • Associated with 17p12q11 abnormality involving folliculin protein (Arch Pathol Lab Med 2006;130:1865)
Radiology images

AFIP images

Renal oncocytoma

MR shows same tumor with prominent central scar

Case reports
Clinical images

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Giant (20 cm) tumor in pregnant woman

Gross description
  • Well circumscribed, unencapsulated, solid, homogenous, mahogany or brownish yellow (same as cortex), 3 - 6 cm, stellate central scar in larger lesions
  • 5% are bilateral or multifocal; may invade renal capsule or renal vein
  • 20% have gross hemorrhage but necrosis is rare
  • Gross appearance is an important criteria
Gross images

Contributed by Debra Zynger, M.D.

Mahogany color, central scar

Mid pole, well circumscribed

Central scar, pale brown

Serial sections

Microscopic (histologic) description
  • Nesting, alveolar or tubular patterns (closely packed at periphery, more separated centrally) of uniform round / polygonal cells with abundant, intensely eosinophilic and granular cytoplasm, uniform small, round and central nuclei with evenly dispersed chromatin and smooth contour of nuclear membrane, occasional degenerative atypia (bizarre nuclear pleomorphism), focal vacuoles possible near areas of fibrosis
  • Stroma is myxoid or hyalinized
  • Occasionally cystic change, psammoma bodies, variably sized tubular structures, capsular / perinephric fat invasion (20%), vascular invasion (5%)
  • Oncoblasts: small cells with minimal cytoplasm and dense hyperchromatic nuclei
  • No papillary pattern (although may have small papillary fronds in areas of cystic change), no clear / spindle cells, no necrosis, no perinuclear halo
  • If mitotic figures in more than one 20× field, classify as eosinophilic chromophobe carcinoma
  • Grossly noted scar is composed of central loose stroma surrounded by closely packed nests of cells
  • Nuclear grading not necessary since benign behavior (Am J Surg Pathol 1997;21:1)
Microscopic (histologic) images

AFIP images

Cytoplasm and small, round and regular nuclei

Scarred zone tumor cells

Incompletely differentiated oncocytes

Alveolar nests

Trabecular patterns

Tubulocystic pattern

Focal degenerative atypia

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Sheets of cells with abundant eosinophilic cytoplasm


Osseous metaplasia

Invasion of periphephric fat

Multicystic tumour with thickened septa

Birt-Hogg-Dubé associated tumors

Bilateral renal oncocytosis with renal failure

62 year old man -
1 & 2: nests of round to polygonal cells with abundant granular,
eosinophilic cytoplasm and central round / oval nuclei;
3: EM shows abundant abnormal mitochondria with parallel cristae


Vimentin staining


Bottom: EpCAM- (only focally
positive) versus diffusely
positive in chromophobe
renal cell carcinoma (top)

Cytology description
  • Large cells with homogenous granular cytoplasm, nuclei have no / mild nuclear membrane irregularities, tiny nucleoli, mild pleomorphism and only an occasional large, more hyperchromatic nucleus (Cancer 1999;87:161)
Cytology images

AFIP images

Abundant granular cytoplasm

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Small clusters and single cells with uniform cytoplasm


Diff-Quik shows
homogeneous granular
cytoplasm and round,
regular nuclei without grooves

Positive stains
Negative stains
Electron microscopy description
  • Marked increase in mitochondria, predominantly uniform and round with stacked parallel (lamellar) cristae, which causes the eosinophilia
  • Few microvesicles in the apical portion of the cytoplasm with rare, short and stubby microvilli
  • No / rare other organelles, lipid, glycogen, microvilli or brush border (Am J Surg Pathol 2000;24:1247)
Electron microscopy images

AFIP images

Cytoplasm is packed with large mitochondria

Molecular / cytogenetics description
Molecular / cytogenetics images

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FISH: loss of chromosomes 1 (left), 1 and 17 (right)

Differential diagnosis
  • Chromophobe carcinoma, eosinophilic variant: diffuse, solid growth but no nesting pattern; has distinct, thickened cell border; wrinkled nuclei with binucleation, perinuclear halos, mitotic figures, diffusely and strongly positive for Hale's colloidal iron, microvesicles by EM, abnromalities by interphase FISH (Am J Clin Pathol 2010;133:116)
  • Clear cell carcinoma with granular cytoplasm: compact alveolar growth pattern; also hemorrhage, necrosis and frequent mitotic figures, long microvilli by EM, 3p-
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