Case 18 - Discussion

Uploaded: 2007-01-25, Updated: 2007-11-18

CK7, 20 EMA, 40
Colloidal iron staining, 40 Colloidal iron staining,, 60
EM, 5000 EM, 5000
EM, 5000 EM, 20000
  • Diagnosis: Oncocytoma, right kidney, maximum dimension 3.5 cm;

  • IPX:  Cytokeratin 7, scattered focal strong positivity; EMA: diffuse positivity; Hale's colloidal iron - positivity at the luminal surface; RCC negative, vimentin negative;

  • Ultrastructurally, the neoplasm exclusively consists of oncocytes with uniform and round nuclei. The tumor cells have interdigitating cell membranes and abundant cytoplasm predominantly filled with mitochondria. The mitochondria are mainly round with lamellar cristae, and many of the mitochondria are arranged parallelly. Other cytoplasmic organelles are scant. The nuclear membrane is thick with one centrally localized nucleolus.

  • CYTOGENETICS REPORT: NOMENCLATURE: 46,XY[12]. Normal male chromosome complement.
    Two cells with the following non-clonal abnormalities were observed;
    47,XY,+mar = 1 cell
    46,XY,?t(10;22)(q26;q12) = 1 cell.



Related cases: renal mass 1, renal mass 2, renal mass 3, renal mass 4


The Key Features

  • Central scar, central loose hypocellular fibrous stroma;

  • Uniform granular eosinophilic cytoplasm;

  • CK7 scattered +, CD117+; Vim-, CD10-, RCC-;

  • EM: numerous mitochondria.

Clinical Futures

  • Most common benign solid renal tumor;

  • Originate from the intercalated cells of the collecting duct;

  • 3-7% of all renal tumor, 2-12% multifocal, and 4-14% bilateral;

  • M:F= 2-3:1;

  • Mean patient age is 62-68;

  • 10% of cases, oncocytoma and chromophobe RCC may coexist.

Gross Findings

  • Spherical and are large (average size, 7 cm) with a pseudocapsule or no capsule;

  • Cut sections, homogeneously tan-pale yellow, mahogany color;

  • Characteristic fleshy/stellate central scar (33-54%);

  • Necrosis, hemorrhage and calcification may be present.

Microscopic Findings

  • Large cells, granular eosinophilic cytoplasm;

  • Well-defined small nests, no sheet-like arrangement;

  • Nuclei: round/oval/smooth and round, minimal atypia, large nucleoli;

  • Some areas, the nests are separated by a loose hypocellular fibrous stroma.

Differential Diagnosis




Chromophobe RCC


Mahogany brown +/- central scar

Pale tan-brown, +/- central necrosis


Closely packed nests (periphery) and nests in loose hypocellular stroma; no trabeculae/sheets

Closely packed nests; +/-broad trabeculae/sheets


Uniform, limited atypia

Classic and eosinophic cells, more atypia


Granular, acidophilic

Granular, acidophilic with perinuclear halos


Uniform, round, degenerative pleomorphism

More pleomorphism, "raisinoid"


None or rare


Colloidal iron

Focal positivity, in the lumen.

Strongly diffuse positivity


Positive,CK7-scattered strong positive

Positive,CK7-diffusely strong positive





Numerous mitochondria with lamellar cristae;

no microvesicles

Numerous mitochondria with tubulovesicular cristae; interspersed microvesicles

Immunohistochemistry Staining

  • Cathepsin H +, EMA+, CK7-scattered strong positive, CD117+

  • RCC-, Vimentin-, CD10-

  • Colloid iron staining: focal positive

Election Microscopy

  • Abundant abnormal mitochondria


  • Losses of chromosome 1 and X chromosomes, deletion of chromosome 14 and a balanced translocation involving 11q13.

Treatment and Prognosis

  • Benign tumors, and the prognosis after total or partial nephrectomy is excellent.