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Case 18 - Discussion

Surgical Pathology Case

 

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

  • IHC and special staining:  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.

Oncocytoma

 

The Key Features

  • Central scar with loose hypocellular fibrous stroma

  • Uniform granular eosinophilic cytoplasm

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

  • Colloid iron luminal surface positive

  • 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

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

Gross Findings

 
  • Spherical and large. average 7 cm, with a pseudocapsule or no capsule

  • Cut sections, homogeneously tan-pale yellow, mahogany

  • Characteristic fleshy/stellate central scar in 33-54% of cases

  • Necrosis, hemorrhage and calcification may be present.

Microscopic Findings

 
  • Large monotonous cells, arranged in well-defined small nests, glandular or tubular structures

  • Do not form papillary, sheet or solid nest structure

  • Nuclei: smooth and round, minimal atypia, large nucleoli

  • Granular eosinophilic cytoplasm

  • In some areas, the tumor nests are separated by a loose hypocellular fibrous stroma

Differential Diagnosis

 

 

Oncocytoma

Chromophobe RCC

Gross

Mahogany brown +/- central scar

Pale tan-brown, +/- central necrosis

Architecture

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

Closely packed solid nests;

+/-broad trabeculae/sheets

Cell

Uniform, limited atypia

Classic and eosinophilic cells, more atypia

Cytoplasm

Granular, acidophilic

Granular, acidophilic with perinuclear halos

Nuclei

Uniform, round, degenerative pleomorphism

More pleomorphism, "raisinoid"

Mitoses

None or rare

Occasional

Colloidal iron

Focal  positivity on lumen surface

Strong and diffuse cytoplasmic positivity

CK7

Most cells negative, scattered cells strongly positive

Diffusely, strongly positive

Vimentin

Negative

Negative

Ultrastructure

Numerous mitochondria with lamellar cristae;

no microvesicles

Numerous mitochondria with tubulovesicular cristae; interspersed microvesicles

Cytogenetics Occasional loss of chromosomes 1 and X Multiple monosomies

Immunohistochemistry Staining

 
  • Cathepsin H +, EMA+,  CD117+

  • CK7: most tumor cells negative, only scattered cells strongly positive

  • RCC-, Vimentin-, CD10-

  • Colloid iron staining: focally positive on the lumen surface

Election Microscopy

 
  • Abundant abnormal mitochondria

Cytogenetics

 
  • 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.

Reference

 
  • http://emedicine.com/radio/topic484.htm

  • AFIP, 4th series

  • Essential of Anatomic Pathology. Liang Cheng. 2nd Edition.