Renal oncocytoma

Renal oncocytoma is a benign kidney tumour that is removed to exclude malignancy.

Renal oncocytoma
Diagnosis in short
Renal oncocytoma. H&E stain.
LM	abundant eosinophilic cytoplasm - slightly granular, cells arranged in nests, nuclei uniform and round without significant pleomorphism
LM DDx	chromophobe renal cell carcinoma eosinophilic variant, clear cell renal cell carcinoma eosinophilic variant, papillary renal cell carcinoma oncocytic variant
Stains	Hale's colloidal iron -ve
IHC	CK7 -ve/cytoplasmic +ve, PAX2 +ve
EM	abundant mitochondria
Gross	mass, mahogany brown +/- central scar
Site	kidney - see kidney tumours
Clinical history	often incidentally discovered mass
Radiology	renal mass with central scar (classic)
Prognosis	benign
Clin. DDx	other kidney tumours

General

• Can be difficult to distinguish radiologically from RCC (chromophobe subtype).
  • ... and pathologists occasionally struggle like the radiologists.
• Benign tumour - the reason it is excised is... one cannot be certain it isn't a RCC.

Gross

• Mass, mahogany brown.
  • Well circumscribed.
  • 1/3 have a characteristic central scar.

Image

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  Renal oncocytoma with central scar. (WP)

Microscopic

Features:

• Eosinophilic cytoplasm - slightly granular key feature.
• Cells arranged in nests.
• Nuclei uniform and round.
  • Slightly enlarged nuclei, but no significant pleomorphism (size variation) - important.

Notes:

• May look like eosinophilic variant of chromophobe RCC -- this is the main DDx.
  • A comparison based on histomorphology: Tabular comparison between ChRCC & oncocytoma.
    • Oncocytoma typically has: no perinuclear clearing, no raisinoid nuclei, no binucleation.

DDx:

• Chromophobe renal cell carcinoma, eosinophilic variant.
• Clear cell renal cell carcinoma, eosinophilic variant.

Images

• 

  Oncocytoma - high mag. (WC/Nephron)

• 

  Oncocytoma - intermed. mag. (WC/Nephron)

• 

  Oncocytoma - low mag. (WC/Nephron)

Stains

• Hale's colloidal iron -ve.
  • ChRCC +ve (blue granular cytoplasmic).

IHC

• CK7 -ve/+ve (cytoplasmic) .
  • Chromophobe renal cell carcinoma = cell membrane +ve.

• PAX2 +ve.
  • Oncocytoma 20 of 23 +ve versus ChRCC 1 of 11 +ve.

• Amylase α-1A +ve.

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Biopsy

KIDNEY MASS, RIGHT, CORE BIOPSY:
- RENAL TUMOUR WITH ONCOCYTIC CYTOPLASM, FAVOUR ONCOCYTOMA.

COMMENT:
The tumour is CK7 negative and Hale's colloidal iron negative.

Micro

The sections show a tumour with cells arranged in nests. The tumour cells have abundant eosinophilic cytoplasm. The tumour cell nuclei are predominantly round. No perinuclear halos are apparent. Binucleation is not common. No zonal necrosis is identified. Focally, tumour nests are spaced reminiscent of an archipelago. Mitoses are not apparent. The tumour is moderately circumscribed.

A small amount of renal parenchyma is present. No definite glomeruli are identified. No significant interstitial fibrosis is present. No inflammation is apparent.

Resection

PORTION OF KIDNEY, LEFT, PARTIAL NEPHRECTOMY:
- ONCOCYTOMA.

COMMENT:
The tumour is CK7 negative and Hale's colloidal iron negative.

Micro

The sections show a tumour with cells arranged in nests. The tumour cells have abundant eosinophilic cytoplasm. The tumour cell nuclei are round and have round nucleoli. No perinuclear halos are apparent. Binucleation is not common. No zonal necrosis is identified. Focally, tumour nests are spaced reminiscent of an archipelago. Mitoses are not apparent. The tumour is moderately circumscribed and is completely excised in the planes of section.

The thin rim of renal parenchyma has no apparent glomerular pathology on the H&E stained sections. Mild-to-moderate atherosclerosis is present. Mild arteriolar hyalinization is identified.

The Hale's colloidal iron stain is negative in the tumour. A CK7 immunostain has very rare positive cells within the tumour; this is interpreted overall as negative.

See also

• Kidney tumours.
• Oncocytoma.