Renal oncocytoma

Renal oncocytoma
Diagnosis in short
Renal oncocytoma (left of image) and normal kidney (right of image). Kidney biopsy. 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, tubulocystic carcinoma of the kidney, other renal tumours with eosinophilic cytoplasm, benign liver
Stains	Hale's colloidal iron -ve
IHC	CK7 -ve/cytoplasmic +ve, CD117 +ve, PAX8 +ve
EM	abundant mitochondria
Gross	mass, mahogany brown +/- central scar
Grossing notes	partial nephrectomy grossing, total nephrectomy for tumour grossing
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

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

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.
• May be seen in the context of renal oncocytosis.

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, rare or no binucleation.
• May have - according to Trpkov et al.:
  • Vascular invasion ~4% of cases.
  • Chromophobe-like foci (<5% of neoplasm) ~12% of cases.
  • Focal clear cell changes ~15% of cases.
  • Hemorrhage.
• ‡ Focal "degenerative" atypia can be present; it is reported in ~20% of cases.

DDx:

• Chromophobe renal cell carcinoma, eosinophilic variant.
• Succinate dehydrogenase-deficient renal cell carcinoma - emerging entity as per Vancouver classification - classically has a flocculent cytoplasm, may have oncocytoma-like areas.
• Papillary renal cell carcinoma, oncocytic variant.
• Renal hybrid oncocytic/chromophobe tumour.
• Clear cell renal cell carcinoma, eosinophilic variant.
• Tubulocystic carcinoma of the kidney.
• Other renal tumours with eosinophilic cytoplasm.
• Benign liver.

Images

Case 1

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  Oncocytoma. (WC/KGH)

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  Oncocytoma. (WC/KGH)

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  Oncocytoma. (WC/KGH)

Case 2

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  Oncocytoma - high mag. (WC/Nephron)

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  Oncocytoma - intermed. mag. (WC/Nephron)

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  Oncocytoma - low mag. (WC/Nephron)

Case 3

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  Oncocytoma - low mag. (WC/Nephron)

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  Oncocytoma - low mag. (WC/Nephron)

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  Oncocytoma - intermed. mag. (WC/Nephron)

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  Oncocytoma - high mag. (WC/Nephron)

Stains

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

IHC

• CK7 -ve/+ve (cytoplasmic).
  • Chromophobe renal cell carcinoma = cell membrane +ve.
  • Based on a mRNA study it was suggested that <50% CK7 immunostaining favours oncocytoma.
• PAX8 +ve.
• CD117 +ve.
  • ChRCC also +ve.
• GATA-3 usually -ve (38 cases negative of 47 cases).
  • +ve in low-grade oncocytic renal tumour.

Others:

• CD10 -ve/+ve.
• Amylase α-1A +ve.
• PAX2 +ve.
  • Oncocytoma 20 of 23 +ve versus ChRCC 1 of 11 +ve.
• AMACR -ve or variable.
• Vimentin -ve.

A panel:

• CK7, PAX8, CD117, CD10, Mueller-Mowry stain, GATA-3.

Comparison between some renal tumours with eosinophilic cytoplasm

Tumour	CK7	CD117	GATA3
Renal oncocytoma	-ve †	+ve	-ve/+ve
Chromophobe renal cell carcinoma	+ve ‡	+ve	-ve
Low-grade oncocytic tumour	+ve	-ve	+ve

† may have scattered positive cells
‡ diffuse and strong

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Biopsy

Kidney Mass, Left, Core Biopsy:
- Renal tumour with oncocytic cytoplasm, favour oncocytoma.

COMMENT:
The tumour is stains as follows:
POSITIVE: CD117.
NEGATIVE: Hale's colloidal iron, CK7.

Block letters

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.