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Renal Oncocytoma: Diagnosis and Therapy

Definition

Oncocytoma is a benign epithelial kidney tumor derived from intercalated cells of the collecting ducts.

Epidemiology

Oncocytomas account for 3 % to 7 % of all kidney tumors and are usually sporadic and unilateral.

Birt-Hogg-Dubé syndrome:

A rare, autosomal dominant tumor predisposition syndrome caused by germline mutations in the FLCN gene. It is associated with skin tumors, pulmonary cysts, and bilateral kidney tumors, including pure oncocytomas (5 %), hybrid oncocytic tumors (50 %), and renal cell carcinomas, particularly chromophobe renal cell carcinomas.

Pathology

Gross pathology:

A homogeneous brown kidney tumor, occasionally with a central scar.

Microscopy:

Polygonal eosinophilic cells arranged in nests. The cells are rich in mitochondria, and the nuclei are sometimes pleomorphic. Tumors with nuclear atypia or hybrid morphology can be difficult to classify as oncocytoma or renal cell carcinoma.

Diagnosis

Imaging alone cannot reliably distinguish oncocytoma from renal cell carcinoma before surgery.

Ultrasound imaging:

A solid, well-circumscribed mass [fig. ultrasound images].

CT or MRI:

A contrast-enhancing kidney tumor, often 4–6 cm in size. A central stellate scar is sometimes visible but is not a reliable diagnostic sign [fig. CT image of an oncocytoma].

Renal biopsy:

Kidney tumor biopsy may suggest oncocytoma and help avoid unnecessary surgery. Its diagnostic value is limited by sampling error and histologic overlap with chromophobe renal cell carcinoma and hybrid oncocytic-chromophobe tumors. Percutaneous kidney tumor biopsy is appropriate when the result may affect the treatment decision. Typical indications include small solid kidney tumors before active surveillance, bilateral or multiple tumors when a hereditary syndrome is suspected, and histologic confirmation before thermal ablation.

Treatment

Active surveillance:

Active surveillance is a reasonable option for a confirmed or highly likely oncocytoma, particularly for small tumors, patients at increased surgical risk, or patients who prefer surveillance. Follow-up is performed with ultrasound and MRI. Oncocytomas have a low growth rate (less than 2 mm/year).

Partial nephrectomy:

If oncocytoma is suspected before surgery, an organ-preserving approach (open, laparoscopic, or robot-assisted partial nephrectomy) should be pursued [fig. intraoperative finding].

References

Choudhary, S.; Rajesh, A.; Mayer, N. J.; Mulcahy, K. A. & Haroon, A. Renal oncocytoma: CT features cannot reliably distinguish oncocytoma from other renal neoplasms.
Clin Radiol, 2009, 64, 517-522

Liu S, Lee S, Rashid P, Bangash H, Hamid A, Lau J, Cohen R. Active surveillance is suitable for intermediate term follow-up of renal oncocytoma diagnosed by percutaneous core biopsy. BJU Int. 2016 Oct;118 Suppl 3:30-34. doi: 10.1111/bju.13538.

  Deutsche Version: Onkozytom der Nieren

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