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Renal oncocytomas are classified as benign renal neoplasms in the 2004 World Health Organization classification of renal tumours.1 Cases of metastatic tumours have been documented,2–4 but subsequent reports have identified subtypes of renal tumours having similar histological morphology but having malignant potential. These tumours have been classified as either eosinophilic variants of renal cell carcinoma (RCC) or chromophobe carcinomas. Differentiating these tumours from oncocytomas has proved to be difficult and relies on a combination of histological morphology, immunohistochemistry and electron microscopy. There is still a presumption that if metastasis occurs then the tumour should not be classified as a renal oncocytoma and should be called an eosinophilic RCC.
We present a patient who presented with liver metastasis 9 years after the removal of a renal oncocytoma.
A woman in her 70s presented with left-sided abdominal pain. She was noted to have a mobile mass in the left upper quadrant. Baseline blood examinations were normal and she had no other significant medical history. An abdominal ultrasound was suggestive of a left RCC. A CT scan showed a 12 cm renal mass extending just across the midline, arising from the upper anterior part of the left kidney (fig 1). The left renal vein, liver and lymph nodes appeared unaffected. The conclusion was that this was most probably an RCC, but the pattern of enhancement was suggestive of a renal oncocytoma. A chest x ray was clear.