Renal oncocytoma: CT features cannot reliably distinguish oncocytoma from other renal neoplasms

To retrospectively review the computed tomography (CT) imaging features of a series of histologically confirmed renal oncocytomas and to determine whether imaging features are predictive of this subtype of benign renal epithelial tumour.

From May 2001 to October 2007, 21 patients with 28 renal masses, confirmed as renal oncocytoma on histological examination of the resection specimen, were identified from the pathology database at our institution. The preoperative imaging findings were retrospectively analysed to determine characteristic features, if any, to predict this rare subtype of benign renal tumour.

There were 11 female and 10 male patients and the age at presentation ranged from 40-80 years (mean age 65.9 years). The size of the masses ranged from 1.2-12 cm in diameter (mean diameter 4.9 cm). All masses showed contrast enhancement. In 18 (64.3%) lesions the enhancement of the tumour was isodense to renal cortex. Ten (35.7%) lesions were hypodense to renal cortex. In three (10.7%) lesions, a well-defined stellate central scar was seen at CT and confirmed pathologically. In two (7.1%) lesions, a central scar was identified pathologically, but not seen on CT. The size of the central scars ranged from 10-29 mm diameter on CT. Twenty-two (78.6%) lesions did not demonstrate a scar on CT or pathologically. None of the patients had regional lymphadenopathy or distant metastasis.

Renal oncocytoma is typically described as being hypervascular and homogeneous, with a characteristic central stellate scar on CT. The present study demonstrates that these imaging features are found in only a small proportion of these tumours. Therefore, imaging characteristics alone are unreliable when differentiating between oncocytoma and renal cell carcinoma, and histopathological diagnosis remains the reference standard.