Oncocytomas are benign, nonurothelial, epithelial tumors that constitute 5% to 7% of primary renal neoplasms. Classically, an oncocytoma is a solid mass that develops in the renal parenchyma and has a central fibrous scar. Most are asymptomatic at presentation and are discovered only incidentally during evaluation of non-urological problems, but hematuria and pain occur in a minority of documented cases.
Oncocytomas can appear on CT and ultrasound as a central scar located within a homogeneous, well-circumscribed solid mass .However, this is considered nonspecific and occurs in only 33% of cases of oncocytomas. In addition, this finding does not exclude clear cell carcinoma.
“The enhancement and washout values in Hounsfield units obtained by multiphasic CT scan aid in distinguishing oncocytoma from the commonly seen subtypes of RCC in renal masses <4 cm. This preliminary study demonstrates that arterial phase enhancement greater than 500% and washout values of greater than 50% are exclusively seen in renal oncocytomas.” Differentiation of oncocytoma and renal cell carcinoma in small renal masses (<4 cm): the role of 4-phase computerized tomography Bird VG et al. World J Urol. 2010 Aug 18. [Epub ahead of print]
“In the nephrographic phase, the difference of attenuation between renal cortex and tumor lesion was highest in both entities (oncocytoma, 48.1+/-5.2HU; ccRCC, 67.5+/-12.1) but not between entities (p=0.30). In the corticomedullary phase, renal oncocytomas showed greater isodensity to the normal renal cortex (13.9+/-4.3HU) compared to clear-cell RCC (51.5+/-5.0HU; p=0.003). No further significant differences were found for the unenhanced and excretory phase.” Small Renal Oncocytomas: Differentiation with multiphase CT Gakis G et al. Eur J Radiol. 2010 Jul 26. [Epub ahead of print]
“To evaluate characteristic imaging findings of tumor attenuation in multiphase computed tomography (CT) between renal oncocytomas and clear-cell renal cell carcinoma (ccRCC) of small tumor size (</=5cm).” Small Renal Oncocytomas: Differentiation with multiphase CT Gakis G et al. Eur J Radiol. 2010 Jul 26. [Epub ahead of print]
“ 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.” Renal oncocytoma: CT features cannot reliably distinguish oncocytoma from other renal neoplasms Choudhary S et al Clin Radiol. 2009 May;64(5):517-22