Imaging Pearls ❯ Kidney ❯ Oncocytoma
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- 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