BERKELEY, CA (UroToday.com) - Renal onconcytoma is considered a benign tumor, representing around 3% to 7% of all renal tumors. Based on these considerations, the authors agree on a treatment as conservative as possible, either by nephron-sparing surgery or radiofrequency ablation, when technically feasible. Therefore, the need to be able to make a pre-operative diagnosis led to search for identifiable features of renal oncocytomas, and literature abounds on the topic. Unfortunately, to now, no imaging technique was able to accurately distinguish oncocytomas from malignant lesions. Due to this lack of specific-imaging criteria, diagnosis of oncocytoma remains based on histopathological examination of surgical or biopsy specimens.
Morphologically, a central scar is found in 54% to 80% of renal oncocytomas. However, even when present, the question of renal cell carcinoma (RCC) still arises because of the mimicking of central necrosis as classically non-enhancing areas. Whereas fibrous scars of hepatic focal nodular hyperplasia enhance on gadolinium-enhanced magnetic resonance (MR) T1-weighted sequences, such a behavior has never been described in renal oncocytomas. However, it has been described recently, in indeterminate small renal masses -- a segmental enhancement inversion during the early excretory phase of biphasic computed tomography (CT)-scan, highly characteristic of oncocytoma and related to differences in hypocellular hyalinized stroma content within the tumors. Whereas this early inversion was observed within the tumor components of masses, none of these tumors presented with a central scar, and late acquisitions were not available. Also, at this time, no imaging study of fat content of oncocytomas has been performed.
The purpose of our study was to evaluate, retrospectively, on gadopentetate (Gd)-enhanced MR images, the late enhancement of the central area of renal tumors, compatible with a central scar or with a central necrosis on T2-weighted sequences, in order to distinguish renal oncocytomas from other renal tumors. Therefore, for tumors presenting with a high signal intensity (SI) central area, a complete late enhancement was observed in our study in 74% of oncocytomas and in 12% of RCCs (p=0.05). Moreover, after calculation of fat content in tumors and spleen on in- and opposed-phase images and calculation of SI index (SII) and tumor-to-spleen ratio (TSR); SII and TSR were significantly different (p=0.02 and p=0.001 respectively) between oncocytoma and RCC groups. Combination of complete late enhancement and SII or TSR provided sensitivity of 36% and 55%, specificity of 95% and 97%, positive predictive value of 67% and 86%, and negative predictive value of 84% and 88%, respectively.
In summary, whereas, central areas of oncocytomas and of RCCs may both enhance on late Gd-enhanced MR images, a complete enhancement is highly evocative of oncocytoma. Adding a MR examination when suspecting oncocytomas may be useful and the combination with chemical shift sequence increases diagnostic performance.
F. Cornelis, MD;a A.S. Lasserre, MD;a E. Tricaud, MD;a J.C Bernhard, MD;b J. M. Ferrière, MD;bY. Le Bras, MD;a and N. Grenier, MDa as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
aDepartment of Radiology, bDepartment of Urology, Pellegrin Hospital, Place Amélie Raba Léon, 33076 Bordeaux, France