A dult renal tumors have been classified into various types by the World Health Organization (1). Among them, renal oncocytoma and chromophobe renal cell carcinoma (RCC) originate from intercalated cells in the collecting duct and share some morphologic, histologic, electron microscopy findings, and immunohistochemical characteristics (2, 3). Although they have common pathologic features, renal oncocytomas are benign, whereas chromophobe RCCs are malignant. Chromophobe RCC constitutes approximately 6%-8% of all renal tumors and approximately 4%-10% of all cases of RCC (4, 5). Oncocytoma is the second most frequent benign renal parenchymal tumor, accounting for 3%-7% of all renal lesions (6).So far preoperative differentiation between oncocytomas and chromophobe RCCs could not be done accurately using imaging methods, and both tumor types have been treated surgically. Avoidance of surgery, or application of a nephron-sparing approach for benign lesions, has been an important topic for imaging studies in recent years. Some of these studies have involved computed tomography (7-13), and others magnetic resonance imaging (MRI) (12,13).In this study, we investigated the MRI features of renal tumors, namely T2 signal intensities, T2 signal intensity ratios, enhancement patterns, and enhancement ratios that might allow differentiation of oncocytoma from chromophobe RCC.
PURPOSEWe aimed to evaluate magnetic resonance imaging (MRI) features, including signal intensities, enhancement patterns and T2 signal intensity ratios to differentiate oncocytoma from chromophobe renal cell carcinoma (RCC).
METHODSThis retrospective study included 17 patients with oncocytoma and 33 patients with chromophobe RCC who underwent dynamic MRI. Two radiologists independently reviewed images blinded to pathology. Morphologic characteristics, T1 and T2 signal intensities were reviewed. T2 signal intensities, wash-in, wash-out values, T2 signal intensity ratios were calculated. Sensitivity and specificity analyses were performed.
RESULTSMean ages of patients with oncocytoma and chromophobe RCC were 61.0±11.6 and 58.5±14.0 years, respectively. Mean tumor size was 60.6±47.3 mm for oncocytoma, 61.7±45.9 mm for chromophobe RCC. Qualitative imaging findings in conventional MRI have no distinctive feature in discrimination of two tumors. Regarding signal intensity ratios, oncocytomas were higher than chromophobe RCCs. Renal oncocytomas showed higher signal intensity ratios and wash-in values than chromophobe RCCs in all phases. Fast spin-echo T2 signal intensities were higher in oncocytomas than chromophobe RCCs.
CONCLUSIONSignal intensity ratios, fast spin-echo T2 signal intensities and wash-in values constitute diagnostic parameters for discriminating between oncoytomas and chromophobes. In the excretory phase of dynamic enhanced images, oncocytomas have higher signal intensity ratio than chromophobe RCC and high wash-in values strongly imply a diagnosis of renal oncocytoma.