Renal Cell Carcinoma: Diffusion-weighted MR Imaging for Subtype Differentiation at 3.0 T

Purpose To assess the usefulness of apparent diffusion coefficients (ADCs) for characterizing renal cell carcinoma (RCC) subtypes at 3.0 T. Materials and Methods The Institutional Review Board approved this retrospective study, and informed consent was waived. Eighty-three patients underwent diffusion-weighted (DW) magnetic resonance (MR) imaging of 85 renal masses. In each patient, precontrast single-shot spin-echo echo-planar DW imaging was performed with b values of 0 and 500 and 0 and 800 sec/mm2 by using a 3.0-T MR imaging system. Differences in ADCs between the RCC lesions and uninvolved renal parenchyma were tested by using a paired-samples t test. One-way analysis of variance was used to compare ADCs of the various RCC subtypes. Receiver operating characteristic (ROC) curve analysis was used to test the ability of ADCs in differentiating clear cell from non–clear cell RCCs. Results Pathologic diagnoses of the 85 tumors (median diameter, 4.4 cm) in the 83 patients (54 men, 29 women; age range, 23–75 years; mean age, 49.4 years) were clear cell RCC for 49 tumors, papillary RCC for 22 tumors, and chromophobic RCC for 14 tumors. With b values of 0 and 500 sec/mm2, clear cell RCCs showed a significantly higher mean ADC (1.849 × 10−3 mm2/sec) than papillary (1.087 × 10−3 mm2/sec) and chromophobic (1.307 × 10−3 mm2/sec) RCCs (P < .001); however, the difference between papillary and chromophobic RCCs was not significant (P = .068). With b values of 0 and 800 sec/mm2, clear cell RCC showed the largest mean ADC (1.698 × 10−3 mm2/sec) of the three subtypes, and the difference between each pair of subtypes was significant (P < .001). ADCs obtained with b values of 0 and 800 sec/mm2 were more effective for distinguishing clear cell from non–clear cell RCC (area under the ROC curve, 0.973): A threshold value of 1.281 × 10−3 mm2/sec permitted distinction with high sensitivity (95.9%) and specificity (94.4%). Conclusion DW imaging with b values of 0 and 800 sec/mm2 allows sensitive and specific differentiation of clear cell, papillary, and chromophobic RCCs, suggesting that DW imaging may be useful in the preoperative characterization of RCC. © RSNA, 2010