Diffusion-weighted MRI in inflammatory renal lesions: all that glitters is not RCC!

To evaluate the diffusion characteristics of inflammatory renal lesions and assess whether apparent diffusion coefficient (ADC) values can distinguish them from renal-cell carcinomas (RCCs). Eighty-eight patients underwent multidetector computed tomography (MDCT), magnetic resonance imaging (MRI) and diffusion-weighted (DW) MRI (at b values of 0 and 500 s/mm(2)) for characterisation of focal renal lesions. On retrospective evaluation, 15 patients had 20 inflammatory lesions and 33 patients had 36 RCCs. DW images were compared and receiver operating characteristic (ROC) curves were drawn to establish cut-off ADC values. All inflammatory lesions and 91.7% of RCCs showed restricted diffusion. DW images showed markedly restricted diffusion in fluid intensity areas of abscesses, whereas RCCs showed free diffusion in their cystic portions. Quantitatively, both abscesses and RCCs showed ADC values significantly lower than normal renal parenchyma [1.12 and 1.56 respectively vs 2.34 (x 10(-3) mm(2)/s) for normal kidney] (P < 0.0001 for both) and significantly different from each other (P < 0.0001). ROC analysis in differentiating inflammatory lesions and RCC revealed high sensitivity (100%) and specificity (78.1%) for cut-off ADC value of 1.41 (x 10(-3) mm(2)/s). Both abscess and RCC showed restricted diffusion, the former did so to a greater extent, distinctly in fluid components. Thus, ADC values provide an additional paradigm for characterisation of indeterminate renal lesions.