Diffusion-weighted MRI in renal cell carcinoma: A surrogate marker for predicting nuclear grade and histological subtype

Background: Though previous investigators have attempted to evaluate its utility in characterization of focal renal lesions, diffusion-weighted MR imaging (DW MRI) in renal diseases is still an evolving field and its role in predicting the aggressiveness of renal cell carcinoma (RCC) is yet to be established. Purpose: To assess whether apparent diffusion coefficient (ADC) values can be used to determine the nuclear grade and histological subtype of RCCs and to identify the tumor attributes contributing to variation in ADC values. Material and Methods: The institutional ethics committee waived the requirement of informed consent for this retrospective study. The study cohort consisted of 33 patients who underwent MRI (with diffusion-weighted imaging at b values of 0 and 500 s/mm(2)) and were found to have 36 pathologically-proven RCCs. ADC values were determined for solid portions of RCC, cystic/hemorrhagic areas, and normal renal parenchyma. Histological subtype, nuclear grade, and cell count were determined for each lesion. ADC values were compared between different grades and subtypes and correlation with cell count was investigated. Receiver operating characteristic curves were drawn to establish cut-off ADC values. Results: There were 23 low grade (grades I and II) and 13 high grade tumors (grades ill and IV). There were 32 clear-cell and four non-clear-cell RCCs. A decreasing trend of ADC values was seen with increasing grade and mean ADC of high grade RCC was significantly lower than low grade (1.3145 vs 1.6982 x 10(-3) mm(2)/s) (P = 0.005). Mean ADC for clear-cell RCC was significantly higher than non-clear-cell RCC (1.6245 vs. 1.0412 x 10(-3) mm(2)/s) (P = 0.005). ADC values higher than 1.7960 x 10(-3) mm(2)/s were seen only with low grade and values greater than 1.4904 x 10(-3) mm(2)/s were seen only with clear-cell RCC. Conclusion: ADC values provide a non-invasive means to predict the nuclear grade and histological subtype of RCC. Cellularity and morphology are other tumor attributes contributing to the variation in ADC values of RCCs.