Differential diagnosis of the small renal masses: role of the apparent diffusion coefficient of the diffusion-weighted MRI

Renal cell carcinoma (RCC) accounts for approximately 3% of adult malignancies and more than 90% of neoplasms arising from the kidney. Uninformative percutaneous kidney biopsies vary from 10 to 23%. As a result, 7.5-33.6% of partial nephrectomies in patients with small renal masses (SRM) are performed on benign renal tumors. The aim of this study was to assess the feasibility of the apparent diffusion coefficient (ADC) of the diffusion-weighted imaging (DWI) of MRI, as RCC imaging biomarker for differentiation of SRM.

Adult patients (n = 158) with 170 SRM were enrolled into this study. The control group were healthy volunteers with normal clinical and radiologic findings (n = 15). All participants underwent MRI with DWI sequence included.

Mean ADC values of solid RCC (1.65 ± 0.38 × 10-3 mm2/s) were lower than healthy renal parenchyma (2.47 ± 0.12 × 10-3 mm2/s, p < 0.05). There was no difference between mean ADC values of ccRCC, pRCC and chRCC (1.82 ± 0.22 × 10-3 vs 1.61 ± 0.07 × 10-3 vs 1.46 ± 0.09 × 10-3 mm2/s, respectively, p = ns). An inverse relationship between mean ADC values and Fuhrman grade of nuclear atypia of solid ccRCCs was observed: grade I-1.92 ± 0.11 × 10-3 mm2/s, grade II-1.84 ± 0.14 × 10-3 mm2/s, grade III-1.79 ± 0.10 × 10-3 mm2/s, grade IV-1.72 ± 0.06 × 10-3 mm2/s. This was significant (p < 0.05) only between tumors of I and IV grades. Significant difference (p < 0.05) between mean ADC values of solid RCCs, benign renal tumors and renal cysts was observed (1.65 ± 0.38 × 10-3 vs 2.23 ± 0.18 × 10-3 vs 3.15 ± 0.51 × 10-3 mm2/s, respectively). In addition, there was a significant difference (p < 0.05) in mean ADC values between benign cysts and cystic RCC (3.36 ± 0.35 × 10-3 vs 2.83 ± 0.21 × 10-3 mm2/s, respectively).

ADC maps with b values of 0 and 800 s/mm2 can be used as an imaging biomarker, to differentiate benign SRM from malignant SRM. Using ADC value threshold of 1.75 × 10-3 mm2/s allows to differentiate solid RCC from solid benign kidney tumors with 91% sensitivity and 89% specificity; ADC value threshold of 2.96 × 10-3 mm2/s distinguishes cystic RCC from benign renal cysts with 90% sensitivity and 88% specificity. However, the possibility of differentiation between ccRCC histologic subtypes and grades, utilizing ADC values, is limited.

International urology and nephrology. 2017 Dec 11 [Epub ahead of print]

Yulian Mytsyk, Ihor Dutka, Borys Yuriy, Iryna Maksymovych, Martin Caprnda, Katarina Gazdikova, Luis Rodrigo, Peter Kruzliak, Polina Illjuk, Ammad Ahmad Farooqi

Department of Urology, Lviv National Medical University, Pekarska Str. 69, Lviv, Ukraine. ., Euroclinic Medical Center, Lviv, Ukraine., Department of Urology, Lviv National Medical University, Pekarska Str. 69, Lviv, Ukraine., Department of Radiology, Lviv National Medical University, Lviv, Ukraine., 1st Department of Internal Medicine, Faculty of Medicine, Comenius University and University Hospital, Bratislava, Slovak Republic., Department of Nutrition, Faculty of Nursing and Professional Health Studies, Slovak Medical University, Limbova 12, 833 03, Bratislava, Slovak Republic. ., Faculty of Medicine, Central University Hospital of Asturias (HUCA), University of Oviedo, Oviedo, Spain., 2nd Department of Surgery, Faculty of Medicine, St. Anne's University Hospital, Masaryk University, Brno, Czech Republic. ., Laboratory for Translational Oncology and Personalized Medicine, Rashid Latif Medical College, Lahore, Pakistan.