Background: Renal cell carcinoma (RCC) represents the most common malignant epithelial neoplasm of the kidney. Accurate assessment of the renal masses, defining the histologic subtype and the grade of differentiation of the tumor, is vital to ensure an adequate case management as well as for staging and prognosis. Recently, diffusion-weighted imaging (DWI) magnetic resonance imaging (MRI) tends to be increasingly appealing for the clinicians as an imaging procedure of choice for the diagnosis and staging of the RCC, which is predetermined by several advantages over CT. The goal of the survey was to assess the applicability of the apparent diffusion coefficient (ADC) of the DWI MRI for the differential diagnostics, histologic subtyping, and defining the grade of differentiation of the RCC.
Methods: The study enrolled 288 adult patients with renal lesions: 188 patients with solid RCC-126 patients with clear cell subtype (ccRCC), 32 patients with papillary RCC (pRCC), 30 patients with chromophobe RCC (chRCC); 27 patient with cystic form or RCC (Bosniak cyst, category IV); 32 patients with renal angiomyolipoma (AML); 25 patients with renal oncocytoma (OC); and 16 patients with the renal abscess (AB). In total, 245 lesions were pathologically verified. As a reference, 19 healthy volunteers were included into the study. All patients underwent MRI of the kidneys, involving DWI with subsequent evaluation of the ADC.
Results: There was a reliable difference (p < 0.05) in mean ADC values between the normal renal parenchyma (NRP), solid RCC of different histologic subtypes and grades, cystic RCC, and benign renal lesions. The mean ADC values obtained in the result of the study were (×10-3 mm2/s): 2.47 ± 0.12 in NRP, 1.63 ± 0.29 in all solid RCCs, 1.82 ± 0.22 in solid ccRCC (1.92 ± 0.11-Fuhrman grade I, 1.84 ± 0.14-Fuhrman grade II, 1.79 ± 0.10-Fuhrman grade III, 1.72 ± 0.06-Fuhrman grade IV), 1.61 ± 0.07 in pRCC, 1.46 ± 0.09 in chRCC, 2.68 ± 0.11 in cystic RCC, 2.13 ± 0.08 in AML, 2.26 ± 0.06 in OC, and 3.30 ± 0.07 in AB.
Conclusion: The data received in our study demonstrate a substantial restriction of diffusion of hydrogen molecules in tissues of ccRCC in comparison with the healthy renal parenchyma preconditioned by the greater density of tumor. A statistically significant difference in mean ADC values of ccRCC with different grades of nuclear pleomorphism by Fuhrman was observed: Low-grade tumors showed higher mean ADC values compared to high-grade tumors. The modality of the MRI DWI along with ADC measurement allows to reliably differentiate between the solid RCC of main histologic subtypes and grades, cystic RCC, and the benign renal lesions.
Keywords: Apparent diffusion coefficient; Diffusion-weighted imaging; Magnetic resonance imaging; Renal cell carcinoma.