Diffusion-weighted magnetic resonance imaging in evaluation of primary solid and cystic renal masses using the Bosniak classification

Purpose: Our purpose was to determine whether quantitative diffusion-weighted MR imaging (DWI) could be used in discrimination of benign and malignant primary solid and cystic renal tumors.

Materials and methods: A total of 105 consecutive patients with renal masses and 30 healthy controls were enrolled in this prospective study. Dynamic contrast enhanced routin renal images and DWI (with b factors of 0, 500 and 1000 s/mm(2)) was performed at 1.5 T unit. Renal masses were divided into two groups as cystic or solid and all cystic lesions were prospectively assigned to a Bosniak classification number. The median apparent diffusion coefficient (ADC) values along with b 500 and 1000 signal intensities of normal kidneys, solid components of mixed renal masses and total of cystic lesions were calculated.

Results: The mean ADC value of normal renal parenchyma in control group was 2.18 ± 0.13 × 10(-3)mm(2)/s. Solid renal tumors had significant lower ADC values (median: 1.16 ± 0.27 × 10(-3)mm(2)/s), in contrast to cystic tumors (median: 2.73 ± 0.44 × 10(-3)mm(2)/s). The mean ADC value of the Bosniak Category I cysts was significantly higher (3.09 ± 0.14 × 10(-3)mm(2)/s) than normal renal parenchyma (p<0.01). A statistical significance was achieved between the signal intensity of Bosniak Category I and Category II-III cysts with b 1000 (p<0.05). Among the different histologic subtypes of renal cell carcinoma, the mean ADC value of chromophobe cell carcinoma (1.41 ± 0.09 × 10(-3)mm(2)/s) was significantly higher than that of papillary cell carcinoma (0.90 ± 0.16 × 10(-3)mm(2)/s) and clear cell carcinoma (1.23 ± 0.13 × 10(-3)mm(2)/s).

Conclusion: Accurate assessment of renal masses is important for establishing whether tumors require surgical intervention or not. While MRI is a useful modality as an investigative tool for diagnosing, characterizing and staging renal masses, DWI contributes additional value by promising differentiation benign from malignant renal tumors, even histologically subtyping of renal cell cancer.