Functional MRI in characterization of cystic renal masses

Abstract Background Contrast-enhanced MRI using the Bosniak classification is the standard imaging approach for evaluating cystic renal masses. Diffusion-weighted imaging (DWI), a functional MRI technique that does not require contrast administration, is not included in the updated Bosniak classification (2019), despite its potential value, particularly in patients with contraindications to contrast media. Objective To evaluate the diagnostic accuracy of diffusion-weighted MRI parameters, including apparent diffusion coefficient (ADC) values and septal thickness, in differentiating benign from malignant cystic renal lesions, and to compare their performance with contrast-enhanced MRI–based findings. Results On contrast-enhanced MRI, wall enhancement did not differ significantly between malignant and benign lesions, whereas septal enhancement showed a statistically significant difference. Mean ADC values were significantly lower in malignant compared with benign cystic renal lesions. ROC curve analysis identified an optimal ADC cut-off value of ≤ 0.985 × 10 −3 mm 2 /s for differentiating malignant from benign lesions. Conclusion Diffusion-weighted MRI provides valuable quantitative information in the assessment of complex cystic renal masses. While contrast-enhanced MRI remains the reference imaging approach, DWI—particularly ADC value assessment—demonstrates high sensitivity and may serve as a complementary tool, especially in patients with contraindications to contrast administration.