Objectives: To compare the diagnostic performance of computed tomography, magnetic resonance imaging and contrast enhanced ultrasonography for the assessment of complex renal cysts. Methods: We carried out a prospective single-center study from January 2012 to December 2013. We included patients with Bosniak category 2F or 3 renal cysts found on computed tomography and reviewed by two expert radiologists. Magnetic resonance imaging and contrast-enhanced ultrasonography were then carried out. Patients with a Bosniak ≥3 cyst on magnetic resonance imaging, as well as those upgraded as appearing malignant on contrast-enhanced ultrasonography, were surgically managed. Imaging results were compared with histological data. For patients without surgery, imaging examinations were compared with follow-up data. For each imaging examination, diagnostic performance and Cohen's kappa coefficient were assessed. Results: A total of 47 patients were included. The median follow up was 36 months (range 17-48 months). At initial computed tomography, cysts were classified as Bosniak 2F and Bosniak ≥3 in 34 and 13 patients, respectively. Magnetic resonance imaging found 13 Bosniak ≥3 cysts, and contrast-enhanced ultrasonography upgraded six more patients with cysts that appeared malignant. A total of 19 patients had surgery. Histological analysis reported 14 malignant tumors. No tumor progression was found in followed-up patients. Computed tomography showed poor sensitivity (36%) and specificity (76%; j = 0.11). Magnetic resonance imaging showed 71% sensitivity and 91% specificity (j = 0.64). Contrast-enhanced ultrasonography showed high sensitivity (100%) and specificity (97%), and a negative predictive value at 100% (j = 0.95). Conclusions: The present results suggested that contrast-enhanced ultrasonography could be useful in improving the assessment of complex renal cysts. Indeed, computed tomography accuracy might be limited in this indication requiring further investigations to determine the best treatment strategy.

These results confirmed that cystic renal malignancies have excellent prognosis. Bosniak III cysts had a low malignant potential, which suggests surveillance could be an option for these lesions.

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