To assess the value of contrast-enhanced ultrasonography (CEUS) combined with the Bosniak classification in the diagnosis of renal cystic lesions.

The CEUS manifestations of 62 patients diagnosed with renal cystic lesions by conventional ultrasound and confirmed by surgical pathology at Lanzhou University Second Hospital from August 2015 to August 2020 were retrospectively analyzed and categorized by the Bosniak classification system according to the CEUS features. The value of contrast-enhanced ultrasonography combined with Bosniak classification in the diagnosis and differential diagnosis of cystic renal carcinoma was evaluated. The CEUS features of benign and malignant renal cystic lesions were compared by the Chi-square test. The sensitivity, specificity, positive predictive value, and negative predictive value of CEUS combined with Bosniak classification in the diagnosis of benign and malignant lesions were calculated. The CEUS imaging features of different subtypes of malignant cystic renal masses were analyzed and compared by the Chi-square test or Fisher's exact test.

For predicting multilocular cystic renal cell carcinomas (MCRCC), Bosniak classification ≥ Ⅲ had a sensitivity, specificity, positive predictive value, and negative predictive value of 83%, 58%, 73%, and 71%, respectively. MCRCC were more likely to have Bosniak classification Ⅲ (83%, 5/6), and CEUS often showed a multilocular cystic tumor without any enhancing solid nodule. Cystic clear cell renal cell carcinomas (CCRCC) and cystic papillary renal cell carcinomas (PRCC) were more likely to have Bosniak classification Ⅳ (86%, 6/7; 76%, 13/17). Cystic CCRCC were significantly more likely to show a multilocular pattern (65%, 11/17), and the intracystic solid components demonstrated a higher frequency of hyperenhancement (71%, 12/17). Cystic PRCC were significantly more likely to show a unilocular cystic pattern (86%, 6/7), and the intracystic solid components demonstrated a higher frequency of hypoenhancement (71%, 5/7).

CEUS combined with the Bosniak classification system is of great value in the diagnosis of benign and malignant cystic renal lesions and in the differential diagnosis of different types of cystic renal carcinoma.