Objective: Focal renal lesions are common incidental findings on computed tomography (CT). For lesions with a cystic appearance, the Bosniak classification system has enabled an important separation of benign and (potentially) malignant cysts, giving a practical guide for management. The purpose of this study was to evaluate contrast-enhanced ultrasound (CEUS) as a problem-solving modality for classification of indeterminate renal lesions detected with CT.
Materials and methods: In total, 140 consecutive patients with 148 indeterminate renal lesions were examined with ultrasound combined with CEUS (81 men and 59 women with mean age 63.8 years).
Results: Altogether, 146 lesions were classified by CEUS in categories according to the Bosniak classification system, or as solid lesions. Mean lesion diameter was 30 mm (range 5-166 mm). Nine lesions were classified as category I, 32 as category II and 59 as category IIF ("non-surgical lesions"). 48 IIF cysts were followed for a minimum of 2 years (mean 4 years and 8 months): three lesions were upgraded to category III (6%) and 45 were stable category. 19 lesions had a more complex cystic appearance: 12 were classified as category III and seven as category IV cysts. 27 lesions were diagnosed as solid, enhancing tumors. In total, 25 patients with lesions of category III, IV and solid ("surgical lesions") underwent renal surgery, with malignancy diagnosed in 18.
Conclusion: In the common setting of indeterminate renal lesions incidentally detected with a CT exam, CEUS has the potential to classify lesions into "non-surgical" and "surgical" categories, providing a platform for urological decision making, while avoiding radiation exposure.
Keywords: Bosniak classification; complex renal cysts; contrast-enhanced ultrasound; kidney.