The Bosniak classification of renal cysts have been a cornerstone in the management of cystic renal lesions by stratifying malignancy risk. Traditionally, the Bosniak classification has been based on computed tomography studies. Contrast-enhanced ultrasound (CEUS) has emerged as a radiation-free alternative, offering real-time assessment with improved sensitivity for internal septations and vascular flow. However, its efficacy in applying Bosniak criteria for cystic renal lesion classification remains under-explored. This retrospective study assesses the accuracy and clinical utility of CEUS in applying the Bosniak classification system for cystic renal lesions, comparing its performance to CT-based diagnoses.

We reviewed imaging and clinical outcomes of 85 patients with cystic renal lesions who underwent both CT and CEUS between 2017 and 2023. Lesions were classified into Bosniak categories I-IV based on CEUS findings, and results were compared to CT classifications. Histopathology, when available, and follow-up imaging were used to confirm malignancy or benign status.

CEUS provided accurate Bosniak classification in 78% of cases compared to CT. In Bosniak III and IV lesions, CEUS demonstrated a high specificity (92%) and sensitivity (85%) for identifying malignancy, especially in detecting septal vascularity and soft-tissue nodularity. CEUS reclassified 10% of lesions initially categorised as Bosniak II by CT to higher-risk categories, which was corroborated by pathology in most cases.

CEUS demonstrates reliable accuracy in Bosniak classification of cystic renal lesions, with particular strength in detecting higher-risk features. These findings support CEUS as a valuable adjunct in the evaluation of cystic renal lesions, potentially allowing for safer and more accurate patient management. Prospective studies are warranted to further validate these findings.