Imaging Assessment of Complex Renal Cysts: Comparative Value of Superb Microvascular Imaging and Contrast-Enhanced Ultrasound

Background: Accurate characterization of complex renal cystic lesions is essential for individualized patient management, as enhancement patterns of septa and walls determine Bosniak classification, malignancy risk, and tailored follow-up strategies. While contrast-enhanced ultrasound (CEUS) is widely used to assess enhancement, Superb Microvascular Imaging (SMI) offers a non-contrast alternative that is capable of detecting slow-flow microvascular signals. This study aimed to evaluate the diagnostic concordance, accuracy, and reproducibility of SMI compared with CEUS in the Bosniak 2019 classification, and to explore its role in personalized imaging pathways for patients with contraindications to contrast media. Methods: Eighty patients (92 cystic renal lesions) who underwent both SMI and CEUS between January 2024 and July 2025 were retrospectively analyzed. Lesions were categorized using the Bosniak 2019 criteria. CEUS served as the reference standard. Concordance between modalities was evaluated using Cohen’s κ, and diagnostic accuracy was determined by ROC analysis. Inter- and intra-reader agreement were assessed with κ and intraclass correlation coefficients (ICC), respectively. Histopathologic confirmation was available for resected Bosniak III–IV lesions. Results: SMI showed excellent concordance with CEUS (κ = 0.84, 95% CI 0.76–0.91; overall agreement 83.7%). Concordance was perfect for Bosniak I–II, good for IIF (85%), and moderate for III (68%) and IV (64%) categories. Using CEUS as the reference, SMI achieved a sensitivity of 88.5%, specificity of 90.0%, and AUC of 0.94 for distinguishing low- from high-risk lesions. Inter-reader (κ = 0.83) and intra-reader (ICC = 0.91) agreements were excellent. Among 18 surgically resected Bosniak III–IV lesions, 14 (77.8%) were malignant; SMI correctly identified 12/14 malignant and 3/4 benign cases. Conclusions: SMI shows high diagnostic accuracy and reproducibility in the assessment of complex renal cystic lesions, with strong concordance to CEUS within the Bosniak 2019 system. By providing vascular characterization without contrast administration, SMI supports more personalized renal cyst management, enabling safer imaging for patients at risk from contrast agents and potentially reducing unnecessary interventions. Further multicenter validation is warranted to define its integration into precision-oriented multiparametric renal ultrasound protocols.