The value of contrast-enhanced ultrasound in the follow-up of Bosniak IIF cystic renal lesions.

Background: Contrast-enhanced ultrasound (CEUS) is increasingly used in the characterization of cystic renal lesions. Bosniak IIF lesions warrant follow-up, and their reported progression rate remains variable.

Methods: In this single-center retrospective study we assessed renal CEUS exams (SonoVue^®) with a diagnosis of Bosniak IIF lesion, conducted between 2015 and 2020. 56 patients (59 lesions) met inclusion criteria. Patient demographics, lesion morphology, follow-up adherence, and outcomes were evaluated.

Results: Significant (p = 0.037) positive correlation was found between patient age and lesion size. 33.9% of patients were immediately lost to follow-up, and they tended to be younger, albeit not significantly (p = 0.09). Recommendation for follow-up imaging was indicated in 66.1% of the initial radiological reports. Follow-up adherence was not significantly lower for lesions with absent recommendation (55% vs. 70.27%, p = 0.26). Fewer (52%) female vs. male (74.19%) patients had a follow-up recommendation (p = 0.1, not significant). 10.8% of the followed lesions demonstrated progression within 5 years. Lesion reevaluation according to the 2020 European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) criteria resulted in 77.36% agreement with 22.2% of lesions being downgraded, and a single lesion being upgraded (p = 0.0015, significant).

Conclusions: Follow-up adherence of Bosniak IIF cystic renal lesions was found to be suboptimal, with potential gender disparities. Standardization of follow-up recommendation in the report is an unmet need. Progression rate remains low, but is expected to change with the adoption of novel CEUS-specific criteria. The EFSUMB criteria in particular can improve selection of truly indeterminate lesions.

Trial registration: Retrospectively registered.