The Predictive Power of Bosniak 3 and 4 Cystic Renal Lesion Categorization Using Contrast-Enhanced Ultrasound

OBJECTIVES

Contrast-enhanced ultrasound (CEUS) is increasingly utilized for the noninvasive assessment of renal cystic lesions, using the Bosniak grading system. Bosniak 3-4 lesions require surgical referral, which allows correlation with the histopathological outcome.

METHODS

In this single-center, retrospective study we evaluated renal CEUS exams conducted with SonoVue® with a diagnosis of a Bosniak 3 or 4 lesion between 2019 and 2022. A total of 49 patients and 50 lesions met the inclusion criteria, 31 lesions had available histopathological results. Patient demographics, cyst morphology, and dominant imaging features were registered. The histopathological diagnosis was considered a reference standard.

RESULTS

Positive predictive power (PPV) for neoplastic lesions was comparable in the Bosniak 3 and 4 categories (75 vs 93.3%, P = .33), while PPV for histopathologically malignant lesion was considerably higher in the latter group (25 vs 93.33%, P = .0002). None of the lesions which had vividly enhancing thin septa as their dominant CEUS feature were malignant. Oncocytoma, multilocular cystic renal neoplasm of low malignant potential, and cystic nephroma were the major benign entities among Bosniak 3 lesions. Localized cystic kidney disease and hemorrhagic cysts were found to be the primary mimickers leading to false positive imaging findings.

CONCLUSIONS

CEUS has a high predictive power for malignancy in the Bosniak 4 category, which is not maintained in the Bosniak 3 group due to the large proportion of benign lesions. Adherence to rigorous rule-in criteria and active surveillance strategies need to be considered for equivocal CEUS Bosniak 3 lesions.

Additional value of microvascular flow imaging in the assessment of cystic and solid renal lesions

Background

Contrast enhanced ultrasound (CEUS) is increasingly used in the evaluation of renal lesions, however, its availability remains limited. Thus, sensitive noncontrast ultrasound evaluation of renal lesion vascularity is an unmet need.

Methods

In this single-center, retrospective study we assessed microvascular flow imaging (MV-flow) compared to CEUS in the evaluation of complex renal cysts and solid lesions. Out of 92 patients 28 were evaluated with both CEUS and MV-flow. Color Doppler, CEUS, and MV-flow was performed in 13 cases, whilst MV-flow, CEUS, and contrast-enhanced MV-flow (CE-MV-flow) was done in 16 cases. The CEUS diagnosis was considered gold standard.

Results

MV-flow showed a substantial agreement with the CEUS diagnosis (weighted Kappa = 0.806), excluding equivocal lesions (Bosniak 2F). MV-flow substantially outperformed color Doppler (weighted Kappa = 0.77 vs. 0.133). The agreement of CE-MV-flow and MV-flow was comparable (weighted Kappa = 0.79 vs. 0.69).

Conclusion

MV-flow significantly improves evaluation of renal lesion vascularity compared to conventional techniques. However, the sensitivity is limited for equivocal lesions (e.g. Bosniak 2F cysts). Thus, MV-flow should be used as an ancillary technique, not as a substitute to CEUS. Current MV-flow presets are ill-suited for postcontrast imaging, therefore specific presets optimized for this purpose are needed to establish its potential.