Application of Contrast-enhanced Ultrasound and Bosniak Classification to the Diagnosis of Cystic Renal Masses

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.

Long-Term Follow-Up of Non-Enhancing Renal Masses on CEUS

PURPOSE

To determine the natural history and necessity of long-term follow-up of renal masses that do not demonstrate enhancement on contrast-enhanced ultrasound (CEUS).

METHODS

This retrospective single-center study was approved by our local IRB and is HIPAA compliant. Exactly 405 patients with 620 non-enhancing renal masses on CEUS from a previously reported study were followed for up to 10 years. Techniques and equipment are described in the original manuscript. Patient charts and imaging studies were reviewed for the change in features. There were 117 (18.6%) patients lost to follow-up leading to 341 patients with 512 lesions. The lesion size, patient age, number of lesions per patient, and Bosniak class assigned at the initial examination was recorded.

RESULTS

Mean patient age was 66 ± 12.6 years (range 17-95 years). Average time of follow-up was 58.9 ± 41.7 months (range 1-207 months). There was a mean of 1.5 ± 1.0 lesions per patient (range 1-7 lesions). Lesion size was 24.9 ± 18.2 mm (range 3-161 mm). There were 276 (53.9%) patients with >5-year follow-up and 78 (15.2%) patients with >10-year follow-up. The probability of change within 5 years was 0% (95% CI: 0-0.37 per 100PY) and 10 years 0% (95% CI: 0.0-0.18 per 100PY). Two lesions (0.4%) resolved by 60 months. Five lesions (1.0%) decreased in size. Four lesions (0.8%) increased in size >20% during the follow-up period but remained benign on subsequent imaging.

CONCLUSION

Any non-enhancing renal mass on CEUS can be classified as benign.