To evaluate the diagnostic value and inter-observer agreement of the 2020 adapted Bosniak cyst categorization proposed based on ultrasound for cystic renal masses (CRMs).

This retrospective study enrolled patients with surgically resected CRMs and postoperative pathology confirmation from the First Medical Center of the Chinese PLA General Hospital between October 2018 and October 2024. All patients underwent both conventional renal ultrasound and contrast enhanced ultrasound (CEUS) within one month before surgery. A total of 187 patients with 188 lesions were included in the final analysis. Four sonographers—two senior and two junior—independently reviewed the conventional ultrasound and CEUS images and classified each lesion according to the 2020 Bosniak criteria. Interobserver agreement was evaluated using Fleiss' kappa (κ) and weighted Cohen's κ, with subgroup analyses performed based on observer experience. Using pathological findings as the reference standard, receiver operating characteristic (ROC) curve analysis was conducted to assess and compare the diagnostic performance of the Bosniak classification based on conventional ultrasound versus CEUS.

Among the 188 lesions, 125 were benign and 63 were malignant. The area under the ROC curve (AUC) of conventional ultrasound and CEUS for differentiating benign and malignant CRMs was 0.872 and 0.928, respectively. The diagnostic specificity of CEUS was significantly higher than that of conventional ultrasound (90.40% vs 82.40%, P＜0.05). After excluding 88 cystic lesions (Bosniak categories Ⅰ and Ⅱ renal cysts), the diagnostic specificity of both conventional ultrasound and CEUS decreased markedly; however, CEUS still demonstrated significantly higher specificity than conventional ultrasound (67.57% vs 40.54%, P＜0.05). Interobserver agreement for CEUS classification among the four sonographers was significantly higher than that for conventional ultrasound (κ: 0.790 vs 0.565, P＜0.001). For conventional ultrasound, interobserver agreement was higher between the two senior sonographers than between the two junior sonographers (weighted κ=0.865 vs 0.746, P＜0.001). In contrast, for CEUS, there was no statistically significant difference in interobserver agreement between senior and junior sonographers (weighted κ=0.951 vs 0.921, P＞0.05). In the subgroup of CRMs including only categories Ⅱ, ⅡF, and Ⅲ, the interobserver agreement for conventional ultrasound and CEUS was κ=0.188 and κ=0.600, respectively (P＜0.001).

For the 2020 adapted Bosniak cyst categorization proposed based on ultrasound, the CEUS version demonstrates superior diagnostic performance compared to the conventional ultrasound approach, evidenced by higher interobserver agreement and improved specificity in differentiating benign from malignant CRMs.