[The diagnostic value of multimodal blood flow imaging for benign and malignant small renal tumors]

Objective: To investigate the diagnostic value of multimodal blood flow imaging in differentiating benign and malignant small renal masses (SRMs). Methods: A total of 170 patients with renal tumors (172 lesions) who underwent surgical treatment at Tianjin Medical University Cancer Institute and Hospital from January 2020 to December 2023 were enrolled.The maximum diameter of the tumors was ≤4 cm. All patients received Color Doppler flow imaging (CDFI), Power Doppler imaging (PDI), Microflow imaging (MFI), and Contrast-enhanced ultrasound (CEUS) examinations before surgery. Two sonologists were responsible for grading the blood flow and evaluating the vascular morphology to make a diagnosis of whether the tumors were benign or malignant. Taking the postoperative pathological diagnosis as the gold standard, the receiver operating characteristic (ROC) curve analysis was used to compare the diagnostic efficacy of the four ultrasound examination methods. Results: Among the 172 lesions, 141 were malignant and 31 were benign. In the MFI imaging mode, the Kappa value for the evaluation of SRMs blood flow grading by two independent sonologists was 0.819, and the Kappa value for vascular morphology was 0.806.The detection rate of MFI for lesions with blood flow grading of 2-3 and vascular morphology of types Ⅳ-Ⅴ was 77.9% (134/172), which was higher than that of CDFI [36.6% (63/172)] and PDI [43.0% (74/172)]. Blood flow grading of 2-3 and vascular morphology of types Ⅳ-Ⅴ in the MFI mode could serve as independent predictors for malignant SRMs (P＜0.001). In the CEUS mode, malignant SRMs mainly manifested as fast wash-in (75.9%), fast wash-out (70.9%), and high enhancement (85.1%). In contrast, benign SRMs mainly showed slow wash-in (51.6%), slow wash-out (45.2%), and low enhancement (45.2%). Ring enhancement was observed in 37.6% of malignant SRMs, while no ring enhancement was detected in any of the benign SRMs. All these differences were statistically significant (P＜0.001).The accuracy of CDFI, PDI, MFI, and CEUS in diagnosing malignant SRMs was 0.500, 0.552, 0.855, and 0.901, respectively; the sensitivity was 0.418, 0.489, 0.887, and 0.986, respectively; the specificity was 0.871, 0.839, 0.710, and 0.516, respectively; and the area under the curve (AUC) was 0.645, 0.664, 0.798, and 0.751, respectively. Overall, MFI and CEUS demonstrated more superior diagnostic efficacy for SRMs. Conclusions: MFI exhibits high sensitivity in detecting the microvascular flow signals of SRMs. It shows comparable diagnostic performance to CEUS in differentiating the benign and malignant SRMs. It is a non-invasive, safe, cost-effective, and highly repeatable examination method.