BACKGROUNDRenal clear cell carcinoma (RCCC) is the most common malignant renal tumor. It is highly malignant, does not cause clinical symptoms in its early stages, and cannot be diagnosed using conventional ultrasound. This study was aimed to investigate the contrast-enhanced ultrasound (CEUS) mode and characteristics of the time-intensity curve for RCCC and its pathological basis.

METHODSForty-two patients with pathologically diagnosed RCCC underwent CEUS examination before surgery. The patients' kidneys were visualized after injection of contrast agents using the Technos MPX DU8. We analyzed the CEUS mode, time-intensity curve, and pathological findings.

RESULTSThe detection rate of RCCC with conventional ultrasound was about 71%, while the rate using CEUS was 100%. Larger tumors (33 cases) showed non-uniform enhancement with defective filling. CEUS modes were divided into 4 types: type I, "quick in and out" (26.19%, 11/42); type II, "quick in and slow out" (40.48%, 17/42); type III, "Simultaneous in and out" (16.67%, 7/42); and type IV "slow in and out" (16.67%, 7/42). All types had a close correlation to the pathological basis. Time-intensity curve of CEUS consisted of 3 phases, the perfusion phase, regression phase, and lag phase. Cases of types I and III only had a perfusion and regression phase, those of type II and IV had a perfusion phase, regression phase, and lag phase. Quantitative analysis of the time-intensity curve showed that the time-to-peak (TTP) of the lesions was shorter than that of normal renal parenchyma (P < 0.0001), the mean value of the up slope rate of the absolute value of lesions was higher than that of the ipsilateral normal renal parenchyma (P < 0.0001), and that the mean value of descent slope rate of the absolute value of lesions was lower than that of the ipsilateral normal renal parenchyma (P < 0.0001).

CONCLUSIONSCEUS is useful in detecting small vessels in tumors. Although there are several different CEUS modes, type I "quick in and out" and type II "quick in and slow out" accounted for the most cases that had a close correlation to pathologic angiogenesis. Time-intensity curves also showed some special characteristics. These data could provide valuable information for the clinical diagnosis of RCCC.