Experimental Studies Of Contrast-enhanced Ultrasonography For Sentinel Lymph Node Detection In Breast Cancer

Purpose:1. To investigate ultrasound contrast imaging characteristics of SentinelLymph Node (SLN) in breast cancer by observing both lymphatic and SLNperfusion in rabbit VX2 breast cancer model using contrast pulse sequence(CPS) imaging via subcutaneous injection of ultrasound contrast agentSonoVue.2. To explore whether percutaneous contrast-enhanced ultrasonography(CEUS) can accurately detect SLN and reflect the situation of lymph nodemetastasis of breast cancer by comparing the detection rate of SLN viagray-scale ultrasound, CEUS and methylene blue staining.Methods:Fifteen VX2 breast cancer lymph node metastasis models in rabbit weresuccessfully established by injection of tumor tissue mass suspension.Adopt acuson sequoia 512 color Doppler ultrasonoscope matched withcontrast pulse sequences contrast imaging and 15L8-S linear array probe(frequency, 7-14 MHz) were used. Flow spectrum and artery spectrum imagesof axillary lymph nodes were observed using the ordinary two-dimensionalmodel, and the distribution of blood flow signals were also observed by usingcolor and power Doppler, and arterial spectrum and determination of theresistance index were obtained by using pulsed Doppler.Characteristics of lymph node metastasis were as follows: lymph nodesaccompanied with rounded shape (aspect ratio﹤2), irregular margins, lack of hilar or displacement, cortical thickening, heterogeneous echotexture,calcification, necrosis, peripheral or mixed vascular pattern and resistanceindex (RI)﹥0.6. And metastatic SLN was judged to have at least two of theabove signs.Nodes perfusion imaging were collected by using contrast pulsesequence imaging (mechanical index, 0.20). 0.25ml SonoVue wasadministered subcutaneously at four points (in the direction of clock 3, 6, 9,and 12) around the tumors of 15 new zealand rabbits bearing VX2 breastcancer. And the scanning process was recorded at the same time. The nodeswith enhancement of typeⅡ,ⅢandⅣwere classified as malignant whilethose with enhancement of typeⅠwas classified as benign.After nodes perfusion imaging, 0.1ml methylene blue tracer wassubcutaneously injected around the tumor according to the methods asdescribed above. The lymphatic drainage area was surgical isolated andexposed. The blue-stained lymph nodes were traced along the blue-stainedlymphatic before axillary lymph nodes were resected for pathologicalexamination.The nodes, which were stained by methylene blue, were malignant SLN,whereas the unstained were defined as benign SLN.According to the gold standard of the results of pathological examination,the resected lymph nodes were used for pathological examination to evaluatethe results of gray-scale ultrasound, CEUS and methylene blue stainingdetecting SLN and to explore the value of contrast-enhanced ultrasonographyfor the detection of sentinel lymph node in breast cancer.Results:1. A total of 39 lymph nodes were resected for pathologic examination, of which, 30 were positive and the other nine, negative. A total of 35 lymphnodes were detected with gray-scale ultrasound, of which, four lymph nodeswere not successfully detected. Under the two-dimensional ultrasound, themetastatic lymph nodes were observed to be enlarged and their shapes areround. There was statistically significant differences (P＜0.05) in longitudinaland transverse diameter between the malignant and benign lymph nodes.However, there was no statistically significant differences (P＞0.05) invascular RI between the malignant and Benign lymph nodes. The detectionaccuracy of SLN by gray-scale ultrasound was 77% (27/35), sensitivity was76% (22/29) and specificity was 83% (5/6).2. The whole process of contrast agent from the tumor to the lymph tubeflow out to sentinel lymph node can be real-time displayed by using CEUS. Atotal of 35 lymph nodes were injected with ultrasound contrast agents, thedetection rate was 90% (35/39). The enhance types of malignant nodes weretypeⅡ,ⅢandⅣ,mainly in non-uniform enhancement and no enhancementtype, whereas those of non-metastatic lymph nodes were typeⅠ,ⅡandⅣ.The detection accuracy of SLN by CEUS was 83% (29/35), sensitivity was97% (28/29), specificity was 17% (1/6). False positive rate was 83% (5/6) andFalse negative rate was 3% (1/29).3. The number of lymph nodes stained by methylene blue was 32 whilethat of the non-stained lymph nodes was 7. The detection rate of SLN by bluedye staining was 82% (32/39), detection accuracy was 74% (29/39),sensitivity was 87% (26/30), specificity was 33%(3/9), False positive rate was67% (6/9) and False negative rate was 13% (4/30). Although the detectionrate of SLN by CEUS was higher than that by blue dye test, there was nostatistically significant differences (P＞0.05) between them. 4. There was no statistically significant differences (P＞0.05) indetection accuracy, sensitivity and specificity among the gray-scaleultrasound, CEUS and blue dye staining.Conclusion:1. The enhance types of malignant nodes were typeⅡ,ⅢandⅣ,mainly in non-uniform enhancement and no enhancement type, whereasthose of non-metastatic lymph nodes were mainly typeⅠ,ⅡandⅣ.Sonogram had a certain overlap of benign and malignant lymph nodes.2. CEUS can be used for real-time observing both lymphatic perfusionand lymph node metastasis, and for non-invasive positing SLN. It has thepotential ability to determine lymph node metastases.3. CEUS had similar detection rate, accuracy and sensitivity to blue dyestaining. It is suggested that the CEUS-guided method using SonoVue may bea novel useful mothod for SLN identification.