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Detection of Small Inflammatory and Metastatic Lymph Nodes in Rabbits by Sonography

Evaluation With the Resistive Index Ratio

Department of Ultrasound in Medicine, Shanghai Jiaotong University Affiliated Sixth People’s Hospital, Shanghai, China.

Address correspondence to Steven Bing Hu, MD, Department of Ultrasound in Medicine, Shanghai Jiaotong University Affiliated Sixth People’s Hospital, 200233 Shanghai, China. E-mail: binghu59{at}hotmail.com

Objective. The aim of this prospective study was to determine whether the resistive index (RI) ratio based on high-resolution spectral Doppler sonography would be useful in the differential diagnosis of small inflammatory and metastatic lymph nodes in rabbit models. Methods. The infected and metastatic lymph node models we used were created by subcutaneously inoculating methicillin-susceptible Staphylococcus aureus and VX2 tumor cells respectively into the left hind limbs of 10 New Zealand White rabbits. High-resolution sonography was performed to investigate the popliteal fossa lymph nodes 2 weeks after the inoculation. The sizes, long-/short-axis ratios, and RI ratios (defined as the value of the peripheral RI relative to the central RI) of the nodes were evaluated with sonography and then compared with the histopathologic findings. Results. No statistical differences were found between the volumes (mean ± SD, 104 ± 41 versus 87 ± 24 mm³; P > .05) and the long-/short-axis ratios (1.97 ± 0.28 versus 2.03 ± 0.26; P > .05) of 15 inflammatory and 14 metastatic lymph nodes. On spectral Doppler sonography, the RI ratio was higher in the metastatic lymph nodes than in the inflammatory lymph nodes. With an RI ratio higher than 1.2 as a diagnostic criterion for a metastatic lymph node, the sensitivity, specificity, and positive and negative predictive values of sonography were 71% (10/14), 80% (12/15), 76% (10/13), and 75% (12/16), respectively, with an area under the receiver operating characteristic curve value of 0.824. Conclusions. This experimental study confirms that RI ratio changes based on high-resolution spectral Doppler sonography are associated with histopathologic changes of metastatic and inflammatory lymph nodes during the initial stage in rabbits.

Key Words: inflammatory • lymph nodes • metastatic • rabbit • resistive index

Abbreviations: Az, area under the receiver operating characteristic curve • HE, hematoxylineosin • L/S, long-/short-axis • MSSA, methicillin-susceptible Staphylococcus aureus • PI, pulsatility index • RI, resistive index • ROC, receiver operating characteristic