Discrimination of axillary metastatic from nonmetastatic lymph nodes with PROPELLER diffusion‐weighted MR imaging in a metastatic breast cancer model and its correlation with cellularity

AbstractPurpose:To assess the accuracy of apparent diffusion coefficient (ADC) in the differentiation of axillary metastatic from nonmetastatic lymph nodes in rabbits with metastatic breast cancer and to determine the relationship between the ADC and the cellularity of axillary lymph nodes of two different types.Materials and Methods:The axillary lymph node models were created by inoculating VX2 cell suspensions in the mammary glands of 30 female rabbits. Conventional MR imaging and multi‐shot fast‐spin‐echo PROPELLER DW imaging were performed approximately 4 weeks after successful inoculation. Images of axillary lymph nodes were analyzed with regard to size and ADC. Differences in the forementioned criteria between the two types of lymph nodes were assessed with reference to histopathologic findings. Cellularity was correlated with the ADC in all selected axillary lymph nodes.Results:A total of 41 axillary metastatic and 29 inflammatory lymph nodes were successfully isolated. The size‐based criteria showed no significant difference between the malignant and inflammatory lymph nodes (Ps > 0.05); however, the ADC of metastatic nodes was significantly lower than that of inflammatory nodes (P < 0.001). There was a significant inverse correlation between the ADC and cellularity (r = −0.674; P < 0.001) regardless of their different tissue types.Conclusion:DW imaging is a new promising functional technique for differentiating metastatic from inflammatory lymph nodes. Furthermore, cellularity has a significant influence on the ADC in both malignant and benign lymph nodes. J. Magn. Reson. Imaging 2012;36:624–631. © 2012 Wiley Periodicals, Inc.