Longitudinal 3.0T MRI Analysis of Changes in Lymph Node Volume and Apparent Diffusion Coefficient in an Experimental Animal Model of Metastatic and Hyperplastic Lymph Nodes

Purpose: To perform a longitudinal analysis of changes in lymph node volume and apparent diffusion coefficient (ADC) in healthy, metastatic. and hyperplastic lymph nodes. Materials and Methods: Three groups of four female Copenhagen rats were studied. Metastasis was induced by injecting cells with a high metastatic potential in their left hind footpad. Reactive nodes were induced by injecting Complete Freund Adjuvant (CFA). Imaging was performed at baseline and at 2, 5, 8, 11, and 14 days after tumor cell injection. Finally, lymph nodes were examined histopathologically. Results: The model was highly efficient in inducing lymphadenopathy: subcutaneous cell or CFA inoculation resulted in ipsilateral metastatic or reactive popliteal lymph nodes in all rats. Metastatic nodal volumes Increased exponentially from 5-7 mm(3) at baseline to 25 mm(3) at day 14, while the control node remained 5 mm(3). The hyperplastic nodes showed a rapid volume increase reaching a plateau at day 6. The ADC of metastatic nodes significantly decreased (range 13%-32%), but this decrease was also seen in reactive nodes. Conclusion: Metastatic and hyperplastic lymph nodes differed in terms of enlargement patterns and ADC changes. Enlarged reactive or malignant nodes could not be differentiated based on their ADC values.