BENIGN LYMPH-NODE HYPERPLASIA AND LYMPH-NODE METASTASES IN RABBITS - ANIMAL-MODELS FOR MAGNETIC-RESONANCE LYMPHOGRAPHY

OBJECTIVES. Experimental models of reactive lymph-node hyperplasia and lymph-node metastasis were developed for magnetic resonance imaging (MRI). METHODS. Reactive lymph-node hyperplasia was induced in 20 rabbits by injection of an egg-yolk emulsion intramuscularly in the hind limbs and subcutaneously in the flanks. In another 20 rabbits, lymph-node metastasis was induced by implantation of a squamous cell carcinoma (VX2 tumor) in one hind limb. Five rabbits remained untreated. Signal intensity and size of iliac medial and popliteal lymph nodes were investigated with T1-, T2-, and proton-density-weighted spin-echo sequences at 1.5 T. In addition, lymph-node activity and metastatic involvement were assessed histologically. RESULTS. Lymph nodes in untreated animals were small and difficult to visualize by MRI. After egg-yolk-induced reactive lymph-node hyperplasia, the enlarged nodes were well demonstrated by MRI. Implantation of VX2 tumors led to different degrees of lymph-node metastasis (micrometastasis, partial and complete metastatic permeation), depending on growth period and size of the primary tumor. In MR images, lymph nodes of untreated, stimulated, and tumor-bearing rabbits were not differentiable by signal intensity. CONCLUSION. Reactive lymph-node hyperplasia induced by interstitial egg-yolk injection and lymph-node metastasis secondary to implantation of VX2 tumors cannot be differentiated by standard MRI. Therefore, these models may serve for testing the efficacy of lymphographic techniques in MRI.