Introduction

Lymphotropic nanoparticle magnetic resonance imaging (LNMRI) utilizes ultrasmall paramagnetic iron oxide nanoparticles (USPIOs) for imaging of lymph nodes in patients afflicted with cancer. USPIOs are phagocytized by macrophages and then localized to lymph nodes where they create a susceptibility artifact on gradient echo MRI sequences. Infiltrative cancer cells in lymph nodes cause regions of effacement which prevents this, allowing for identification of disease. LNMRI has proven to be a highly accurate method of identifying metastatic lymph nodes in human medicine and has recently been investigated for veterinary patients.

Methods

Twenty dogs with head and neck tumors were imaged 48 hours after injection of USPIOs. Local lymph nodes were evaluated for presence of metastasis then subsequently extirpated. Imaging results were compared to histological analysis and the sensitivity and specificity of LNMRI calculated.

Results

There was a total of 20 dogs and 90 lymph nodes included in this study. Lymph nodes were treated as individual data points. There was a total of 73 lymph nodes that were non-metastatic and 17 metastatic. The overall sensitivity, specificity, and accuracy of LNMRI was 69.2%, 93.1%, and 86.7% respectively. However, if dogs with mast cell tumors were excluded from analysis the sensitivity, specificity, and accuracy rose to 94.1%, 95.9%, and 95.6%.

Conclusions

LNMRI is an accurate way to determine the presence of lymph node metastasis in dogs with some types of head and neck tumors. However, LNMRI has only moderate accuracy in dogs with oral or mucocutaneous mast cell tumor.

Funding Information

Morris Animal Foundation Grant, Colorado State University College of Veterinary Medicine and Biomedical Sciences College Research Council Grant, and AMAG Pharmaceuticals all provided financial support for this project.