Lynch KC, Odintsov BM, O’Brien RT.
Introduction/Purpose: Conventional magnetic resonance imaging is widely utilized in veterinary medicine to critically evaluate soft tissue structures in disease states. Proton magnetic resonance spectroscopy CHMRS) is a non-invasive and non-ionizing technique, based on fundamental nuclear magnetic resonance principles, which is used to gain additional metabolic information from tissues of interest. 1HMRS is well described in the human medical literature, and is most frequently utilized to evaluate tissues with questionable malignant transformation. Differentiation of neoplastic tissue from surrounding normal tissue is dependent on alterations in cellular metabolism. Therefore, 1HMRS may be used to detect cancer in its earliest stages, at the cellular level. Increased levels of the choline metabolite have been extensively associated with malignancy across numerous tumor types and within tumor metastases. The goal of this study was to quantitatively evaluate choline levels within a population of malignant, reactive, and normal canine lymph nodes ex vivo.Methods: Peripheral, abdominal, or thoracic lymph nodes were collected intra- operatively or immediately post-euthanasia from canine patients. Lymph nodes were immediately flash frozen and stored at -80 degrees Celsius until the time of imaging in order to preserve tissue metabolites. High field (14T) 1HMRS was performed on each lymph node. Choline signal-to-noise ratios (SNR) were calculated and compared between the three groups. Histopathology was performed on all lymph nodes for confirmation of nodal status.Results: A total of 54 lymph nodes were collected (37 malignant, 8 moderately to severely reactive/lymphoid hyperplasia, 9 normal/mildly reactive) from a population of 19 dogs. The malignant population consisted of large cell lymphoma (13), T cell lymphoma (18), mast cell neoplasia (5), and thyroid carcinoma (1). A choline SNR>/2 was significantly associated with malignancy (P<0.001). The choline SNR was significantly higher in the malignant population than in both the normal (p<0.001) and reactive (p=0.001) populations. There was no significant difference in the choline SNR between the normal and reactive group (p=0.920). Overall, 1HMRS detected malignancy via elevation of the choline metabolite with a sensitivity, specificity, positive and negative predictive value of 80.4%,94.4%,97.4%, and 65.4% respectively.Discussion/Conclusion: With future in vivo studies, 1HMRS has the potential to improve the detection of primary and metastatic lymphadenopathy in veterinary oncology patients, and may be a useful addition to whole body MRI staging. The choline metabolite may be a useful metabolic marker for malignancy.