Pre-contrast hyperattenuating metastatic lymph node on computed tomography due to iodide accumulation in a dog with thyroid carcinoma

An 11-year-old Bichon Frise presented with a right cervical mass. Computed tomography revealed a thyroid mass without significant lymphadenopathy; however, the caudal portion of the ipsilateral retropharyngeal lymph node exhibited marked hyperattenuation on pre-contrast images. Histopathology of this lymph node confirmed the presence of metastasis from thyroid adenocarcinoma. The caudal portion of the lymph node displayed dense tumor cells with abundant sodium/iodide symporter-positive cells. The observed hyperattenuation of the lymph node was presumed to result from iodide deposition associated with the metastasis of the thyroid tumor. This case suggests that even in the absence of lymph node enlargement, hyperattenuating lymph nodes should raise suspicion for metastasis in dogs with thyroid tumors. However, as this is a single case, further studies are needed to determine the broader applicability of this finding.