Erin N. Kishi, Shannon P. Holmes, Jeffrey R. Abbott, Nicholas J. Bacon
A 12-year-old dachshund dog was presented for persistent hypercalcemia and hyperparathyroidism despite bilateral parathyroidectomy. Magnetic resonance imaging of the head, neck, and cranial mediastinum identified an increased number of cranial mediastinal lymph nodes with heterogeneous signal intensity. Hypercalcemia and hyperparathyroidism resolved after surgery to remove multiple cranial mediastinal lymph nodes, one of which contained presumed metastatic parathyroid tissue. Hyperparathyroidism is characterized by elevated serum ionized calcium in the face of inappropriately normal or elevated serum parathyroid hormone (PTH) levels. The most common cause is a pathologic autonomously functioning parathyroid tumor (primary hyperparathyroidism) (1). Primary hyperparathyroidism due to parathyroid tumors is the third most common cause of hypercalcemia, making up about 13% of the cases of elevated ionized calcium in dogs (2). Most commonly, primary hyperparathyroidism develops as a result of a solitary parathyroid gland adenoma (73% to 86%), less commonly hyperplasia of 1 or more glands (11% to 16%), and rarely parathyroid adenocarcinomas (3% to 11%) (3,4). Parathyroid adenomas and carcinomas usually affect a single gland and are grossly similar in appearance. The other parathyroid glands are normal, atrophied or not grossly visible. A carcinoma is usually determined if there is capsular or vascular invasion by the abnormal parathyroid tissue, presence of mitotic figures within parenchymal cells, or fibrous trabeculae on histopathology (5). In humans, parathyroid adenocarcinoma is also rare and accounts for 4% of patients diagnosed with primary hyperparathyroidism (5). The purpose of this manuscript is to report a case of metastatic parathyroid adenocarcinoma found in a cranial mediastinal lymph node by magnetic resonance imaging (MRI) and confirmed by histopathology.