Fine needle aspiration of an intrathyroidal parathyroid carcinoma mimicking a primary thyroid anaplastic carcinoma: A case report with review of the literature

Intrathyroidal parathyroid carcinoma is an uncommon malignancy. A 46-year-old male presented with a left neck mass. Computed tomography (CT) scan revealed a hypodense mass in the left thyroid lobe along with evidence of metastatic lymphadenopathy. Aspiration of the left thyroid nodule was performed, and a diagnosis of malignancy was rendered, favoring a primary anaplastic carcinoma. Based on the cytologic diagnosis, the patient underwent a total thyroidectomy. Before the surgery, intact parathyroid hormone (PTH) and calcium level (PTH = 78 pg/mL; Calcium = 10.6 mg/dL) were found to be minimally elevated. On gross examination, a 3.2 cm mass within the left inferior thyroid lobe was seen. Histopathologic examination and ancillary studies supported the diagnosis of a parathyroid carcinoma. We, hereby present, an exceedingly rare presentation of an intrathyroidal parathyroid carcinoma with only minimal elevation of PTH and calcium, mimicking a primary anaplastic thyroid carcinoma on cytologic examination.