Intrathyroidal Parathyroid Carcinoma: Case Report and Literature Review.

Intrathyroidal parathyroid carcinoma (PC) is a rare malignancy that is usually difficult to diagnose. We present a case of a 31-year-old male with a history of hyperparathyroidism who was found to have intrathyroidal PC upon review of immunostains along with a review of the current literature. A systematic review of the literature utilizing the PubMed database identified 24 relevant, full-text articles. 25 cases were analyzed, including our own report. The case of a 31-year-old man with a history of hyperparathyroidism managed with subtotal thyroidectomy and subtotal parathyroidectomy who had persistent hypercalcemia and elevated parathyroid hormone. Abnormal radiotracer uptake was noted in the left thyroid gland. Neck exploration with left parathyroidectomy and revision thyroidectomy was performed. A candidate left inferior parathyroid was found within the left thyroid lobe remnant and identified as parathyroid carcinoma. Immunostains determined an intrathyroidal parathyroid carcinoma. The literature review shows the average presenting age was 50.9 years. 54.17% (CI, 43-82%) of affected patients are female. Right-sided thyroid involvement is seen in 54.17% (CI, 34-74%) of cases. The inferior aspect of the thyroid is involved in 66.67% of cases (CI, 53-89%). Intrathyroidal parathyroid carcinoma is a rare and challenging diagnosis due to similarities with other more common endocrine abnormalities. This review found that the inferior parathyroid is more likely to be located within the thyroid gland. Surgeons may consider aberrant anatomical locations, including intrathyroidal locations, for the inferior parathyroid glands.