SAT198 Parathyroid Adenoma Masquerading As A Thyroid Nodule

Disclosure: A. Arida: None. M. Papaleontiou: None. N. Esfandiari: None. Background: The diagnosis of parathyroid adenomas using a neck ultrasound (US) can be challenging when not performed by an experienced radiologist. Additional methods of diagnosis have been implemented to distinguish the differential diagnosis of a nodule in the neck. Clinical Case: A 48-year-old woman with a history of type 2 diabetes, hypercalcemia, and kidney stones presented for evaluation of a lump in the neck of 5 years duration. Prior thyroid US showed a solid hypoechoic nodule superior to the left thyroid lobe measuring 2.2 x 1.2 x 1.1 cm with hypervascularity. Her first FNA biopsy of this nodule reported benign cytology 5 years ago. A parathyroid scintigraphy scan was negative. Repeat FNA biopsy of this nodule showed follicular lesion of undetermined significance (Bethesda category III). Surgical consultation was recommended but she decided to seek a second opinion. A repeat neck US identified a solid vascular 1.6 cm nodule along the anterior margin of the superior left thyroid lobe. Some vascularity was extending from the thyroid tissue into the nodule. It was noted that this may represent an extrathyroidal nodule or arise from the thyroid gland with a score of TIRADS 4. Laboratory tests confirmed primary hyperparathyroidism with an iPTH of 126 pg/mL (normal range, 10-65 pg/mL) and serum calcium of 10.9 mg/dL (normal range, 8.6-10.3 mg/dL). After normalizing vitamin D levels, these values remained elevated. A repeat FNA biopsy of this nodule showed evidence of intrathyroidal parathyroid tissue. Immunostains were performed on the cell block material from the FNA biopsy. Scattered groups of cells were positive for PTH while being negative for TTF-1. Further needle washout for iPTH measurement revealed an iPTH >2000 pg/mL confirming the diagnosis of a parathyroid adenoma. Parathyroid surgery was recommended as per guidelines. Discussion: Once primary hyperparathyroidism is confirmed, the localization of parathyroid adenoma is pursued by a neck US and/or parathyroid scintigraphy. Parathyroid glands are located in the superior poles and in the inferior poles of the thyroid gland but ectopic locations like retropharyngeal, intrathyroidal, and mediastinal are possible. Typical US appearance is oval, solid, well-circumscribed, homogenous, and hypoechoic compared to the thyroid tissue. The color Doppler shows that the blood supply enters at the center and distributes peripherally presenting a “vascular arch” pattern that helps differentiate them from other lesions such as tumors or lymph nodes where the distribution is more centralized. Further needle washout for PTH level can confirm the diagnosis of parathyroid adenoma. Once a parathyroid adenoma is confirmed, minimally invasive parathyroid surgery can be recommended if surgery is indicated. Conclusion: A needle washout for measuring PTH in an FNA biopsy sample should be recommended when it is unclear whether a nodule is a thyroid nodule or a parathyroid adenoma. Presentation: Saturday, June 17, 2023