FRI691 Intrathyroidal Parathyroid Adenoma With Congenitally Absent Contralateral Thyroid Lobe Treated With Thermal Ablation

Abstract Disclosure: L. Bilandzic: None. L. Bilandzic: None. H. Korkusuz: None. We present a rare case of primary hyperthyroidism with ectopic adenoma located in the right thyroid lobe with congenitally absent left thyroid lobe which was treated with thermal ablation. A 60-year-old woman was referred to endocrinology clinic for further evaluation of her elevated total serum calcium of 11.4 mg/dL (reference range 8.5-10.5), elevated parathyroid hormone (PTH) level of 106 (10-60 pg/mL). Bone mineral densitometry showed a total T score of -2.9 in L1-L4. Other results were vitamin D 25-OH 30 ng/mL (ref. range 30 - 100), TSH 3.36 µIU/mL (ref range 0.4-5.0), eGFR 83 (normal > 59 mL/min/ 1.73 m²). She was asymptomatic and had no history of kidney stones. Other causes of hypercalcemia were refuted. Given the osteoporosis in her lumbar spine, parathyroid localization and surgery were suggested. Thyroid and parathyroid sonography demonstrated a solid hypoechoic nodule in the right thyroid lobe, 12x10x11mm, with smooth margins, no calcifications, classified as ACR TI-RADS T4. Left thyroid lobe was not appreciated and was considered to be congenitally absent since the patient did not have a history of a previous thyroid resection. Further localization studies (99mTc Sestamibi parathyroid scintigraphy and 4D-CT of the neck) did not reveal any other possible candidates for parathyroid adenomas. Eventually, a fine needle aspiration of the nodule in the right thyroid lobe was performed. PTH needle wash showed a PTH value of 633 pg/mL whereas the PTH value ≥ 100 pg/mL is suggestive of the presence of PTH secreting tissue. Given the thyroid anatomy found with this patient, a right lobe hemithyroidectomy would result with a permanent substitution dependent hypothyroidism. As an alternative, thermal ablation was presented as a treatment option for which the patient opted. She underwent the procedure in local anesthesia. Sonographic imaging of the adenoma was followed by the percutaneous insertion of the coagulation electrode. The utilized high frequency ablator was used with an output of 9 to 40 W and a frequency of 470 ± 10 kHz. There were no complications developed during or after the procedure. Two weeks after the thermal ablation, PTH level was measured at 55 pg/mL, total serum calcium at 9.5 mg/dL, TSH 1.01 µIU/mL. Sonography showed a hyperechoic nodule at the former location of the parathyroid adenoma, which was evaluated as a scar tissue. Three months after the procedure total calcium was at 9.3 mg/dL, PTH at 58 pg/mL, hence no biochemical evidence of pHPT. This is a rare case of ectopic parathyroid adenoma located in the thyroid gland with hemi agenesis of the contralateral lobe. A minimally invasive thermal ablation was performed with the goal of inactivation of the adenoma and preserving the euthyroid function. Presentation: Friday, June 16, 2023