MON-466 Dual Ectopic Thyroid with Normally Located Thyroid Gland in a Patient Presenting with Subclinical Hypothyroidism: A Case Report

Abstract Background: Ectopic thyroid involves the presence of thyroid tissue in sites other than its normal anatomic location. Dual ectopic thyroid with normally located thyroid gland is extremely rare with only a few cases reported in the literature. Clinical Case: A 24-year-old female presented to the clinic with subclinical hypothyroidism (TSH of 10.54 uIU/ml [ref, 0.27–4.2] and free T4 of 12.96 pmol/L [ref, 12–22]). She noted a gradually enlarging submental mass during the preceding year, which had been present since her adolescent years. Examination was notable for a 2-cm firm, non-tender mass at the submental region that slightly moved with deglutition. The thyroid was not palpable in its normal location. The relaxation phase of the deep tendon reflex was prolonged. Repeat laboratory testing showed persistently elevated TSH of 13.3 uIU/ml and normal free T4 of 13.39 pmol/L. TPO antibody was normal. Thyroid ultrasonography showed a hypoplastic thyroid measuring 2.7 x 0.7 x 0.4 cm on the right and 3.0 x 0.7 x 0.4 cm on the left. A well-circumscribed complex nodule measuring 2.7 x 3.2 x 2.1 cm was noted on the submental region corresponding to the patient’s submental mass. Computed tomography of the neck with contrast showed two hyperdense foci - measuring 3.0 x 2.4 cm at the submental region and 1.4 x 1.2 cm at the base of the tongue. No enhancing thyroid tissue was seen anterior to the thyroid cartilage. 99mTechnetium-pertechnetate scan showed absent focal tracer uptake in the anterior neck and thorax. There were foci of increased tracer activity in the submental and lingual regions. Ultrasound-guided biopsy of the submental area showed cytomorphologic features of a colloid nodule with cystic degeneration (Bethesda Category II). The patient was started on levothyroxine and remained biochemically euthyroid afterwards. The submental neck mass reduced in size. Conclusion: Dual ectopic thyroid with normally located (eutopic) thyroid gland could present with subclinical hypothyroidism. There is no single diagnostic modality that would best identify dual ectopic thyroid; thus, thyroid scan, ultrasonography, CT scan and biopsy are recommended to be used complementarily. For patients with dual ectopic thyroid and hypothyroidism, levothyroxine replacement is recommended to reduce the size of ectopic thyroid and render the patient euthyroid.