SAT533 The Case of an Ectopic Thyroid Twin

Disclosure: A. Abu Limon: None. S.A. Aldasouqi: Consulting Fee; Self; Abbott Laboratories. P. Kachhadia: None. S. Khan: None. Introduction: Ectopic thyroid tissue is a rare but known developmental abnormality during the descent of the thyroid tissue from the floor of the foregut to its final location Infront of the trachea. The most frequent ectopic locations are the base of the tongue and anywhere along the course of the thyroglossal duct. It is very rare to have an ectopic thyroid tissue located in the mediastinum. It’s even more rare when the patient still has an almost normal thyroid gland in its usual location in the neck, and both are sizable and functional. Case Presentation: We are reporting the case of a 38-Year-old African American Female, who was involved in a car accident with non-critical injuries to her neck and chest area. She underwent a contrasted CT scan of her neck and chest that showed an anterior mediastinal mass towards the right at the level of the great vessels and arch, right paratracheal location overall measuring 6.0 x 4.6 x 4.5 cm. She was seen by Cardiothoracic surgery group and underwent Mediastinoscopy that confirmed a large firm to hard mass just inferior to the innominate artery was firmly adherent to the trachea as well as surrounding structures. Multiple biopsies showed thyroid tissue with focal mild chronic inflammation, benign. No atypia or malignancy is noted. Then, she was referred to our clinic for further evaluation. When interviewed, the patient denies any compressive symptoms (Shortness of breath, palpitations, chest pain or dysphagia). The patient has no personal or family history of thyroid disorders, including no thyroid cancer history. She has no Goiter on exam and no Pemberton sign is elicited. Laboratory work up was unremarkable including normal thyroid functions. Neck Ultrasound confirmed presence of a thyroid gland in its expected location, with Right Lobe Measurement: 5.04 x 1.70 x 1.47 cm Vol: 6.02 ml and Left Lobe Measurement: 3.94 x 1.25 x 1.21 cm Vol: 2.87 ml. We were keen to explore this matter further and ordered a thyroid uptake scan with 0.97 uCi iodine-123, that showed a 24-hour normal uptake of 27.4% at the thyroid bed and a separate substernal and RT paratracheal location uptake. Discussion: This patient has supplementary ectopic thyroid tissue in her mediastinum along with a normal thyroid gland in her neck. From the literature review and search, This is a very rare occurrence. The discussion with the patient is about the specific concern of the malignant potential of this ectopic thyroid and if surgical intervention is needed. The probability of cancer on ectopic thyroid tissue is less than 1% and when it occurs papillary carcinoma is the most common histology. Our patient has benign biopsy results and no signs nor symptoms related to this ectopic thyroid gland. The final decision is to not undergo surgery, but rather, a follow up with CT scan in 6 months. Presentation Date: Saturday, June 17, 2023