SUN-589 Ectopic Thyroid Tissue within the Strap Muscle: An Unusual Finding

Abstract

Ectopic thyroid tissue is an uncommon clinical finding of thyroid tissue in a location other than the normal position of the thyroid in the lower anterior neck. Most commonly, thyroid ectopia exists as a lingual thyroid at the base of the tongue or in other structures which are in close proximity to the thyroid, including the larynx, trachea, surrounding soft tissue and muscles, or within thyroglossal duct cysts. More broadly, thyroid tissue can be found within the Wolfler area, which is located from the inferior border of the mandible to the aortic arch. Less commonly, thyroid ectopia can be found in more distant sites. A 65-year-old female with a history of type 2 diabetes and a recently discovered multinodular goiter presented to our clinic for further evaluation. She has no family history of thyroid cancer or personal history of radiation exposure. Her TSH and free T4 were 0.59 ng/dL and 0.93 uIU/mL, respectively. Additionally, thyroid peroxidase antibodies were negative. A routine ultrasound exam revealed a nodular goiter with a dominant 4.8 cm right isoechoic low-risk thyroid nodule in addition to two separate 1 cm heterogeneous isoechoic masses located in the midline at the junction of the thyroid cartilage and hyoid bone. The masses did not contain discrete nodules. CT scan demonstrated the nodular thyroid gland, a 1.2 cm mass located anterior to the hyoid, and a 1.3 cm mass embedded in the left strap muscle without adenopathy. A nuclear thyroid scan demonstrated radioactive iodine uptake in both of these extrathyroidal masses confirming multiple sites of ectopic thyroid tissue. Fine needle aspiration was performed of the right 4.8 cm nodule and had a benign, Bethesda II, cytology. The patient notes pain when turning her head from the left to the right and has been, thus far, referred for surgical evaluation. Thyroid ectopia is a rare finding that, more commonly, exists in patients with underlying thyroid conditions. Once suspected, thorough evaluation, including a high-quality neck ultrasound in addition to cross-sectional images of the area from the mouth to the aortic arch, is indicated. If the nuclear scan confirms normal functional thyroid tissue, observation is indicated for future growth or nodule formation. If a nodule is found in the ectopic tissue or if a radioactive iodine uptake scan is not performed, then a fine needle aspiration should be considered so as to rule out the possibility of thyroid cancer or metastases. Surgery is not always necessary unless there is uncertainty of the diagnosis or if the patient is symptomatic. Rarely, thyroid ectopia can be found in unusual sites including within the strap muscle as illustrated in this case. Although mentioned in surgical textbooks, thyroid tissue within the strap muscles has not been reported in the recent literature; this finding is important for practicing endocrinologists to consider.