ABSTRACT
ABSTRACT Ectopic thyroid tissue is rare in the general population and more prevalent in people who have existing thyroid disease. Common anatomical sites of ectopic thyroid tissue include the lateral cervical region, thyroglossal duct, mediastinum, lingual, sublingual, and submandibular region. Intrathymic ectopic thyroid tissue is exceedingly rare. The purpose of this report is to describe one such case in a 52-year-old African-American female with Graves' disease. The patient presented for a physical exam and follow-up. During the exam, an incidental mediastinal mass was discovered, which was evaluated by imaging studies and subsequently was resected. Histologically, the mass was composed of variable-sized thyroid follicles lined by a monolayer of cuboidal to columnar follicular epithelial cells and filled with eosinophilic colloid, surrounded by a rim of unremarkable compressed thymic tissue.