Background: Thyroid ectopia refers to a congenital disease with abnormal descending of the thyroid gland. The most common subtype is lingual thyroid ectopia. Sublingual and submental thyroid ectopia are much less common. It may also be found in other neck locations and distant positions .70%-90% of patients with ectopic thyroid do not have eutopic thyroid tissue. It is necessary to distinguish ectopic thyroid from other causes of neck masses. Case Presentation: A 18-year-old man was referred for the evaluation of a palpable mass in the submental region. On biochemical examination, the thyroid function tests were normal while receiving levothyroxine therapy. Ultrasonography revealed a mass measuring 4.2 × 2.7 × 2.6 cm in the submental region. The thyroid scan did not show any uptake in the thyroid region. A zone of the tracer activity was noted in the central neck, compatible with the palpated mass in the submental region. CT images showed a hyperdense soft tissue in the submental region, too. Conclusion: Thyroid ectopia is a rare condition and it is often accompanied by hypothyroidism. Ectopia often occurs in lingual and sublingual locations, and submental one is less common. Thyroid scintigraphy is the best imaging modality for the detection of thyroid ectopia. For precise localization, the CT scan correlation may be needed.

Keywords: Thyroid ectopia, submental, thyroid scintigraphy, case report.