Thyroid Hemiagenesis, Ectopic Submandibular Thyroid Tissue, and Apparent Persistent Subclinical Thyrotoxicosis

Abstract

Ectopic thyroid tissue (ETT) is a rare embryological abnormality characterized by the occurrence of thyroid tissue in a site other than its usual location. Thyroid hemiagenesis (HA) is also a very rare abnormality in which one thyroid lobe does not develop properly during embryology. We report a patient with left HA, submandibular ETT, and persistent mildly suppressed serum thyrotropin (TSH). A 38-year-old female patient was admitted with complaints of sweating and palpitations. She had no symptoms of neck compression. Thyroid ultrasonography revealed heterogeneity and hypoechogenicity of the right lobe and absence of the left lobe, the latter being confirmed by computed tomography. There was no ETT in the neck. A thyroid Tc-99m pertechnetate scan demonstrated two distinct areas of radiotracer uptake, one in the right lobe of the thyroid gland and one in the right submandibular region and lobe, but no uptake in the left thyroid bed. The serum free triiodothyronine was 2.89 pg/mL (2.5-3.9 pg/mL), and the serum free thyroxine was 0.86 ng/dL (0.61-1.12 ng/mL). The serum TSH was 0.11 mIU/L (0.34-5.60 mIU/L). This may be the first reported patient with HA and submandibular ETT. The patient probably also had thyroiditis with mild intermittent thyrotoxicosis based on her suppressed TSH and ultrasonography imaging of the right thyroid lobe.