Submental Ectopic Thyroid in a Patient with an Orthotopic Thyroid Gland

Abstract

Ectopic thyroid is a rare clinical disease, with the majority of the patient presented with hypo-functional thyroid tissue and absence of orthotopic thyroid gland. During embryogenesis, the thyroid gland descends from the foramen cecum to its normal position located below the larynx and hyoid bone, anterior to the 2 nd , 3 rd , and 4 th tracheal cartilaginous rings. Any defect that occurs during this period will result in ectopic thyroid. Hence, ectopic thyroid is usually found along the course of the thyroglossal duct, laterally in submandibular glands and even in distant places such as mediastinum or very rarely in sub-diaphragmatic organs. However, the presence of an orthotoptic thyroid may lead some difficulties in the diagnosis of this disease; hence, fine-needle aspiration is recommended to avoid unnecessary operation provided the patient is asymptomatic.

Personalized Management of Malignant and Non-Malignant Ectopic Mediastinal Thyroid: A Proposed 10-Item Algorithm Approach

“…From the embryogenesis perspective, thyroid gland represents the first endocrine tissue that is developed during intra-fetal life. The thyroid primordium starts its development since weeks three to four of gestation, while its migration takes place between the weeks five and seven; the secretion of fetal thyroid hormones begins between weeks ten and twelve [12,13]. The transcription factors that play a role in thyroid development are TTF1 (thyroid transcription factor-1 or NKX2.1) and TTF2 (or Foxe1), PAX8 (paired-box gene), HHEX (hematopoietically expressed homeobox protein) and TSH (thyroid-stimulating hormone) receptor, and they may be involved in the ectopic presentation [7,11,[14][15][16].…”

“…The most common ectopic thyroid site is represented by the tongue (the lingual thyroid is involved in 90% of all ectopic cases; of note, the first ectopic thyroid tissue at this level was described in 1869 by Dr. Hickman in a newborn with rapidly fatal outcome due to respiratory obstruction) followed by various locations (that are called sublingual type [17]) such as submandibular [18], peri-tracheal, larynx, sub-diaphragmatic area [12], etc. Across these 10% of ectopic cases, the most uncommon sites that are only partially understood based on the embryogenetic perspective are at the gastrointestinal level, including the gallbladder [19], adrenal glands, ovaries (struma ovarii), lumbar/renal [19][20][21][22], axillary [23], mammary [24], supra-sellar and suprachiasmatic [25].…”