Oral cavity
Congenital anomalies
Lingual thyroid

Author: Andrey Bychkov, M.D., Ph.D. (see Authors page)

Revised: 2 March 2016, last major update February 2016

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Lingual thyroid [title]

Definition / General
  • Developmental anomaly in which ectopic thyroid gland is located at the base of tongue
  • Tongue is the most common site for total thyroid ectopia
  • First reported by Hickman in 1869 (AMA Arch Otolaryngol 1953;57:60)
Epidemiology
Sites
  • Most cases arise superficially or submucosally along the midline of base of the tongue between foramen cecum and epiglottis
  • Sublingual types (body of the tongue) are rarer, and may be suprahyoid, infrahyoid or at the level of the hyoid bone
Pathophysiology / Etiology
  • Failure of thyroid gland to descend from the foramen cecum to its normal pre-laryngeal location
  • The pathogenesis is unclear, but there are speculations that maternal antithyroid immunoglobulin may stop thyroid gland descent (Barnes: Surgical Pathology of the Head and Neck, 3rd Edition, 2008)
  • Hypothyroidism is commonly seen in patients with lingual thyroid, and some have hypothesized that lingual thyroid is a hyperplastic physiologic response by small thyroid remnants in the tongue to a low thyroid hormone level
  • Mutation in the genes of thyroid specific transcription factors TTF1, TTF2 (FOXE1) and PAX8 might be involved in thyroid arrest in tongue, as was shown in animals (Nat Genet 1998;19:395); however, no mutation in known genes has so far been associated with the human ectopic thyroid
Clinical Features
Diagnosis
  • Radionuclide scan with technetium or radioiodine
  • CT, MRI and angiography are important for the preoperative assessment of patients
  • FNA helps to differentiate benign from neoplastic conditions
  • Incisional biopsy is discouraged due to risk of complications, e.g. infection, necrosis or hemorrhage (Wenig: Atlas of Head and Neck Pathology, 3rd Edition, 2015)
Laboratory
  • Hypothyroidism (low T3 and T4, high TSH)
Radiology Description
  • MRI is useful in estimating extent of a lesion, because it can clearly distinguish thyroid tissue (low-intermediate T2 signal) from the tongue muscle (Hormones (Athens) 2011;10:261)
Prognostic Factors
Case Reports
Treatment
  • Small lesions without symptoms usually require no therapy
  • Non-surgical treatment includes thyroid hormone and radioiodine ablation to induce tissue regression (Int J Surg 2014;12:S3)
  • Major indications for surgical excision are airway obstruction and repeated significant hemorrhage
    • Transoral robotic surgery (TORS) is the most advanced surgical technique (Thyroid 2013;23:466)
    • Most patients with lingual thyroid have no other thyroid tissue, and acute hypothyroidism may occur after surgical removal
    • Auto-transplantation of pieces of lingual thyroid into the neck soft tissues may be considered
Clinical Images

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CT and laryngoscopy

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SPECT / CT



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Flexible and rigid

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Swelling



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Distinct margins



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Gross Description
  • Midline of base of tongue, usually between circumvallate papillae and epiglottis
  • Dome shaped, soft to firm mass with smooth surface, rarely ulcerated
  • Several mm to several cm in size (mean 2 - 3 cm)
  • Red, smooth to lobulated to nodular, either well or ill defined on sectioning
Gross Images

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Excised specimen

Micro Description
  • Thyroid tissue appears normal, with normofollicular and microfollicular patterns
  • Follicular cells are benign in appearance, without nuclear features of papillary carcinoma
  • Thyroid tissue usually grows between skeletal muscle and minor salivary glands of tongue, which may simulate tumor invasion
  • Circumscribed and encapsulated arrangement is rare
  • The diagnosis of primary thyroid carcinoma in a lingual site requires vascular invasion, unequivocal infiltration with desmoplastic response or metastasis in the absence of another primary site (Endocr Pathol 2002;13:353)
Micro Images

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Resembles malignancy



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Beneath squamous epithelium, tongue

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With skeletal muscle

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Thyroid follicles

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Papillary thyroid carcinoma
in lingual thyroid

Virtual Slides
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Lingual thyroid with follicular carcinoma

Cytology Description
Cytology Images

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Follicular cells

Positive Stains
Molecular / Cytogenetics Description
  • Mutations typical for thyroid cancer (BRAFV600E, N-RAS, H-RAS, K-RAS) are absent in benign appearing ectopic thyroid tissue (Int J Surg Pathol 2015;23:170)
Videos



Differential Diagnosis