Oral cavity & oropharynx

Developmental anomalies

Lingual thyroid



Topic Completed: 1 February 2016

Minor changes: 25 October 2021

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: Lingual thyroid [title]

See also: Ectopic thyroid tissue

Andrey Bychkov, M.D., Ph.D.
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Cite this page: Bychkov A. Lingual thyroid. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/oralcavitylingualthyroid.html. Accessed October 28th, 2021.
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 prelaryngeal location
  • 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
  • Most lingual thyroids are asymptomatic
  • Symptomatic lingual ectopia is often manifested in women during puberty, pregnancy or menstruation
  • Most common symptoms are dysphagia, dyspnea and upper airway obstruction; other symptoms are foreign body sensation, pain, hemoptysis, dysphonia, snoring and sleep apnea (Endocr Pract 2016;22:343)
  • In more than 75% of patients, orthotopic thyroid is absent (total migration failure) and lingual thyroid represents the only thyroid tissue; as a result, 70% of patients with symptomatic lingual thyroid are hypothyroid; hyperthyroidism is exceptionally rare (Int J Surg 2014;12:S3)
  • Malignant neoplasms may arise in up to 1% of lingual thyroids; 50+ cases have been reported (J Clin Endocrinol Metab 2011;96:2684)
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)
Radiology images

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CT and laryngoscopy

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SPECT / CT



CT scan:
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Distinct margins

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Lingual thyroid

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Well defined mass

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Aberrant thyroid tissue

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48-year-old white female with obstructive lingual thyroid



MRI:
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Axial MRI: lingual thyroid

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38 year old female



Radionuclide scan:
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Scintigraphy with Tc-99m

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Tc99m pertechnetate planar image

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99mTcO4 radionuclide thyroid scan

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Thyroid scintigraphy



Angiography:
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External carotid artery angiogram

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Ectopic thyroid

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Carotid arteriography

Prognostic factors
Case reports
Treatment
  • Small lesions without symptoms usually require no therapy
  • Nonsurgical 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
    • Autotransplantation of pieces of lingual thyroid into the neck soft tissues may be considered
Clinical images

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Tongue mass:


Endoscopy:
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Flexible and rigid

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Swelling



Lingual thyroid in surgery:
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Exposed tumor

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Intraoperative photograph and surgical specimen

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

Microscopic (histologic) 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
  • 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)
Microscopic (histologic) images

Contributed by Andrey Bychkov, M.D., Ph.D.

Enlarged thyroid follicles



AFIP images
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Resembles malignancy



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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 (BRAF V600E, NRAS, HRAS, KRAS) are absent in benign appearing ectopic thyroid tissue (Int J Surg Pathol 2015;23:170)
Videos



Differential diagnosis
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