Thyroid gland
Congenital anomalies
Ectopic thyroid tissue

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

Revised: 5 July 2016, last major update February 2016

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

PubMed Search: Ectopic thyroid tissue [title]
Cite this page: Ectopic thyroid tissue. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/thyroidheterotopic.html. Accessed December 11th, 2016.
See also
Definition / General
  • Developmental abnormality characterized by the presence of thyroid tissue in any location other than its normal anatomic position
  • First well documented case was reported by Hickman in 1869 (AMA Arch Otolaryngol 1953;57:60)
Terminology
  • Synonyms:
    • Heterotopic thyroid, accessory thyroid, aberrant thyroid rests, choristoma
    • Wolfler's gland (cervical accessory thyroid), struma cordis (cardiac thyroid)
  • Types:
    • Sole / total ectopia vs. accessory thyroid (partial, associated with orthotopic thyroid)
    • Single or multiple (dual, triple, etc.)
    • Gross vs. microscopic
    • True vs. mimickers (metastasis, parasitic nodule, see Differential Diagnosis)
Epidemiology
  • The most frequent form of thyroid dysgenesis, accounting for ~50% of cases (Endocr Rev 2004;25:722)
  • Several hundred cases of ectopic thyroid have been reported
  • Prevalence in general population is 1 per 100,000 to 300,000 people
  • Prevalence in population with thyroid disease is 1 per 4,000 to 8,000 (Thyroid 2007;17:1117); however intense imaging screening yields up to 2% of ectopic thyroid in patients with thyroid disease (Arch Endocrinol Metab 2015 Aug 28 [Epub ahead of print])
  • Autopsy studies suggest that 7 - 10% of adults may have remnants of thyroid tissue along the path of thyroid descent (J Pathol 1970;102:239)
  • F:M = 3 - 4:1
  • May occur at any age, from 5 months to eighth decade, but is most common at younger ages (Hormones (Athens) 2011;10:261)
Sites
  • The target area for thyroid heterotopia lies along the track of medial anlage descent between the base of tongue and the normal thyroid location; a wider region can be defined as the Wolfler area, spanning from the edges of the mandible through the neck to the aortic arch (Nikiforov: Diagnostic Pathology and Molecular Genetics of the Thyroid, 2nd Edition, 2012)
  • Sites in descending order of frequency:
  • Distant sites are rare, categorized in Case Reports
  • Thyroid tissue in ovary (struma ovarii) represents a component of teratoma, sometimes in the absence of other tissues (monodermal teratoma)
Diagrams / Tables

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Thyroid descent

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Locations

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Accessory thyroids

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Ectopic thyroid, neck and chest

Pathophysiology / Etiology
  • Thyroid anlages may descend too slow or fast, and develop ectopia above or below normal thyroid position
  • Heart, large vessels and thymus originate very close to the primordial thyroid, and attachment of thyroid tissue may occur before their caudal migration
  • Developmental anomalies of the foregut may explain ectopia in the thorax and upper gastrointestinal tract (Nikiforov: Diagnostic Pathology and Molecular Genetics of the Thyroid, 2nd Edition, 2012)
  • Aberrant thyroid tissue in the submandibular and lateral neck regions could originate from a defective lateral thyroid component that cannot migrate and fuse with the median thyroid anlage (Endocr Rev 2004;25:722)
  • Heterotopic differentiation (heteroplasia, transdifferentiation) of uncommitted endodermal cells may hypothetically explain the presence of ectopic thyroid tissues in distant locations (Thyroid 2003;13:503)
  • Mutation in the genes of thyroid specific transcription factors TTF1, TTF2 (FOXE1) and PAX8 may be involved in abnormal migration of the thyroid, as shown in animals (Nat Genet 1998;19:395)
    • However, no mutation in known genes has so far been associated with the human ectopic thyroid
  • Rarely, familial thyroid heterotopia occurs (Thyroid 1992;2:325)
Clinical Features
Diagnosis
  • Thyroid cancer metastases should always be considered and excluded before accepting the diagnosis of ectopic thyroid
  • Imaging:
    • Radionuclide imaging with technetium-99m pertechnetate, iodine-131 or iodine 123
    • CT and MRI
    • Ultrasonography with color Doppler
  • FNA
Laboratory
  • Hypothyroidism (low T3 and T4, high TSH) occurs frequently
  • The inability to image the normal gland combined with a normal serum thyroglobulin may suggest an ectopic thyroid
Radiology Description
  • Scintigraphy: radioisotope tracer uptake in the area other than normal thyroid location (background from salivary glands should be considered)
  • Ectopic thyroid tissue has a characteristic uniform high attenuation on non contrast CT, while on MRI it shows an elevated signal on T1- and T2-weighted images compared with the surrounding musculature (Int J Surg 2014;12:S3)
  • Sonography: echotexture of thyroid tissue; usually isoechogenic, with regular margins, rare cystic degeneration, and without calcification (Arch Endocrinol Metab 2015 Aug 28 [Epub ahead of print])
Prognostic Factors
  • Prognosis is good: there is a very low chance of recurrence after surgical excision
Case Reports
Treatment
  • Asymptomatic euthyroid patients do not usually require therapy, but are kept under observation
  • Mild hypothyroidism is corrected by thyroid hormones
  • Radioiodine ablation is indicated for patients who are symptomatic or unresponsive to medical treatment (BMJ Case Rep 2015;2015:bcr2015210455)
  • Surgical excision is indicated for severe obstructive symptoms, bleeding, ulceration, cystic degeneration or malignancy (Thyroid 2007;17:1117)
  • It is important to determine the presence of an orthotopic thyroid gland before removing ectopic tissue to avoid hypothyroidism, because the ectopic gland may be the only functional thyroid (Hormones (Athens) 2011;10:261)
  • Auto-transplantation may help retain some degree of thyroid function
Clinical Images

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Neck ultrasound

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Neck CT

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Radionuclide scan

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Head MRI

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Chest CT

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Abdominal MRI

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Intracardiac thyroid

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Neck mass

Gross Description
Gross Images

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Submental mass

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Ectopic thyroid, lateral neck

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Intratracheal thyroid tissue, hyperplasia

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Mediastinal mass

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Intracardiac mass

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Cystic mass, adrenal gland

Micro Description
Micro Images

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Benign conditions

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Ectopic vs. orthotopic thyroid

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Posterior mediastinal mass

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Adrenal mass

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Adrenal mass, IHC

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Adenoma, ectopic thyroid

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PTC arising in ectopic thyroid

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Anaplastic carcinoma

Virtual Slides
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Thyroid rest, Case 2

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Ectopic thyroid tissue, Case 4

Cytology Description
  • Microfollicular aggregates and colloid (IRCMJ 2009; 11:100)
  • Additional findings may reflect pathological conditions of thyroid tissue, e.g. abundant lymphocytes (thyroiditis) or atypical cells with nuclear grooves and inclusions (papillary carcinoma)
Cytology Images

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Follicular cells

Positive Stains
Molecular / Cytogenetics Description
  • Absence of thyroid cancer related molecular alterations (BRAFV600E, N-RAS, H-RAS, K-RAS) in benign appearing ectopic thyroid tissue (Int J Surg Pathol 2015;23:170)
Differential Diagnosis
  • If any morphologic signs of malignancy are identified, then diagnosis is metastatic papillary thyroid carcinoma until proven otherwise
    • Clues to malignancy: classic architectural and cytomorphologic features of papillary carcinoma, with fibrotic response (desmoplasia) of surrounding tissue
    • Features against malignancy: separate blood supply of the ectopic gland from extra-cervical vessels, no personal history of malignancy, and normal or absent orthotopic thyroid with no history of surgery (Ann Thorac Cardiovasc Surg 2007;13:122)
    • Metastasis from ectopic thyroid carcinoma may also be considered
  • Benign mimickers of thyroid ectopia:
    • Cystically dilated non-thyroid glands with flattened epithelium and inspissated secretions
    • Parasitic nodule
    • Mechanical implantation outside gland due to surgery or trauma: history of neck surgery
    • Retrosternal goiter
    • Teratoma with thyroid component
  • Differential diagnosis in rare sites depends on the location
  • Accidental finding of thyroid follicles in unusual site may pose a concern about specimen contamination by tissue from an unrelated case ("floater"), which can be resolved by genetic fingerprinting (Hum Pathol 2007;38:378)