Thyroid gland
Congenital anomalies
Thyroglossal duct (TGD) cyst

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

Revised: 5 October 2016, last major update March 2016

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

PubMed Search: Thyroglossal duct cyst [title]

Related: Thyroglossal duct carcinoma

Cite this page: Thyroglossal duct cyst. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/thyroidthyroglossal.html. Accessed December 2nd, 2016.
Definition / General
  • The most common developmental anomaly of thyroid gland, and the most common congenital neck mass
  • Midline neck developmental anomaly due to persistence and cystic dilation of thyroglossal duct
  • Thyroglossal duct (TGD) is the embryonic tract characterized by the presence of epithelial lined remnants and heterotopic thyroid tissue
  • May appear as blind tubular structure in mid neck or as sinus tract connected to foramen cecum or suprasternal notch skin
Terminology
  • Synonyms: TGD anomaly, TGD remnant, thyroglossal or thyreoglossal, thyroglossal duct or thyroglossal tract
  • Sinus is a blind ending tract lined by granulation tissue leading deep inside from natural / normal epithelial surface, e.g. from cervical skin or foramen cecum to TGD cyst (the latter, even being epithelialized, is not considered as a normal postnatal structure)
  • Fistula is a communication between two normal epithelialized surfaces, e.g. between skin and oropharynx via TGD tract / cyst, which is extremely rare (Laryngoscope 2009;119:2345)
  • TGD fistula is often used erroneously to represent the discharging sinus
Epidemiology
Sites
  • Appears in midline neck anywhere along path of TGD, from foramen cecum in tongue base to suprasternal region
  • Most TGD cysts are connected to hyoid bone, which is excised during TGD excision (Sistrunk procedure)
  • Prevalence (J Pediatr Surg 1984;19:555, Int J Pediatr Otorhinolaryngol 2003;67:1285):
    • 75% thyrohyoid (between hyoid bone and thyroid cartilage)
    • 25% suprahyoid, including submental
    • 2 - 4% intralingual (base of tongue)
    • Rare sites: suprasternal, intrathyroid, mediastinal
  • TDG cysts may present lateral to midline in 10-20%, but never lateral to large neck vessels
  • Mainly deviate to the left, because levator glandulae thyroideae is ordinarily found to the left (Surg Clin North Am 1953:633)
  • Often in the region of thyroid cartilage which moves superficial cyst from the median
  • Can be dislocated due to inflammation/fibrosis or previous surgery (Int J Pediatr Otorhinolaryngol 2003;67:1285)
Diagrams / Tables

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Thyroglossal tract

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Thyroglossal duct cyst

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Management algorithm

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Sistrunk procedure

Pathophysiology / Etiology
  • During embryonic development, thyroid gland remains connected to the foramen cecum (floor of primordial pharynx) and hyoid bone by TGD; the duct gradually disappears by the 10th week of development
  • If involution fails, TGD remnants may persist anywhere along the pathway of thyroid descent
  • The only normal remnant of the duct is the pyramidal lobe of the thyroid gland, which is seen in about 40% of the population (Thyroid 2013;23:84)
  • Cystic dilation is a result of secretion from the lining epithelial cells
  • Inflammation of lymphoid tissue adjacent to the TGD (repeated respiratory infections) may stimulate the epithelial remnants of thyroglossal tract to undergo cystic changes (BJS 1925;12:561)
  • Sinus is formed secondary to trauma, inadequate surgery drainage or spontaneous rupture of infected TGD cyst, e.g. due to microbial contamination from oral cavity via foramen cecum
Clinical Features
  • Most patients are asymptomatic, with a slowly enlarging painless cystic mass in the midline anterior neck (perihyoid), 2 - 4 cm in size (Auris Nasus Larynx 2008;35:11)
  • On physical examination, the cyst can be soft or firm and move upward on swallowing or protrusion of tongue
  • Infected TGD cyst occurs in 30% of patients, who present with pain, local inflammation, sometimes with draining sinus or fistula (Semin Pediatr Surg 2006;15:70)
  • After radiation therapy for unrelated head and neck cancer, TGD may enlarge and undergo cystic transformation (AJNR Am J Neuroradiol 2009;30:800)
  • Lingual TGD cyst may cause dysphagia, choking and cough; in neonates, may cause feeding problems, respiratory compromise and even sudden death
  • Rarely (<1%), TGD may give rise to tumors, usually papillary thyroid carcinoma, but also benign follicular adenomas, including Hurthle cell adenoma
Diagnosis
  • Based on typical clinical manifestations supported by radiological findings and confirmed by postoperative histopathology
  • Ultrasound is the preoperative investigation of choice (Radiographics 2014;34:37):
    • Echogenic characteristics of TGD cyst are cyst location, relation to the hyoid bone and echotexture of thyroid gland
  • CT and MRI play a supplementary role to more accurately delineate anatomy of large cysts, and MRI may be utilized to define a residual fistulous tract in recurrent disease (Auris Nasus Larynx 2008;35:11)
Radiology Description
  • Ultrasound (Korean J Radiol 2015;16:419, Clin Radiol 2005;60:141):
    • Midline (just under the hyoid bone) well circumscribed anechoic cystic lesion in simple TGD cyst
    • Pseudosolid appearance, when the cyst contains a proteinaceous fluid, cholesterol crystals and keratin
    • Heterogeneous pattern with internal echoes in cases of previous infection or hemorrhage
    • Most pediatric TGD cysts have a pseudosolid appearance
    • True solid component suggests risk of TGD malignancy
  • CT with contrast shows a well delineated cystic lesion with capsular enhancement (especially in infected cysts), and its relation to hyoid bone (Indian J Surg 2011;73:28)
  • MRI demonstrates low signal intensity with T1 weighted sequences and high signal intensity with T2 weighted sequences which do not restrict diffusion; expansion and destruction of the cartilaginous structure of the hyoid (Radiographics 2014;34:37)
  • Scintigraphy potentially can detect functioning thyroid tissue in TGD (Thyroid 2007;17:341)
Radiology Images

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Neck ultrasound

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Neck CT

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Neck CT

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Scintigraphy

Prognostic Factors
  • Excellent prognosis after complete excision, even if carcinoma is present
  • Recurrence rate after Sistrunk procedure is less than 5%; however, if the central hyoid bone is not removed, TGD cyst may recur in 25% cases (Surg Gynecol Obstet 1949;89:727)
  • Risk factors for complications and recurrence are young age (<10 y.o.), lobulated, infected or ruptured cyst, skin involvement and failure to excise the midportion of the hyoid bone and the suprahyoid tract (Am J Surg 1986;152:602)
Case Reports
Treatment
  • Surgery is routinely recommended for all patients with TGD cysts
  • The treatment of TGD remnants, whether cyst or sinus / fistula, is a complete surgical excision using the Sistrunk procedure
  • Incision / draining or sclerotherapy is strictly discouraged
Clinical Images
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Neck mass

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TGD cyst in children

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Infected TGD cyst

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Fistula

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Intra-operative

Gross Description
  • The thyroglossal duct is a continuous tract from the base of tongue, but occasionally is multiple and aborizing, with a dominant cyst and smaller cysts that are identified microscopically (J Pediatr Surg 1984;19:506, J Pediatr Surg 1991;26:766)
  • Cysts are unilocular or multilocular with rounded, smooth external surfaces
  • Cyst has a mean diameter of 2 cm, range 0.2 - 7 cm (J Am Coll Surg 2002;194:274, Endocr Pathol 2015;26:75), giant cysts >10 cm are also described (Ann Surg 1954;139:123)
  • Cystic content includes clear mucinous or viscous fluid / gel having a broad range of color (clear, yellow-tan, red-brown and gray-white) and degree of opacity; infected cysts contain purulent exudate
  • TGD is often firmly embedded in the surrounding strap muscles and soft tissues of the neck without a plane of cleavage around it
  • Sinus tract or fistula may have openings to pharynx or skin
  • Thyroid tissue is usually not grossly evident, but if present appears as a reddish-tan or reddish-brown focus (Nikiforov: Diagnostic Pathology and Molecular Genetics of the Thyroid, 2nd Edition, 2012)
  • The hyoid bone is part of the surgical specimen (since TGD is always attached to the hyoid) and should be examined for microscopic remnants of the cyst within the bone or immediately adjacent to it (Int J Pediatr Otorhinolaryngol 1998;44:47)
  • Gross Images

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    TGD cyst (AFIP)



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    In situ

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    TGD cyst after Sistrunk procedure

    Micro Description
    • Type of epithelial lining varies by site, and combinations of the types below can be seen in a single cyst (Head Neck Pathol 2013;7:50):
      • Ciliated pseudostratified columnar (respiratory) epithelium in lower neck, perhaps due to its close proximity to upper respiratory tract
      • Non-keratinizing squamous epithelium in higher neck (near tongue and foramen cecum), also can be of metaplastic origin in inflammatory settings
      • Stratified cuboidal epithelium at level of hyoid bone
      • Very often the cyst is denuded of epithelium, at least focally, which reflects epithelial damage by inflammation
    • Secondary inflammation is common, especially in sinus tract (J Pediatr Surg 1984;19:506):
      • Intense lymphocytic infiltration, rarely arranged into lymphoid follicles
      • Admixture of neutrophils (if the cyst is infected)
      • Granulation tissue and fibrosis
    • Thyroid follicles in the cyst/duct wall:
      • Found in 30-60%, with higher yield on serial sections
      • More common in infra- vs. suprahyoid remnants, on the right paramedian side (Ann Otol Rhinol Laryngol 2000;109:1135)
      • Seen in small irregular groups
      • Thyroid epithelium may be normal or rarely hyperplastic or neoplastic
      • Thyroid tissue often hidden by inflammation (Laryngoscope 2001;111:1002)
      • Absence of thyroid tissue does not exclude the diagnosis of TGD cyst
    • Mucous salivary-type glands can be found in the cyst wall, frequently in lingual and suprahyoid locations (Ann Otol Rhinol Laryngol 1996;105:996)
  • Occasional inclusions:
  • One study found that specimens clinically diagnosed as TGD cyst were classified based on histology as true cysts (50%), ducts without evidence of cysts (40%) and fibrous tracts (10%) (J Laryngol Otol 2000;114:128)
  • Micro Images
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    Courtesy of Dr. Andrey Bychkov:
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    Perihyoid cystic and arborized tubular structure

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    Perihyoid cystic structures

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    Thyroglossal duct penetrates hyoid bone

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    Denuded TGD, perihoid location

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    Variable epithelial lining

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    Ciliated vs squamous epithelium

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    Thyroid follicles under ciliated epithelium

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    Thyroid follicles of various size

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    Thyroid follicles embedded within skeletal muscles

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    Seromucous glands

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    Rupture of the cyst wall

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    Cyst rupture with
    cholesterol clefts,
    giant cells
    and siderophages
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    Thyroglobulin expression by thyroid follicles

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    Strong TTF1 expression



    Courtesy of Dr. Mark R. Wick:
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    Thyroglossal duct cyst



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    Epithelium

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    Papillary changes



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    Squamous epithelium

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    Pseudostratified

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    Cuboidal epithelium

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    Squamous stratified epithelium

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    Cyst wall

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    Epithelial lining

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    Respiratory epithelium

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    Thyroid follicles

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    Thyroglossal tract cyst

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    7 1/2 week embryo

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    Cyst wall

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    With mucocele

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    With ectopic parathyroid

    Virtual Slides
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    Thyroglossal duct cysts

    Cytology Description
    • Preoperative FNA is moderately sensitive but with many false negatives (Diagn Cytopathol 2005;33:365)
    • FNA smears are of low cellularity, with predominant inflammatory cells outnumbering epithelial cells, similar to branchial cleft cyst:
      • Macrophages, either foamy or hemosiderin laden
      • Mature lymphocytes and neutrophils (predominantly if the cyst is infected)
      • Squamous or ciliated columnar epithelium
    • Colloid is common, ranging from thick and fragmented to thin and watery
    • Admixture of cholesterol crystals
    • Thyroid tissue found in <10% of aspirates, likely due to deep embedding in the cyst wall
    Cytology Images
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    Courtesy of Dr. Andrey Bychkov:
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    Sparsely cellular aspirate
    with inflammatory cells
    and infrequent squames
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    Benign squamous cell
    in an inflammatory background
    composed of histiocytes, lymphocytes
    and scattered polymorphs


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    Squames

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    Neutrophils and macrophages

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    Epithelial sheet

    Negative Stains
    Videos



    Differential Diagnosis
    • Cystic lesions
    • Solid lesions
      • Lingual thyroid: resolved by clinical and radiological modalities, orthotopic thyroid is often absent
      • Pyramidal lobe of thyroid gland
      • Lymph node with reactive hyperplasia
      • Lipoma
      • Squamous cell carcinoma: atypical cells
      • Rare intrathyroidal TGD cysts can be confused with primary thyroid carcinoma
    • Histopathological diagnosis of TGD requires optimally evidence of respiratory/squamous epithelial lining and thyroid follicles, which sometimes can be difficult to find due to inflammation and fibrosis; in these situations, a diagnosis of developmental cyst with comment (favor TGD cyst or branchial cleft cyst, etc.) may be an option