Thyroid gland
Congenital anomalies
Thyroglossal duct carcinoma

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

Revised: 23 February 2017, last major update March 2016

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Thyroglossal duct carcinoma [title]

Related: Thyroglossal duct cyst
Cite this page: Thyroglossal duct carcinoma. PathologyOutlines.com website. http://pathologyoutlines.com/topic/thyroidthyroglossalcarc.html. Accessed April 23rd, 2017.
Definition / General
  • Rare malignancy arising from thyroid follicular cells of TGD remnants, first described by Brentano in 1911 (Dtsch Med Wochenschr 1911;37:665)
  • TGD is the most common site for malignancy in ectopic thyroid tissue
  • The main type is papillary thyroid carcinoma; medullary carcinoma has not been reported, because C cells are absent in TGD
Terminology
  • Very recently, a new term of upper neck papillary thyroid carcinoma has been proposed to combine TGD cyst cancer, pyramidal lobe cancer and Delphian (prelaryngeal) lymph node metastasis, which are often difficult to distinguish (Laryngoscope 2016;126:1709)
Epidemiology
  • Carcinoma found in < 1% of TGD cysts (up to 5% - 7% in large referral centers), however the risk of this developing over time is probably underestimated due to the routine removal of TGD cysts in childhood (Semin Pediatr Surg 2006;15:70)
  • F:M = 2:1, mean age 40 years (range 6 to 84 years)
  • Pediatric cases are uncommon (< 15% of all TGD cancers), with mean age 12 years (Thyroid 2004;14:777)
  • Histopathology (J Clin Endocrinol Metab 2011;96:2684):
    • 90% papillary thyroid carcinoma, mainly classic variant, however follicular and tall cell variants are also reported (< 10%)
    • 5% squamous cell carcinoma, derived from the actual cyst lining
    • 2% - 3% follicular carcinoma
    • Rare cancers (anaplastic, mucoepidermoid, adenosquamous) and combinations
  • 250+ cases have been reported (Laryngoscope 2016;126:1709)
Pathophysiology / Etiology
  • Two opposing concepts of TGD carcinoma origin are metastatic and de novo (J Clin Endocrinol Metab 2011;96:2684)
  • Metastatic: TGD cancer represents a metastasis from an occult primary thyroid carcinoma:
    • Coincident orthotopic thyroid gland cancer, mainly papillary microcarcinoma, occurs in 30% - 60% of TGD cyst patients when thyroidectomy is performed (J Clin Endocrinol Metab 2013;98:458)
    • Benign tumors are described in TGD, which cannot be explained by metastatic theory
  • De novo: TGD cancer arises from TGD remnants, based on these observations:
    • TGD cancer may arise from thyroid follicles (found in roughly half of TGD remnants) in the same manner as any ectopic thyroid tissue, e.g. lingual, may transform to carcinoma
    • TGD carcinoma has peculiar features (age, pattern of nodal involvement) not typical for primary thyroid carcinoma
    • Coexisting thyroid carcinoma in TGD and orthotopic may have discordant histotypes (Virchows Arch 2014;465:67)
    • High rate of coincident carcinoma in orthotopic thyroid is consistent with the incidence of occult thyroid carcinoma found in autopsy studies of undiagnosed patients
    • Another component of TGD, particularly epithelial lining, does transform to squamous cell carcinoma
    • C cells are absent in TGD and so far no medullary carcinoma in TGD has been described
Clinical Features
  • Most TGD carcinomas are asymptomatic and are discovered by the pathologist on routine histologic evaluation
  • Clinically, no clear distinction between a benign cyst and malignancy can be made (Head Neck Surg 1982;5:134)
  • Cancer can be suspected based on:
    • Sudden growth of preexisting cyst, although there is no relationship between size or duration of the cyst and malignant change
    • Hard, fixed and irregular mass
    • The cyst is associated with enlarged cervical lymph nodes
    • There is a history of neck irradiation
  • Metastatic disease:
  • Coexisting occult carcinoma in normal thyroid gland found in 30% - 60% of TGD cyst cases with thyroidectomy (J Clin Endocrinol Metab 2013;98:458, Endocr Pathol 2015;26:75)
Diagnosis
  • Preoperative diagnosis of carcinoma in a patient presenting with TGD cyst is unusual
  • Routine workup is similar to that for TGD cyst, essentially neck ultrasound, which can be complemented by CT, MRI and FNAC
  • Criteria for diagnosis includes histopathological confirmation of thyroglossal remnants in a specimen with carcinoma, and normal thyroid gland (to exclude a metastasis from a primary lesion in the gland)
  • Fine needle aspirate of the cyst may be helpful in confirming the clinical suspicion (most efficient in adults), however FNA cytology has relatively low sensitivity, and intraoperative frozen sections are advocated as a more robust diagnostic modality (Endocrine 2014;46:160)
Radiology Description
  • US findings suspicious for cancer: calcification, complex cysts with internal echoes and solid vascularized vegetation (Endocrine 2014;46:160)
  • CT findings suggestive of malignancy include the presence of a solid component, dense or enhancing mural nodules, calcification, an irregular margin or a thickened cyst wall (AJNR Am J Neuroradiol 2000;21:1547)
Radiology Images

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Neck ultrasound

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Multicystic lesion

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Calcification

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Infrahyoid lesion

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Low density


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Axial and transverse

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Cystic swelling

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Thick septae

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Solid component

Prognostic Factors
  • Excellent prognosis, similar to that of the usual papillary carcinoma of thyroid gland
  • Histotype is one of the prognostic factors, with squamous cell carcinoma being the most aggressive tumor
Case Reports
Treatment
  • Most TGD carcinomas are managed initially by the Sistrunk procedure
  • Further steps may include:
    • Total thyroidectomy
    • Neck dissection
    • Radioiodine ablation
  • Currently, there are no specific guidelines on optimal management of TGD cyst cancer, and controversy mostly centers on the role of thyroidectomy (J Clin Endocrinol Metab 2013;98:458, Laryngoscope 2016;126:1709)
  • Squamous cell carcinoma of TGD seems to be more aggressive than papillary cancer and may warrant more extensive surgery and even postoperative irradiation
Clinical Images

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Neck mass


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Intraoperative

Gross Description
Gross Images

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Thyroidectomy

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Total resection

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Thyroglossal duct

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Thyroglossal cyst


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Modified neck dissection

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Sistrunk procedure

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PTC in TGD cyst

Micro Description
  • Typical thyroid carcinoma (nuclear features and microarchitecture compartible with specific histotype) in the context of a TGD cyst with epithelial lining
  • Invasion of the hyoid bone and adjacent soft tissue is common
Micro Images
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Contributed by Andrey Bychkov, M.D., Ph.D.

Cystic papillary carcinoma

Papillary structures
with apparent
vesicular nuclei



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Papillary carcinoma

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TGDC wall


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Papillary pattern

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Overcrowding nuclei

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Columnar epithelium

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Cystic neoplasm

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Squamous epithelium


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Papillary appearance

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Irregular nucleus

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Microcalcifications

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Papillary carcinoma

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Normal cyst wall lining


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PTC tall cell variant

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Squamous cell carcinoma


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Mucoepidermoid tumor

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TTF1, thyroglobulin

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Thyroglobulin

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CK19

Virtual Slides

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Case 6

Cytology Description
  • FNA findings range from a nonspecific cystic lesion to features characteristic of papillary or squamous cell carcinoma (Am J Clin Pathol 1996;106:615)
  • To increase FNA yield:
    • Ultrasound guided biopsy of the solid portion of cystic mass
    • Liquid based cytology (LBC) of evacuated cystic fluid (Virchows Arch 2014;465:67)
    • Sampling of residual mass after fluid evacuation
Cytology Images

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Papillary carcinoma in TGD cyst aspirate

Positive Stains
Molecular / Cytogenetics Description
Differential Diagnosis
  • Distinguishing TGD associated carcinoma from either primary pyramidal thyroid lobe cancer or Delphian node metastasis is critically important for staging and treatment (Endocr Pathol 2015;26:75, Laryngoscope 2016;126:1709)
    • Primary cancer of the pyramidal lobe:
      • Papillary carcinoma surrounded by a background of benign thyroid parenchyma
      • Absence of TGD epithelium (respiratory / squamous) and lymph node structures
    • Nodal metastasis:
      • Lymph node architecture, including lymphoid stroma and subcapsular sinus
      • Lack of TGD epithelium (respiratory / squamous) and thyroid parenchyma
      • Occult / evident cancer in thyroidectomy specimen