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Thyroglossal duct carcinoma

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Last staff update: 5 September 2023

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Cite this page: Bychkov A. Thyroglossal duct carcinoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/thyroidthyroglossalcarc.html. Accessed April 20th, 2024.

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:
- Contrary to early reports, nodal involvement was found to be high; in series with neck dissections can approach 70% (Endocr J 2013;60:665)
- Some studies found preferred lateral involvement without central compartment involvement (J Clin Endocrinol Metab 2013;98:458)
- Distant metastases are extremely rare (Auris Nasus Larynx 2008;35:11)
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

Multicystic lesion

Calcification

Infrahyoid lesion

Low density

Axial and transverse

Cystic swelling

Thick septae

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

Papillary carcinoma
- 20 year old woman with papillary carcinoma arising in TGD cyst (Acta Otorhinolaryngol Ital 2014;34:215)
- 25 year old woman with papillary carcinoma arising from TGD cyst (Indian J Radiol Imaging 2009;19:120)
- 27 year old man with papillary carcinoma arising in a submental-intralingual TGD cyst (Acta Otorhinolaryngol Ital 2010;30:313)
- 28 year old woman with metastatic TGD cyst papillary carcinoma (Int J Surg Case Rep 2013;4:704)
- 31 year old man with TGD cyst papillary carcinoma (Case Rep Oncol 2011;4:39)
- 35 year old woman with bilateral cervical lymph node metastasis of TGD cancer (Auris Nasus Larynx 2003;30:107)
- 39 year old woman with simultaneous papillary carcinoma in a TGD cyst and the thyroid gland (Case Rep Otolaryngol 2015;2015:382760)
- 44 year old woman with invasive TGD cyst papillary carcinoma (J Med Case Rep 2009;3:9308)
- 64 year old man with papillary carcinoma in TGD cyst (Arch Med Sci 2014;10:1061)
- 77 year old woman with tall cell carcinoma arising in a TGD cyst (Ann Med Surg (Lond) 2015;4:129)
Other cancers
- 38 year old man with concurrent papillary and squamous carcinoma in a TGD cyst (Can J Surg 1996;39:328)
- 48 year old man with papillary and squamous carcinoma in TGD cyst (World J Surg Oncol 2003;1:15)
- 61 year old woman with adenosquamous carcinoma arising in a TGD cyst (Surg Today 2011;41:533)
- 62 year old woman with Hurthle cell carcinoma in TGD cyst (Otolaryngol Head Neck Surg 1995;113:153)
- 68 year old woman with anaplastic carcinoma arising in a TGD tract (Otolaryngol Head Neck Surg 1993;109:945)
- 73 year old woman with mucoepidermoid carcinoma in a TGD remnant (Int J Surg Case Rep 2015;13:43)
- 78 year old woman with coexistence of a carotid body tumor and metastatic TGD carcinoma (Clin Exp Otorhinolaryngol 2014;7:69)
- 84 year old woman with anaplastic carcinoma arising from TGD remnant (Cancer 1981;48:2724)

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

Intraoperative

Gross description

Small mural nodule 1.5 - 2 cm, rarely completely filling the cyst (J Clin Endocrinol Metab 2013;98:458, Laryngoscope 2016;126:1709)

Gross images

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Thyroidectomy

Total resection

Thyroglossal duct

Thyroglossal cyst

Modified neck dissection

Sistrunk procedure

PTC in TGD cyst

Microscopic (histologic) 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

Microscopic (histologic) images

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

Cystic papillary carcinoma

Papillary structures

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Papillary carcinoma

TGDC wall

Papillary pattern

Overcrowding nuclei

Columnar epithelium

Cystic neoplasm

Squamous epithelium

Papillary appearance

Irregular nucleus

Microcalcifications

Papillary carcinoma

Normal cyst wall lining

PTC tall cell variant

Squamous cell carcinoma

Mucoepidermoid tumor

TTF1, thyroglobulin

Thyroglobulin

CK19

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

CK19 and other markers of thyroid carcinoma immunophenotype (Arch Med Sci 2014;10:1061)

Molecular / cytogenetics description

BRAF V600E mutation with a rate comparable to orthotopic papillary thyroid carcinoma (Virchows Arch 2014;465:67)

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

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