Papillary Thyroid Carcinoma within a Thyroglossal Cyst: A Rare Case Report with Review of Literature

Abstract

Thyroglossal cyst (TGC) is the most common congenital anomaly of the thyroid gland and is found in approximately 7% of general population. It represents cystic degeneration of a remnant of the thyroglossal duct that failed to involute during gestation. Malignancy occurring in TGC is rare entity, accounting only for 1% of all thyroglossal cysts. We are presenting such a rare case of papillary thyroid carcinoma arising in a thyroglossal cyst. 30-year-old female presented with a painless, gradually progressive swelling below the chin extending to left side. On examination, swelling was noted in submental region and measuring 4 × 3 × 1 cm, firm in consistency and moves with deglutition and movement of tongue. On radiological investigations, lobulated cystic lesion in midline with thin septations was seen, suggestive of thyroglossal cyst. The thyroid of the patient was normal. Patient underwent Sistrunk procedure. On histopathology, papillary thyroid carcinoma in thyroglossal cyst was seen and it was invading cyst wall and superficial skeletal muscle. The 1st case of thyroglossal duct carcinoma was reported by Brentano in 1911. Till now 300 cases have been reported in literature. Carcinomas occurring in thyroglossal cyst are extremely rare, (< 1% cases). The most frequent histological type is papillary pattern followed by mixed(papillary and follicular), squamous cell, Hürthle cell, follicular and anaplastic variety. The etiology of thyroglossal duct carcinoma is unknown and neither good clinical history nor examination can lead to a preoperative diagnosis. Diagnosis is often incidental on histopathology as in present case. Thyroglossal duct carcinoma is a rare condition that comes as a surprise to both the patient and surgeon and should be considered in patients presenting with cystic midline neck masses. 

Introduction

The thyroid gland arises from a midline endodermal invagination of the foregut, at the level of the foramen caecum during 3rd week of fetal life [1]. During development, an epithelial tract is left behind beneath the thyroid cartilage; it disappears during 8th to 10th week of gestation [2, 3]. Failure of obliteration of the thyroglossal duct during embryonic development can lead to formation of thyroglossal duct cysts (TGDCs) [3, 4]. Brentano described the first carcinoma case in thyroglossal duct cyst in 1911 [5].

During childhood, about 70% of midline masses in the neck and in adults 7% of midline masses in the neck are TGDCs [6]. Reported cases of malignancy in thyroglossal cyst are extremely.

rare(1–2%) [7, 8]. Papillary carcinoma is the most common primary thyroglossal duct cyst carcinoma (75−80%) followed by mixed papillary-follicular carcinomas (7%), squamous cell carcinoma (5%), follicular carcinoma (1.7%), Hürthle cell carcinoma and anaplastic carcinoma (0.9%) [1, 7]. TGDC carcinoma is common in the third and fourth decades of life and rare in children and adolescents [9]. Till now in literature ,there have been 300 reported cases of malignancy associated with TGDCs [10].

We present a rare case of papillary thyroid carcinoma arising within a thyroglossal duct cyst along with a review of the current literature.

Case Report

30-year-old female presented with a painless, gradually progressive swelling below the chin extending to left side. Thyroid function test was normal and patient had no other complaints. There was no history of radiation to head or neck region. Her personal and past medical history is noncontributory. On examination, firm swelling of 4 × 3 × 1 cm was noted in submental region extending to left side which moved with deglutition and protrusion of tongue. There was no cervical lymphadenopathy and no palpable abnormalities in thyroid. The clinical diagnosis was necrotic lymph node or thyroglossal cyst.

Routine hematological investigations were within normal limits Anti-thyroid Antibody (ATA) was  negative. On neck ultrasonography (USG there was 2.9 × 2.2 × 1.3 cm focal lesion with well-defined echogenic walls, single septum, internal echoes with areas of calcification in wall in submental region and was avascular on doppler. CECT of neck revealed lobulated cystic lesion in midline with thin septations within mylohyoid muscle (Fig. 1). The thyroid of the patient was normal.

Fig. 1.

a and b CECT shows a lobulated cystic lesion in midline in submental region within the mylohyoid muscle layer with thin septations

Following this, the patient underwent Sistrunk procedure without thyroidectomy and the specimen was sent to histopathological examination. The post operative course was uneventful and the patient was discharged. The patient was followed up for 12 months and there was no recurrence of thyroid papillary carcinoma.

On gross examination, excised mass was a single globular whitish tissue measuring 4 × 3 × 2 cm along with hyoid bone 2.2 × 1 × 1 cm. On cut surface, it was uninoculated cystic lesion with focal papillary excrescence. (Fig. 2) Microscopic examination revealed cyst wall with ulcerated lining with areas of papillary projection. The individual cells show overlapping and overcrowding at places. Nuclear enlargement with occasional intranuclear grooving and nuclear clearing is seen. Foci of psammomatous calcification seen. (Fig. 3) The tumor was seen infiltrating the underlying fibro-collagenous tissue and superficial skeletal muscle. (Fig. 4) The hyoid bone was free of tumor. On immunohistochemistry, the tumor cells are positive for PAX8 and TTF1. A histopathological impression of papillary carcinoma of thyroid, classical type arising in a thyroglossal cyst was made.

Fig. 2.

a Excised thyroglossal duct cyst with hyoid bone (red arrow) b Cyst wall with papillary excrescences (whitw arrow)

Fig. 3.

a and b thyroglossal cyst showing ulcerated cyst wall lining and characteristic features of thyroid papillary carcinoma (H&E, 10x) c papillae show overlapping and overcrowding of cells intranuclear grooving and nuclear clearing (H&E, 40x)

Fig. 4.

a and b thyroid papillary carcinoma in thyroglossal duct cyst invading of the underlying fibrocollagenous tissue and superficial skeletal muscle (H&E, 40x)

Discussion with Review of Literature

One of the earliest endocrine glands to develop in the human embryo is thyroid gland [10]. From the foramen cecum at the base of the tongue, it descends to the front of the neck in close relation to the hyoid bone via the thyroglossal duct [7]. Usually, this thyroglossal duct obliterates and disappears by the tenth week of gestation [1]. Thyroglossal duct cysts (TGDC) is the most common developmental congenital anomaly reported in thyroid and its incidence is around 7% of the adult population [8]. Carcinomas arising in TGDC are rare and the incidence varies from 0.7 to 1.0% with approximately 300 cases reported in English literature; since its first description by Brentano in 1911 [3, 10, 13, 20]. The average age of presentation is 4th decade of life with women being more prone than men to have a TGDC carcinoma (2.1 :1 male-to-female ratio). The most common histological type of malignancy occurring in TDGC is thyroid papillary carcinoma (80%) followed by squamous, follicular, mixed papillary/follicular, Hürthle cell and anaplastic carcinoma [1, 5, 11].

The etiology of carcinoma in a thyroglossal cyst is unknown and a pre operative diagnosis is difficult with good clinical history and examination [2]. The initial symptoms of thyroglossal duct cyst carcinoma are indistinguishable from a benign thyroglossal duct cyst [1, 5]. A rapid increase in the size of the growth, dysphasia, dysphonia, associated lymphadenopathy and the fixed mass which is not moving freely on deglutition may indicate a malignant change [9, 12]. 

Ultrasonography(USG) is an initial diagnostic modality and the presence of a mural nodule within a cystic lesion, microcalcifications, and the presence of enlarged cervical lymph nodes are findings suggestive of malignancy [8, 11, 12]. Computed tomography (CT) scan and magnetic resonance imaging (MRI) usually show features of solid nodule within the cyst, combined with thickening of the cyst wall, calcification, or intense vascularity within the mass and may help in in pre-operative diagnosis, staging of malignancy, and in planning of primary treatment [1, 9, 11, 13]. Preoperative fine-needle aspiration (FNAC) has an only 53% diagnostic rate for detecting TGDC carcinoma and its role is highly debated [3, 13]. 

Many studies have postulated theories for origin of TGDC carcinoma and the most acceptable theory is that it arises as de novo, as in a majority of cases, ectopic thyroid tissue can be identified histopathologically. Other theories include- (i) multifocal origin in a genetically predisposed individual or a secondary from a papillary carcinoma at thyroid gland.

(ii) metastatic theory which suggests that thyroglossal cyst carcinoma is metastatic from an occult primary in the thyroid gland [3, 5, 6, 8, 13] The diagnosis of primary thyroid carcinoma in TGDC one of exclusion using the Widstrom criteria which include [1]: carcinoma should be in the wall of the thyroglossal duct remnant [2], carcinoma must be differentiated from a cystic lymph node metastasis by histological demonstration of a squamous or columnar epithelium lining and normal thyroid follicles in the wall of the thyroglossal duct remnant, and [3] there should be no malignancy in the thyroid gland or any other possible primary site [2, 7, 14, 15]. 

Thyroglossal duct cyst carcinoma’s definitive treatment is still debatable, raising questions about whether additional management techniques including a total thyroidectomy, regional lymph node dissection, radioactive iodine, and suppressive thyroxine therapy are necessary [2, 7]. Recent studies suggest use of prognostic risk group assessments to identify patients who would benefit from additional total thyroidectomy. Plaza et al. [16]. identified high risk factors: (a) age > 45 years, (b) past radiation exposure, (c) presence of tumor in the thyroid gland on radiological evaluation, (d) presence of clinical/radiological nodes, (e) tumor > 1.5 cm in diameter, (f)cyst-wall invasion, and (g) positive margins on histopathological examination [2, 3, 8, 12, 14]. 

Sistrunk procedure is considered the standard surgical treatment for malignancies with low-risk features and total thyroidectomy with a Sistrunk operation with or without cervical lymphadenectomy with radioiodine and hormone suppressive therapy are considered for patients with high-risk features [8–10, 17, 18].

TGDC carcinoma has an excellent survival rate, at 100% and 95.6% at 5 and 10 years, respectively [3, 9, 19]. Neck nodal metastasis incidence from various studies ranges from 10 to 15%with the risk of metastasis is less than 2% of cases [2, 7, 14]. Careful long-term follow-up is recommended as thyroid papillary carcinoma is usually a low-grade malignancy and recurrences can be successfully treated. It is recommended for all patients to be re-assessed and have a neck scan every six months during the first year and annually after that [2, 6, 20].

Conclusion

Thyroglossal duct cyst (TGDC) carcinoma is a rare and uncommon entity with the majority of cases being diagnosed post-operatively as an incidental finding on histopathological examination. The prognosis of TGDC carcinoma is very good. The management of these patients should be based on their stratification of low and high-risk groups. Due to prolonged natural clinical course of thyroid papillary carcinoma, long term clinical follow up is recommended.

Author Contributions

PSM was responsible for conceiving the idea, literature review and major contributor in writing the manuscript. Dr. SD was responsible for literature review and preparation of histological slides and images. JJ and SB were major contributors for critically revising the manuscript. The authors read and approved the final manuscript.

Funding

This work has no funding resources.

Data Availability

Not Applicable.

Declarations

Conflict of interest

The authors declare that they have no competing interests.

Ethical Approval

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Consent for Publication

Not Applicable.