Teaching Case

An adult male patient presented to ENT OPD with painless swelling in the anterior neck for five months. There were no other complaints. Physical examination revealed a smooth swelling in the infrahyoid neck. There was no significant movement with deglutition. Computed tomography (CT) of the neck was advised.

Pre and post-contrast neck CT (Fig. 1-3) revealed a well-defined cystic lesion in the infrahyoid neck lying anterior to the thyroid cartilage measuring approximately 5.0 cm x 2.6 cm x 3.7 cm. The lesion caused splaying of strap muscles. It contained ill-defined enhancing soft tissue at its inferior aspect (merging with the thyroid isthmus). There was an intensely enhancing thin rim of likely ectopic thyroid tissue along the right lateral margin continuing superiorly to the upper margin of the cyst. No internal calcification was seen nor solid enhancing soft tissue component. The thyroid gland was normal. No suspicious cervical nodes were noted.
CT raised the suspicion of carcinoma in a thyroglossal duct cyst (TDC) and the patient underwent extended total thyroidectomy. Histopathological examination of the specimen showed papillary carcinoma with psammomatous calcification in thyroid tissue within a TDC (Fig. 4).

Thyroglossal duct cysts (TDC) are the commonest congenital cystic neck lesion. They represent epithelial-lined cysts and are typically located in a midline/paramidline location. They occur due to non-obliteration of the thyroglossal duct during development. The most common location is infrahyoid, though they can occur anywhere along the course of thyroglossal duct [1]. The thyroglossal duct arises from the junction of anterior two thirds and posterior one third of the tongue, at the foramen caecum. It courses downwards and passes anterior to the hyoid bone, then curves backwards and descends inferiorly to the isthmus of the thyroid gland.
TDC are usually asymptomatic, unless infected. Malignancy within them is rare (< 1%) [1-3], thyroid papillary carcinoma is the most common histological variant [4]. Most TDC present before 30 years of age, though the average age of development of a carcinoma is 39 years [5]. Malignancy should be suspected in cases where there is a sudden increase in the size of the cyst, pain or associated thyroid invasion on clinical examination.

Imaging modalities like ultrasound, CT and Magnetic Resonance Imaging (MRI) can easily diagnose TDC, however, they may or may not be useful in the preoperative diagnosis of malignancy in a TDC. On ultrasonography, cysts appear anechoic with thin walls. Internal debris may be seen due to secondary infection. CT shows a thin-walled, cystic lesion with or without capsular enhancement. The presence of solid enhancing components raises suspicion for developing malignancy [6], though thickening of the cyst wall and solid components may also be seen in inflammatory processes. The presence of calcification is considered specific although not sensitive for the presence of papillary carcinoma [5]. Fine needle aspiration cytology (FNAC) may reveal positive results in 66% of cases [7]. Preoperative diagnosis is important as it may alter surgical management.

Sistrunk procedure is the surgical treatment of choice for TDC and thyroglossal duct cyst carcinoma in low risk patients (age <45 years, size <4 cm, no prior radiation exposure, no lymphadenopathy/local invasion of the thyroid or distant metastasis) [1, 8]. However, total thyroidectomy with radioactive ablation should be performed in high risk patients [8]. The prognosis for papillary thyroglossal duct cyst carcinoma is excellent, with metastatic lesions seen in less than 2% of cases [1].

Newer modalities like Positron emission tomography (PET) can detect thyroid carcinoma [9] and thus studies are required depicting their role in detecting carcinoma in TDC as well.