Discussion
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.
