Enlargement and Transformation of Thyroglossal Duct Cysts in Response to Radiotherapy: Imaging Findings

Abstract

BACKGROUND AND PURPOSE:Thyroglossal duct cyst remnants (TGDC) are a common midline neck mass that is mostly encountered in childhood. Enlargement after an upper respiratory tract infection or, rarely, cancer within TGDC, is a well-documented phenomenon. In the pediatric population, it rarely presents a diagnostic quandary. However, in an adult population, especially one treated for head and neck cancer with radiation therapy (RT), any enlarging cystic mass would be concerning and would raise the specter of metastatic disease. We propose that inflammation associated with RT results in secretory stimulation and/or obstruction of a persistent thyroglossal duct, resulting in changes within a pre-existing TGDC.

Comparison of Prevalence and Ultrasonography Features of Thyroglossal Duct Cyst in Adults According to Radioactive Iodine Ablation

“…In addition, the mean size of TGDCs was 0.9 cm, and there was no significant relationship between size of TGDCs and RIA. In the previous studies [5,7], radiation therapy may be associated with enlargement of TGDCs. The reason for this difference is unclear, but the following factors can be considered.…”

“…On US, TGDCs were defined as thin-walled, anechoic cystic lesions with posterior enhancement in the anterior upper midline neck when it could be differentiated from adjacent muscular or vascular structures. In addition, when the cystic lesion showed atypical content owing to the proteinaceous material or hemorrhage, it was considered as a TGDC [3,5]. The presence or absence, location, largest diameter, and shape of the TGDCs were investigated.…”

“…Thyroglossal duct cyst (TGDC) is the most common congenital abnormality in the neck, accounting for 70–75% of midline neck masses [1–3]. TGDCs are originated from remnants of the thyroglossal duct after the thyroid gland migrates from the foramen cecum to its final site in the anterior lower neck [1–5]. In general, the thyroglossal duct disappears by the 8 th to 10 th week of gestation, but the persistent secretory epithelium may form a cyst when it fails to completely involute [4].…”

“…High-resolution ultrasonography (US) is a useful tool in the diagnosis and management of neuromuscular pathology and abnormalities in the surrounding structures [6]. On US, TGDCs are usually observed as thin-walled, unilocular, anechoic cystic masses with posterior enhancement [5]. Enlargement of TGDCs is a well-documented finding after an infection [1–3].…”

“…Several investigators have reported enlargement of TGDCs after radiation therapy [5,6]. They suggested that repeated inflammation due to radiation therapy may have caused an undetected, subclinical thyroglossal duct to secrete fluid and/or to obstruct the duct, thereby causing it to manifest as a cystic mass [5,7]. However, the relationship between TGDCs and radiation therapy is still unclear.…”