Imaging description

A four-year-old girl presented with a tender midline neck mass. Sonogram of the neck demonstrated a normal thyroid gland anterior to the trachea (Fig. 68.1a). Sonographic images obtained cranial to the thyroid gland at the level of the hyoid bone demonstrated a predominately hypoechoic mass associated with septations and small anechoic components (Fig. 68.1b, c). The mass demonstrated posterior acoustic enhancement most consistent with a cystic lesion as opposed to a solid nodule. The most likely diagnosis for a cystic midline neck mass in a child is a thyroglossal duct cyst (TGDC). The septations within the mass suggest associated inflammation and/or infection. Findings in this case are most consistent with a TGDC complicated by an inflammatory process.

Importance

TGDCs are the most common cause of a congenital neck cyst in a child and are typically located in the midline either at the level of the hyoid bone or in an infra-hyoid location. The thyroglossal duct defines the normal migration path of the developing thyroid gland in the fetus from the base of the tongue caudally to the thyroid’s normal position anterior to the trachea in the lower neck. The thyroglossal duct normally involutes, leaving a remnant in the tongue known as the foramen cecum. If some or all of the thyroid tissue fails to descend in normal fashion, ectopic thyroid tissue will be located in the arrested position. TGDCs result from failure of normal ablation of the thyroglossal duct during thyroid development and occur along the course of the duct from the foramen cecum to the thyroid bed. The majority of TGDCs are located at or near the midline of the neck. On sonography TGDC are usually cystic but they may contain solid components or appear complex with septations. In children TGDCs can range in echogenicity from hypoechoic to heterogeneous. The presence of a thick wall and internal septations correlates with the presence of inflammation. Inflammation may result in increased echogenicity, mimicking a solid lesion. The presence of septations and posterior acoustic enhancement on ultrasound characterizes the lesion as a cystic mass as opposed to a solid nodule and confirms the most likely diagnosis as a TGDC. Treatment consists of complete resection of the cyst and duct up to the level of the foramen cecum and is usually curative.