Imaging of Ectopic Thyroid Tissue and Thyroglossal Duct Cysts

Abstract

When a child or young adult presents with a mass in the anterior portion of the neck, diagnostic considerations include a thyroglossal duct cyst and ectopic thyroid tissue. These entities are often suspected clinically, and imaging provides an opportunity to evaluate the extent, confirm the diagnosis, and evaluate for complications. Imaging characteristics of a thyroglossal duct cyst as a simple cyst and of ectopic thyroid tissue as a hyperattenuating soft-tissue mass can help identify these lesions at computed tomography (CT); however, intrinsic magnetic resonance, CT, and ultrasonographic imaging characteristics alone cannot be used to confirm the diagnosis. Rather, knowledge of the typical course of the thyroid primordium during embryologic development is essential to understand the variant locations along this path where thyroid tissue can be found. The migration of thyroid primordium begins at the foramen cecum at the base of the tongue and then loops around the hyoid bone anteriorly and inferiorly and descends anteriorly to the thyrohyoid membrane into the orthotopic location in the infrahyoid portion of the neck. Thyroid ectopia is categorized into one of four typical locations with respect to this embryologic course: (a) the base of the tongue, (b) adjacent to the hyoid bone, (c) the midline infrahyoid portion of the neck, and, rarely, (d) the lateral part of the neck. The differential diagnosis includes metastatic thyroid carcinoma, branchial cleft cyst, lymphatic malformation, abscess, saccular cyst, epidermoid cyst, and squamous cell carcinoma. The relationship of a mass to landmarks such as the foramen cecum, hyoid bone, strap muscles, thyrohyoid membrane, and thyroid cartilage can help differentiate a thyroglossal duct cyst and ectopic thyroid tissue from other anterior neck masses when the embryologic thyroid course is considered.

Diagnostic imaging of benign and malignant neck masses in children—a pictorial review

“…It is important that the presence and location of thyroidal tissue is determined when thyroglossal duct cyst excision is being planned. This is because the only functioning thyroid tissue may be located within the cyst itself and excision would render the patient hypothyroid (6). There is an association of papillary thyroid cancer affecting This appearance is consistent with a thyroglossal duct sinus.…”

Ultrasonography of Various Thyroid Diseases in Children and Adolescents: A Pictorial Essay

“…Thyroid follicular cells originate as the median thyroid anlage, an endodermal thickening between the first and second pharyngeal arches during the fourth to fifth gestational week. A thickening rapidly forms a small out-pouch referred to as thyroid primordium (5, 6). This structure elongates into a bilobate diverticulum and descends caudally while maintaining contact with the aortic primordium.…”

“…A small channel; i.e., the thyroglossal duct, temporarily manifests as a connection between the tongue and the caudal migration of the thyroid primordium, which then involutes. The thyroid primordium first courses anteriorly to the primordial hyoid bone and laryngeal cartilage, and then loops inferiorly and posteriorly to the hyoid bone before continuing its descent into the infrahyoid portion of the neck (5, 6). By the seventh week, the gland attains its normal final position anterior to the second and third tracheal rings (Fig.…”

Thyroid Ultrasound: State of the Art Part 1 – Thyroid Ultrasound reporting and Diffuse Thyroid Diseases

“…Approximately 80% of congenital hypothyroidism is caused by thyroid dysgenesis due to absence, hypoplasia or ectopia of the gland, which is almost always sporadic in nature [21]. Ectopic thyroid tissue is derived from incomplete migration of thyroid gland and can be found anywhere along the migration course of the thyroid primordium [22] which is between the base of tongue and pretracheal region. The most common presentation is a euthyroid neck mass [23].…”