Head and Neck Pathology Case Studies


CASE 6: Thyroglossal Duct Cyst


Clinical History:

A 12-year-old child has complained of a "bump" on his neck for the past month. Physical examination reveals a nontender mass about 2 cm in size in the midline of the neck beneath the skin above the thyroid cartilage. A head and neck CT scan is performed. The mass is excised and examined in surgical pathology.

Gross and Microscopic Pathology:

The CT scan reveals a cystic mass filled with fluid. The wall of the cyst is thin and rounded, with a sharp margin. Grossly, the mass is circumscribed. Microscopically, at the left the cyst cavity can be seen to be lined by pseudostratified ciliated respiratory epithelium. Beneath the epithelium is connective tissue with a few lymphocytes. Lateral to this at the right can be seen thyroid follicles.

Questions:

  1. What is the diagnosis?

    2. This is a thyroglossal duct cyst.

  2. Explain how this lesion occurs.

    3. The lesion is the result of an embryologic remnant. The primordial tissue destined to be thyroid begins its journey at the foramen cecum of the tongue and descends anteriorly in the neck to finally take up residence next to the thyroid cartilage. If remnants of this tissue remain along the track of descent (thyroglossal duct) then they can give rise to a cystic mass. The cyst can be lined by squamous or respiratory epithelium, with or without adjacent thyroid tissue. If not all of the tissue is removed (made more difficult if the track involves hyoid bone) then recurrence of a cystic mass is possible. The lesion is benign.

  3. What is the differential diagnosis of this lesion?

    4. A cystic mass that appears in the lateral neck is a branchial cleft cyst, which is lined by squamous epithelium and has prominent associated lymphoid tissue. Branchial cleft cysts are remnants from embryologic 3rd and 4th pharyngeal pouches.

    A thyroid mass lesion (asymmetric nodular goiter or thyroid neoplasm) would appear lower in the neck than the thyroglossal duct cyst.

    Lymphadenopathy, from infection or metastasis, would typically appear higher and lateral in the neck (cervical nodes).