A 17-year-old male is examined by a physician, who notes a mass at the back of the young man's tongue. The physician biopsies the mass, and the pathology repo comes back with a diagnosis of normal thyroid tissue. The occasional presence of such tissue at the back of the tongue is related to the embryonic origin of the thyroid near which of the following structures?
The thyroid gland originates as a mass of endodermal tissue near the foramen cecum, which is near the tuberculum impar (which becomes the central pa of the tongue). During development, the thyroid descends in front of the pharynx, maintaining a connection to the tongue the thyroglossal duct. Usually, the thyroglossal duct disappears. Uncommonly, residual ectopic thyroid tissue can be left anywhere along the path, including at the back of the tongue. (In rare patients, all of the thyroid tissue remains at this site, forming a mass that should not be excised, for obvious reasons!). The first pharyngeal pouch develops into the middle ear and eustachian tube. The nasolacrimal ducts connect the eyes to the mouth. The second pharyngeal arch develops into many muscles of the face and styloid process of the temporal bone.
First pharyngeal pouch
Foramen cecum
Nasolacrimal duct
Second pharyngeal arch