A 7-year-old patient presents with a mass in the anterior midline of the neck, slightly above the larynx. The mass is mobile and elevates upon protrusion of the tongue. This mass is most likely a cyst that developed from which of the following embryonic structures?
a. First pharyngeal cleft
b. First pharyngeal pouch
c. Second pharyngeal cleft
d. Thyroglossal duct
The Correct option is D
Explanation with High Yield Facts:
The thyroglossal duct develops as an evagination of the floor of the pharynx in the region where the tongue develops. The adult foramen cecum of the tongue marks the site of this evagination. The distal end of this duct normally forms the thyroid gland; the proximal part of the duct normally degenerates. Failure of a part of the duct to degenerate may lead to a thyroglossal duct cyst or median cervical cyst, as seen in this patient.
- The first pharyngeal cleft (choice A) forms the external ear canal. This cleft normally remains patent.
- The first pharyngeal pouch (choice B) forms the middle ear cavity and the auditory tube. This pouch normally remains patent.
- The second pharyngeal cleft (choice C) normally does not remain patent. It is typically covered over by the overgrowth of the second pharyngeal arch. If part of this pouch does remain patent, it may form a lateral cervical cyst, which is seen on the lateral side of the neck along the posterior border of the sternocleidomastoid muscle.
- The second pharyngeal pouch forms the tonsillar fossa of the pharynx. The pharyngeal mucosa in this area arises from the endoderm of the pouch. Ingrowths of mesoderm cells results in the formation of the palatine tonsil.
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