Head and Neck Embryology Questions

Unilateral cleft lip is the most common congenital malformation of the head and neck. Cleft
lip occurs when the maxillary prominences fail to fuse with the medial nasal prominences and
when the underlying somitomeric mesoderm and neural crest fail to proliferate, resulting in a
persistent labial groove. Cleft lip occurs in 1 of 900 births and may be unilateral or bilateral.

Taste sensation from the mucosa for the oral part of the tongue is carried by the chorda
tympani branch of the facial nerve (CN VII). This part of the tongue forms from pharyngeal arch
1, so the trigeminal nerve (CN V) will carry sensory innervation from the mucosa

The intermaxillary segment, which plays a critical role in the formation of the definitive adult
palate, forms when the two medial nasal prominences fuse in the midline.

First arch syndrome results from abnormal development of pharyngeal arch 1 due to a lack
of migration of neural crest cells. Treacher Collins syndrome is associated with underdevelopment of the zygomatic bone, down-slanting palpebral fissures, and deformed lower eyelids and
external ears.

The parathyroid and thymus migrate in a caudal and medial direction during development;
therefore, ectopic glandular tissue may be found anywhere along the migratory path.

A pharyngeal fistula forms when pharyngeal pouch 2 and pharyngeal groove 2 persist.
Therefore, these fistulas are found on the lateral aspect of the neck, usually along the anterior
border of the sternocleidomastoid muscle.

The thyroid gland forms from a diverticulum in the midline of the floor of the pharynx.
The thyroid migrates caudally and passes ventral to the hyoid bone. During this migration, the
thyroid remains connected to the tongue by the thyroglossal duct. If a part of the thyroglossal
duct persists, a cyst will develop, usually near the hyoid bone.

The malleus is the only structure on this list derived from the neural crest of the first
pharyngeal arch.