Embryology of the Pharyngeal Apparatus, Face, and Neck

Vocabulary flashcards covering the embryological development, anatomical derivatives, and congenital malformations of the pharyngeal apparatus, face, tongue, thyroid, salivary glands, and palate.

Stomodeum

The primitive mouth appearing as a shallow depression in the surface ectoderm, separated from the primitive pharyngeal cavity by the bilaminar oropharyngeal membrane.

Meckel's cartilage

The cartilaginous bar of the first pharyngeal arch whose dorsal end forms the malleus and incus of the middle ear, and whose perichondrium forms the anterior ligament of the malleus and sphenomandibular ligament.

Reichert's cartilage

The cartilage of the second pharyngeal arch that gives rise to the stapes, styloid process of the temporal bone, stylohyoid ligament, and lesser horn of the hyoid bone.

Cervical sinus

A temporary ectodermal depression formed during the fifth week when the second pharyngeal arch enlarges and overgrows the third and fourth pharyngeal arches.

Tubotympanic recess

An elongation of the first pharyngeal pouch that gives rise to the tympanic cavity, mastoid antrum, and pharyngotympanic (auditory) tube.

Tonsillar sinus

A depression between the palatoglossal and palatopharyngeal arches derived from the remaining cavity of the second pharyngeal pouch, where the palatine tonsil develops.

Inferior parathyroid glands

Endocrine glands that develop from the dorsal bulbar portions of the third pair of pharyngeal pouches and descend with the thymus to a position inferior to those from the fourth pouches.

Superior parathyroid glands

Endocrine glands that develop from the dorsal bulbar portions of the fourth pair of pharyngeal pouches and attach to the dorsal surface of the thyroid gland.

Ultimobranchial body

An endodermal structure derived from the elongated ventral portion of the fourth pharyngeal pouch that fuses with the thyroid gland to give rise to calcitonin-producing parafollicular (C) cells.

Cervical fistula

An abnormal passage opening internally into the tonsillar sinus and externally on the lateral aspect of the neck, caused by the persistence of parts of the second pharyngeal cleft and second pharyngeal pouch.

Cervical cyst

A spherical or elongated fluid-filled swelling located below the angle of the mandible or along the anterior border of the sternocleidomastoid muscle, derived from remnants of the cervical sinus or second pharyngeal cleft.

Branchial vestige

A rare subcutaneous remnant of cartilage or bone derived from the pharyngeal arch cartilages, typically located anterior to the lower third of the sternocleidomastoid muscle.

Treacher Collins syndrome

An autosomal dominant disorder within first arch syndrome caused by mutations in the TCOF1 gene, characterized by malar hypoplasia, downward-slanting palpebral fissures, lower eyelid defects, and ear deformities.

Pierre Robin sequence

A condition within first arch syndrome characterized by primary micrognathia, which causes posterior displacement of the tongue and prevents closure of the palatal shelves, resulting in a bilateral cleft palate.

DiGeorge syndrome

A disorder caused by 22q11.2 microdeletion leading to failure of the third and fourth pharyngeal pouches to differentiate, resulting in congenital absence of the thymus and parathyroid glands, cardiac outflow tract defects, and facial dysmorphism.

Lingual thyroid gland

The most common type of ectopic thyroid tissue, occurring when the thyroid fails to descend and remains as intralingual masses near the foramen cecum.

Pyramidal lobe

A thyroid lobe present in approximately 50% of individuals that extends rostrally from the isthmus, representing a remnant of the inferior end of the thyroglossal duct in which thyroid tissue formed.

Thyroglossal duct cyst

A painless, mobile, progressively enlarging mass formed by persistent remnants of the thyroglossal duct, most commonly located in the anterior neck inferior to the hyoid bone.

Congenital hypothyroidism

The most common metabolic disorder in newborns, caused by mutations in genes such as the TSH receptor or thyroid transcription factors (TTF-1, TTF-2, PAX8), which can lead to neurodevelopmental disorders and infertility if untreated.

Thyroid hemiagenesis

The congenital absence of one thyroid lobe, most frequently affecting the left lobe, potentially involving mutations in the TSH receptor.

Tuberculum impar

A median triangular elevation appearing at the end of the fourth week on the floor of the primitive pharynx anterior to the foramen cecum, marking the first sign of tongue development.

Lateral lingual swellings

Two bilateral distal tongue buds derived from mesenchyme of the first pharyngeal arch that rapidly enlarge and fuse to form the anterior two-thirds (oral part) of the tongue.

Hypobranchial eminence

A mesenchymal swelling from the third and fourth pharyngeal arches that overgrows the copula to form the posterior third (pharyngeal part) of the tongue and the epiglottis.

Filiform papillae

Thread-like lingual papillae that develop during the early fetal period (weeks 10 to 11) containing tactile-sensitive afferent nerve endings.

Ankyloglossia

A condition in which a short lingual frenulum extends to the tip of the tongue, restricting free tongue protrusion, present in approximately 1 in 300 US neonates.

Macroglossia

Excessive enlargement of the tongue resulting from generalized hypertrophy, most commonly due to a lymphangioma or muscular hypertrophy, frequently seen in Down syndrome or Beckwith-Wiedemann syndrome.

Microglossia

A rare anomaly characterized by an excessively small tongue, typically associated with micrognathia and limb defects in Hanhart syndrome.

Glossoschisis

A deep median groove or cleft tongue resulting from incomplete fusion of the lateral lingual swellings.

Parotid glands

The first salivary glands to develop (at the beginning of week 6), originating from ectodermal buds near the angles of the stomodeum, with secretory activity beginning at 18 weeks.

Submandibular glands

Salivary glands appearing at the end of the sixth week from endodermal buds in the floor of the stomodeum, forming acini at 12 weeks and beginning secretion at 16 weeks.

Sublingual glands

Endodermal salivary glands appearing during the eighth week from multiple epithelial buds that form 10 to 12 independent ducts opening into the floor of the mouth.

Nasolacrimal duct

A duct developing from a solid ectodermal rod in the floor of the nasolacrimal groove that canalizes by apoptosis and drains into the inferior meatus after birth.

Nasolacrimal duct atresia

A congenital lack of opening in part of the nasolacrimal duct causing obstruction symptoms observed in approximately 6% of newborns.

Auricular hillocks

Six mesenchyme nodular masses derived from the first and second pharyngeal arches that fuse around the first pharyngeal cleft to form the auricle of the external ear.

Vomeronasal organ

A chemosensory tubular bilateral structure located in the nasal septum cranial to the paraseptal cartilage, reaching peak development between weeks 12 and 14.

Primary palate

A wedge-shaped mesenchymal mass formed by the fusion of medial nasal prominences (intermaxillary segment) during the sixth week, forming the premaxillary part of the maxilla anterior to the incisive foramen.

Secondary palate

The primordium of most of the hard palate and all of the soft palate, formed by the fusion of two lateral palatine processes extending from the maxillary processes between weeks 7 and 12.

Cleft lip

A congenital facial anomaly occurring with or without cleft palate in approximately 1 in 1,000 births (60–80% male), caused by failure of mesenchymal fusion between the maxillary process and medial nasal prominence.

Cleft palate

A congenital malformation occurring in approximately 1 in 2,500 births (more frequent in females), caused by failure of the lateral palatine processes to fuse with each other, the nasal septum, or the primary palate.

Simonart's band

A band of tissue bridging the two sides of an incomplete unilateral cleft lip.

Microstomia

A congenital condition characterized by an excessively small mouth resulting from excessive fusion of the mesenchymal masses of the maxillary and mandibular processes of the first arch.

Oblique facial cleft

A rare facial cleft extending from the upper lip to the medial margin of the orbit, resulting from failure of the maxillary processes to fuse with the lateral and medial nasal prominences.

Macrostomia

An abnormally large mouth resulting from bilateral lateral or transverse facial clefts extending from the mouth toward the auricles.