Head and Neck Development and Malformations

Question 1

Consists of a dorsal maxillary process which extends forward beneath the region of the eye and a ventral mandibular process which contains Meckel’s cartilage

Meckel’s cartilage is replaced by the mandible which develops by membranous ossification

Maxillary process is replaced by the maxilla which develops by membranous ossification

Meckel’s cartilage disappears except for two small portions at its dorsal end that persist and form the incus and malleus

Contributes to the formation of the bones of the middle ear

Musculature includes muscles of mastication (temporalis, masseter, pterygoids), anterior belly of the digastric, mylohyoid, tensor tempani, tensor palatini

Nerve supply from the mandibular branch of the trigeminal nerve

Mesenchyme also contributes to the dermis of the face, so sensory supply to the skin of the face is provided by the ophthalmic, maxillary, and mandibular branches of the trigeminal nerve

Answer 1

First Pharyngeal Arch

Question 2

Autosomal dominant inheritance with variable penetrance

Caused by a lack of migration of neural crest cells into pharyngeal arch 1

TCOF1 mutation (highly expressed in neural crest cells)

Hypoplasia of zygomatic bones, microtia, colobma/notching of the lower eyelids, hypoplasia of the mandible

Deafness is due to malformation of the ossicles (conductive hearing loss)

Normal intelligence but can be mistaken for mental retardation due to deafness

Answer 2

Mandibulofascial Dystosis (Treacher-Collins Syndrome)

Question 3

Cartilage of the hyoid arch (Reichert’s cartilage) gives rise to the stapes, styloid process of the temporal bone, stylohyoid ligament, and the lesser horn and upper part of the body of the hyoid bone

Stapes, stylohyoid, and lesser hyoid cartilages

Stapedius, stylohyoid, posterior belly of the digastric, auricular, and muscles of facial expression

Facial nerve supplies the muscles

Answer 3

Second Pharyngeal Arch

Question 4

Cartilage of the third pharyngeal arch produces the lower part of the body and greater horn of the hyoid bone

Greater hyoid cartilage

Musculature is limited to the stylopharyngeus muscles

Innervated by the glossopharyngeal nerve

Answer 4

Third Pharyngeal Arch

Question 5

Cartilaginous components fuse to form the thyroid, cricoid arytenoid, corniculate, and cuneiform cartilages of the larynx

Thyroid and laryngeal cartilage
Muscles: cricothyroid, levator palantini, constrictors of the pharynx
innervated by the superior laryngeal branch of the vagus

Intrinsic muscles of the larynx are supplied by the recurrent laryngeal branch of the vagus

Answer 5

Fourth and Sixth Pharyngeal Arches

Question 6

epithelial lining of the auditory tube and middle ear cavity

Answer 6

Adult derivatives of pharyngeal pouch 1

Question 7

epithelial lining of the palantine tonsils crypts

Answer 7

Adult derivatives of pharyngeal pouch 2

Question 8

inferior parathyroid gland and thymus

Answer 8

Adult derivatives of pharyngeal pouch 3

Question 9

superior parathyroid gland, contributes to parafollicular cells of the thyroid

Answer 9

Adult derivatives of pharyngeal pouch 4

Question 10

epithelial lining of the external auditory meatus

Answer 10

Adult derivatives of pharyngeal cleft 1

Question 11

obliterated

Answer 11

developmental fate of pharyngeal clefts 2, 3, and 4

Question 12

Autosomal dominant FGFR2 mutation

Gain of function in dural cells/osteoblasts, specifically in patent suture mesenchyme

Craniofacial abnormalities:
Shallow midface: bulging, wide-set eyes, beaked nose
Hypoplasia of the mandibular, overcrowded teeth

Hearing and vision disturbances

Syndactyly

Sweating and acne

Cognitive abilities range between normal intelligence and intellectual delay

Answer 12

Apert Syndrome

Question 13

Many causes

Classified as anterior or posterior
The incisive foramen separates anterior defects from the posterior defects

Anterior: occurs when the palantine shelves fail to fuse with the primary palate

Posterior: occurs when the palantine shelves fail to fuse with each other and with the nasal septum

Anteroposterior: occurs when there is a combination of both defects

Answer 13

Cleft Palate

Question 14

Occurs when the maxillary prominence fails to fuse with the medial nasal prominence

Underlying somitomeric mesoderm and neural crest fail to expand resulting in a persistent labial groove

May be unilateral (most common) or bilateral

Answer 14

Cleft lip