18 Pharyngeal Arches Flashcards
An infant was born with a cleft palate. The major portion of the palate develops from which embryonic structure?
The largest part of the palate is formed by the secondary palate, which is embryologically derived from the lateral palatine processes.
The medial palatine process gives rise to the smaller primary palate, located anteriorly.
Name the fontanelles of the skull and which sutures are involved
- posterior fontanelle is located at the junction of the sagittal suture and lambdoid suture
- sphenoidal fontanelle is located at the junction of the squamous suture and the coronal suture
- mastoid fontanelle is located the junction of the squamous suture and the lambdoid suture
- anterior fontanelle is located between the 2 frontal and 2 parietal bones
An infant has a cleft lip. Failure of fusion of which structure is the most likely cause?
The most common cause of cleft lip is failure of fusion of the maxillary process and the intermaxillary segment.
An infant has hypoplasia of the mandible, cleft palate and defects of the eye and ear. Abnormal development of which pharyngeal arch will most likely produce these symptoms?
The first pharyngeal arch would produce these symptoms because the first arch normally gives rise to muscles of mastication, mylohyoid, ant. belly of the digastric, tensor tympani, tensor veli palatini, malleus and incus.
Abnormal dev. of the 2nd arch would affect the muscles of facial expression, the stapes and parts of the hyoid bone.
Abnormal dev of the 3rd arch would affect only the stylopharygeus muscle.
An infant has a lump in his neck. A biospy of the lump shows it is thymic tissue. Based on embryonic origin, which additional structure will have an ectopic location?
Both the inf. parathyroid glands and the thymus are derived from the 3rd pharyngeal pouch. Therefore an ectopic thymus is likely to be associated with ectopic parathyroid tissue.
A patient has congenital hypoparathyroidism, thyroid hypoplasia and no thymus. Abnormal dev. of which pharyngeal pouches or arches will produce these defects?
The defect is likely in the dev. of 3rd and 4th pharyngeal pouches because the superior parathyroid glands are derived from the 4th pouch whereas the inferior parathyroid glands are derived from the 3rd pouch.
The 3rd pouch also gives rise to the thymus and the parafollicular cells of the thyroid gland.
An infant was born without the greater cornuae and the inferior part of the hyoid bone. Failure of dev. of which embryonic structures led to these defects?
The 3rd pharyngeal arch gives rise to the greater cornuae and lower part of the hyoid bone, in addition to the stylopharyngeus muscle.
The 2nd pharyngeal arch gives rise to the lesser cornu and upper part of the hyoid bone.
A patient has a well-defined cystic mass at the angle of the mandible, just anterior to the SCM. What is the diagnosis?
A lateral cervical cyst is caused by remnants of the cervical sinus and would present anterior to the SCM.
A patient has a craniopharyngioma occupying the sella turcica, primarily involving the suprasellar space. What is the cause of the tumor?
During embryologic dev. of the pituitary gland, an outgrowth from the roof of the pharynx (Rathke’s pouch) forms the anterior lobe (pars distalis) of the pituitary gland. Since this gland normally occupies the sella turcica, it is most likely a tumor derived from Rathke’s pouch that is extending up into the sella turcica and the space just above it, the suprasellar space.
An infant has a hypoplasia of the mandible, underdevelopment of facial bones, downward-slanting palpebral fissures, defects of the lower eyelids and deformed external ears. Abnormal dev. of which of the pharyngeal arches would produce these symptoms?
The 1st pharyngeal arch, which is associated with the mandible, is responsible for dev. of Meckel’s cartilage, malleus, incus and mandible.
Which sinus is present at age 1?
The maxillary sinus arises late in fetal dev. and is the only sinus present at birth.
The frontal and sphenoid sinuses often develop at approx. 2 years of age from the ant. ethmoid air cells and the post. ethmoid air cells respectively.
A newborn is diagnosed with Treacher Collins syndrome. Examination reveals down-slanting palpebral fissures, defects of the lower eyelids and deformed external ears. Abnormal dev. of which pharyngeal arch will produce these symptoms?
The 1st pharyngeal arch gives rise to the maxillary and mandibular prominences. Failure or insufficient migration of NCCs here leads to Treacher Collins syndrome.
A patient has a soft fluid-filled mass on the left side of the neck at the level of the laryngeal prominence. A diagnosis of branchial cyst is made. Which embryologic structure is most likely contributing to this mass?
Cervical cysts, sinuses and fistulas may develop from parts of the 2nd pharyngeal groove, the cervical sinus or the 2nd pharyngeal pouch that fail to obliterate.
A patient has a bulging and red tympanic membrane. What is the embryologic origin of the structure that allowed the infection to spread frorm the pharynx to the middle ear cavity?
The 1st pharyngeal pouch gives rise to the tympanic recess, with its membrane giving rise to the tympanic membrane. The tympanic recess itself gives rise to the tympanic cavity and the mastoid antrum. The pharyngotympanic tube (eustachian), a part of the tympanic cavity, connects the tympanic cavity to the pharynx.
