Embryological basis of common congenital anomalies Flashcards
Development of pharyngeal arches/bronchial arches
how many
6 arches but arch 5 involutes – 5 left give rise to major head and neck structures
Each arch has indentation on inside within the adjacent foregut (bronchial pouch) an indentation on the outside of the embryo called the groove
Each arch system supplied by specific cranial nerve , artery and has associated muscles , some give rise to specific tissues such as thyroid and parathyroid. And bony and cartilaginous structures
Ectoderm externally.
Endoderm internally.
A core of mesoderm
1st arch what muscles
muscles of mastication
2nd arch what muscles
muscles of facial expression
3rd arch what muscles
Stylopharyngeus
4th arch m
Constrictors of pharynx, cricothyroid, levator veli palatini
6th arch m
Intrinsic muscles of larynx
1st arch CN
Mandibular division of trigeminal (Vc) supplies
muscles of mastication & mucosa of oral cavity
2nd arch CN
Facial nerve (VII) muscles of facial expression and mucosa of oropharynx (parasympathetic)
3rd arch CN
Glossopharyngeal nerve (IX) Stylopharyngeus muscle and mucosa of pharynx
4th arch CN
Superior laryngeal branch of vagus nerve (X)
Muscles of pharynx and some mucosa of the larynx
6th arch CN
Recurrent laryngeal branch of vagus nerve (X)
Muscles of and some mucosa of larynx
1st branchial cleft forms
external auditory canal
1st branchial pouch froms
middel ear cavity and Eustachian tube - these joint at eh tympanic membrane with external auditory cancel
if the pinna looks odd what happens
1st brachial cleft
Pain sensation from the ear is mediated by cranial nerves V, VI, IX and X (NOT VIII)
If no cause for pain is evident within the ear, think of ‘all the Ts’ (Teeth, TMJs, and Tumours of the Throat, Tonsils, and Tongue.
Failure of involution of the branchial pouches and lateral cervical sinus may lead to several anomalies:
to cysts( ceal both inner and out) m sinus tracts ( blind ending channel) , fistulae ( channels connecting skin to the upper aero digestive tract)
recurrent infections
1st arch problems occur
1st arch anomalies occur
Around the outer ear
In the parotid gland
2nd arch problems occurs where
Cysts occur at Level 2, anterior to sternocleidomastoid (SCM).
Sinus tracts and fistulae may extend from the tonsillar fossa (2nd pouch derivative), between the carotid bifurcation to the skin of the anterior neck
The commonest congenital anomaly from branchial derivative
Tonsillar cancer can look at this need to be sent to ENT doctors 30-40 – HPV oropharyngeal cancer
3rd arch problems
cysts occur at Level 3, deep to SCM.
Sinus tracts and fistulae may extend from the inferior aspect of the tonsillar fossa around the back of the carotid sheath, to the skin of the anterior neck
4th arch problems
Sinus tracts may extend from the apex of the piriform fossa (4th pouch) to the thyroid gland, which may result in recurrent thyroid infections
tongue from what arches
Tongue forms form the 1st and 3rd arches – pain and touch sensation to mucosa of tongue that’s why anterior supplied by trig entail and posterior is from the glosso
Tongue musculature is derived from occipital somites
what nerve
hypoglossal - motor supply
Thyroid gland below Adam’s apple
Thyroid gland then descend to normal psotuon below Adam’s apple
Forms a thyroglosaal duct – this can fail to seal up which could from cysts - swelling within 2cm of the midline – surgeons have to remove and have to remove middle third of hyoid bone too. Called sistrunk procedure
Thyroid gland forms from the floor of the pharynx between the tuberculum impar and copula marked by the foramen caecum, at the junction of the middle and posterior thirds of the tongue
It descends to its normal position below the laryngeal exoskeleton
The tract formed as it descends (thyroglossal duct tract) normally involutes
The tract wraps behind the hyoid bone as the hyoid forms
if the thyroid gland was int eh wrong place how would you test it
Thyroid takes up the iodine to make thyroxine therefore would confirm diagnosis
The special sensory organs (eyes, ears and nose) form from special areas of ectoderm called
placodes - The nasal placode sinks inwards to form a nasal pit, and develops neural attachments to the brain
Skin tissue may become trapped along the path of the nasal pit forming nasal dermoids.
Brain tissue may become trapped along the path of the nasal pit forming Encephalocoeles.
As the nasal placode sinks, it divides the frontonasal process into medial and lateral nasal processes.
The medial processes fuse to form the bridge and septum of the nose.
The ectoderm in the floor of the nasolacrimal groove form the nasolacrimal duct and lacrimal sac.
The maxillary swellings form the checks and maxillae.
Failure of fusion of the facial processes may result in facial cleft, cleft lip and cleft palate.
failure of fusion of the maxillary prominence and medial nasal processes (formation of the primary palate)
forms what
cleft lip
what sinus forms first
The paranasal sinuses form as initial invaginations in the facial skeleton in a process called primary pneumatisation
The sinus then expands in a process called secondary pneumatisation
The maxillary sinuses form first – they are small at birth but enlarge during childhood
Functional endoscopic sinus surgery (FESS)
- if needs to be improved
Sometimes sinuses may fail to form – most commonly the frontal and sphenoid sinuses
what is this called
arrested pneumatization
The bony structures of the head and neck are derived from 3 origins:
Viscerocranium- branchial arch derived
Chondrocranium – cartilage derived – forms skull base
Membranous bones – form skull vault
he skull base (chondrocranium) forms from:
3 sets of cartilages close to the midline
Prechordal cartilage – forms ethmoids
Hypophyseal cartilage – forms body of sphenoid
Parachordal cartilage – forms clivus
Cartilaginous capsules forming around the sensory organs
Sphenoid wings forming part of orbit
Temporal bone housing inner ear
chrondorsarcoma
The otic placode forms on the outer surface of the embryo and sinks into the developing temporal bone to form the otic pit
The otic pit ‘pinches off’ via a process of programmed cell death (apoptosis) to form an otic ves
The otic vesicle undergoes a complex sequence of remodelling events to form the definitive sensory structures of the inner ear
Cochlea – hearing
Vestibule – linear acceleration
Semi-circular canals - rotation
Interruption of this remodelling process leads to inner ear abnormalities
This will present as congenital sensorineural hearing loss
Severe sensorineural hearing loss can be treated with a
cochlear implant - directly stimulates cochlear nerve cells
