Embryological basis of common congenital anomalies

Question 1

Development of pharyngeal arches/bronchial arches

how many

Answer 1

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

Question 2

1st arch what muscles

Answer 2

muscles of mastication

Question 3

2nd arch what muscles

Answer 3

muscles of facial expression

Question 4

3rd arch what muscles

Answer 4

Stylopharyngeus

Question 5

4th arch m

Answer 5

Constrictors of pharynx, cricothyroid, levator veli palatini

Question 6

6th arch m

Answer 6

Intrinsic muscles of larynx

Question 7

1st arch CN

Answer 7

Mandibular division of trigeminal (Vc) supplies

muscles of mastication & mucosa of oral cavity

Question 8

2nd arch CN

Answer 8

Facial nerve (VII)
muscles of facial expression and mucosa of oropharynx (parasympathetic)

Question 9

3rd arch CN

Answer 9

Glossopharyngeal nerve (IX)
Stylopharyngeus muscle and mucosa of pharynx

Question 10

4th arch CN

Answer 10

Superior laryngeal branch of vagus nerve (X)

Muscles of pharynx and some mucosa of the larynx

Question 11

6th arch CN

Answer 11

Recurrent laryngeal branch of vagus nerve (X)

Muscles of and some mucosa of larynx

Question 12

1st branchial cleft forms

Answer 12

external auditory canal

Question 13

1st branchial pouch froms

Answer 13

middel ear cavity and Eustachian tube - these joint at eh tympanic membrane with external auditory cancel

Question 14

if the pinna looks odd what happens

Answer 14

1st brachial cleft

Question 15

Pain sensation from the ear is mediated by cranial nerves V, VI, IX and X (NOT VIII)

Answer 15

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.

Question 16

Failure of involution of the branchial pouches and lateral cervical sinus may lead to several anomalies:

Answer 16

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

Question 17

1st arch problems occur

Answer 17

1st arch anomalies occur
Around the outer ear
In the parotid gland

Question 18

2nd arch problems occurs where

Answer 18

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

Question 19

3rd arch problems

Answer 19

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

Question 20

4th arch problems

Answer 20

Sinus tracts may extend from the apex of the piriform fossa (4th pouch) to the thyroid gland, which may result in recurrent thyroid infections

Question 21

tongue from what arches

Answer 21

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

Question 22

Tongue musculature is derived from occipital somites

what nerve

Answer 22

hypoglossal - motor supply

Question 23

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

Answer 23

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

Question 24

if the thyroid gland was int eh wrong place how would you test it

Answer 24

Thyroid takes up the iodine to make thyroxine therefore would confirm diagnosis

Question 25

The special sensory organs (eyes, ears and nose) form from special areas of ectoderm called

Answer 25

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.

Question 26

failure of fusion of the maxillary prominence and medial nasal processes (formation of the primary palate)
forms what

Answer 26

cleft lip

Question 27

what sinus forms first

Answer 27

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

Question 28

Sometimes sinuses may fail to form – most commonly the frontal and sphenoid sinuses

what is this called

Answer 28

arrested pneumatization

Question 29

The bony structures of the head and neck are derived from 3 origins:

Answer 29

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

Question 30

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

Answer 30

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

Question 31

Severe sensorineural hearing loss can be treated with a

Answer 31

cochlear implant - directly stimulates cochlear nerve cells