Develop,ent Of Head And Neck And Clinical Relevance 1

Question 1

What are the pharyngeal apparatus components?

Answer 1

PHARYNGEAL ARCHES
Develop from mesoderm and migrating neural crest cells

PHARYNGEAL GROOVES/CLEFTS
Separate the arches externally Lined by ectoderm

PHARYNGEAL POUCHES
Separate the arches internally Lined by endoderm

PHARYNGEAL MEMBRANES
Areas between arches where the ectoderm and endoderm meet.

Question 2

Summarize tissue organ development

Answer 2

Neural crest cells
Migrate to the pharyngeal arches

Pharyngeal arches
Gives rise to skeleton, connective tissues, nerves etc

Occipital myotomes
Migrates to pharyngeal arches

Question 3

Describe the Cranio-facial development

Answer 3

Skull develops from mesenchyme surrounding the developing brain

Neural crest cells migrate from the neural
tube to the craniofacial region to form the mesenchyme of the facial prominences

Because the facial prominences are influenced by brain development, alterations in brain morphology will affect the developing face and overlying structures

Neural crest cells are generally responsible for the induction of the skeletal elements of the face

Question 4

What causes neural tube defects?

Answer 4

Neural tube – gives rise to brain & spinal cord

NTD – critical period 3 – 16 weeks [by 16th week most of the neuronal development is completed]

Most common – cranial / caudal neuropores fail to close [Common anomaly in still-born fetuses]

Question 5

What is meroencephaly/anencephaly ?

Answer 5

1 in 1000 births, common in females

• Cranial neuropore fails to fuse in week 4
• Skull is not formed
• Brain tissue (if present) is disorganized and exposed to the amniotic fluid which causes necrosis / degeneration
• Rudimentary brain stem is usually present •Elevated alpha fetoprotein; polyhydramnios

Question 6

What is holoprosencephaly?

Answer 6

• No cleavage of the prosencephalon
• Small undivided forebrain and a large single fused ventricle
• Can cause craniofacial anomalies ranging from mild to severe .Usually there are midline structural abnormalities due to a smaller frontonasal prominence i.e. there might be a single eye, nasal cavity and single incisor teeth
• 1:16,000 live births
• Due to environmental and genetic factors (Sonic Hedgehog)
• Severe NTD Most infants usually die within 6 months

Question 7

What is Microcephaly?

Answer 7

• Abnormally small calvaria and brain but normal sized face
• Reduction in brain growth

• Underdeveloped brain leads to
severe neurological defects

• Genetic and environmental factors – Viruses
– Ionizing radiation
– Drugs: Fetal Alcohol Syndrome

Question 8

What does the skull develop from?

Answer 8

The skull develops from the mesenchyme around the developing brain
• Neurocranium – forms the bones of the cranial base and cranial vault
• Viscerocranium – forms the bones of the face
• Each has cartilaginous and membranous parts
• Bony skull formed by two mechanisms – intramembranous and endochondral ossification

• Ossification is in a sequence beginning with occipital bone, body of sphenoid,
and ethmoid bone

Question 9

What is the membranous Neurocranium Calvaria(cranial vault)?

Answer 9

Intramembranous ossification of the mesenchyme at sides and top of brain
Separated by sutures

Membranes which form the fibrous joints Six fontanelles found where sutures meet

Question 10

What are the different sutures?

Answer 10

Frontal (Metopic suture). This extends from the top of the head down the middle of the forehead, toward the nose. The 2 frontal bone plates meet at the frontal (metopic) suture.

Coronal suture. This extends from ear to ear. Each frontal bone plate meets with a parietal bone plate at the coronal suture.

Sagittal suture. This extends from the front of the head to the back, down the middle of the top of the head. The 2 parietal bone plates meet at the sagittal suture.

Lambdoid suture. This extends across the back of the head. Each parietal bone plate meets the occipital bone plate at the lambdoid suture.

Question 11

What are the 2 main fontanelles?

Answer 11

• Anterior –The junction where the
2 frontal and parietal bones meet. The anterior fontanelle closes at 18-24 months. This fontanelle can be used to assess intracranial pressure due to e.g. intracranial masses . A sunken
fontanelle is generally a sign of dehydration

• Posterior–Thejunctionwherethe 2 parietal bones meet the occipital bone. This fontanelle generally closes before the anterior fontanelle at about 3 months

Question 12

What is a craniosynostosis?

Answer 12

One or more of the fibrous sutures in an infant skull fuses prematurely thereby changing the growth pattern of the skull

Trigonocephaly

Early closure of the frontal (metopic) (fibrous joint that runs from the anterior fontanelle to the tip of the nose.

Physical examination :
• Noticeable ridge extending along center of
forehead
• Forehead appears narrow
• Eyes may be close together
• Front of the skull may be pointed and triangular

Clinical symptoms:
In extreme cases;
▪ Developmental delays
▪ Learning and behavioral problems 
▪ Vision defects

Question 13

What is Scaphocephaly?

Answer 13

▪ Most frequent type of craniosynostosis

▪ Caused by the premature closure of the sagittal suture

▪ Enlargement of the cranium in the anterior/ posterior dimensions. On physical examination
there is a long narrow shaped head with prominent frontal and occipital regions

▪ CT scan shows long narrow shape of the head with bossing of the frontal and occipital
regions

Question 14

What is Brachycephaly?

Answer 14

Craniosynostosis due to the premature closure of the coronal sutures
On physical exam there might be flattening of the frontal and occipital regions

Question 15

What are the clinical features of plagiocephaly?

Answer 15

• Missing, full, or bulging “soft spot” (fontanel) on the newborn’s skull •Bony ridges along the affected sutures
• Facial abnormalities including bulging forehead and brow on one side, uneven cheekbones, eye sockets, or lower jaw
• Prominent blood vessels in the scalp
• Poor feeding or projectile vomiting
• Seizures
• X-rays to check for fused (missing) sutures or ridges along sutures
• Diagnostic imaging, especially CT scans, also to check for fused sutures or ridges along sutures

Question 16

What causes plagiocephaly?

Answer 16

Premature closure of the coronal suture on one side of the skull

Question 17

What is cranium bifidum?

Answer 17

• Defect in the formation of cranial vault usually in the midline
• Often in the occipital bone including foramen magnum but can occur in the frontal and nasal bones
• Leads to encephalocele - herniation of intracranial contents
• Approximately 1 in 2000 births

Question 18

Whaat is special about cranium bifidum with meningocele?

Answer 18

Swelling contains meninges & CSF

Detect at posterior fontanelle of cranium

Question 19

What is cranium bifida with meningoencephalocele?

Answer 19

Swelling contains meninges, CSF & brain

Detect in cranium at Foramen magnum

Question 20

What is cranium bifidum with meningohydroencephalocoele?

Answer 20

Detect at posterior fontanelle of cranium

Swelling contains extensions of meninges, CSF, brain and ventricle

Question 21

What is the Arnold-Chiari Malformation?

Answer 21

• Most common anomaly of the cerebellum (1:1,000)
• Inferior displacement of the vermis of the cerebellum and medulla through the foramen magnum into the vertebral canal
• Posterior cranial fossa is small

• Associated with obstructive (non
communicating )hydrocephalus

• Cranial nerves IX, X and XII may be stretched causing difficulty in speech, swallowing and absent or diminished gag reflex

Question 22

What are the clinical symptoms of the Arnold Chianti malformation?

Answer 22

• Headaches, nausea and vomiting due to raised intracranial pressure
• Muscle weakness in the head and face
• Difficulty swallowing
• Impaired coordination

• In severe cases paralysis

Question 23

Describe imaging of Arnold chairing malformation

Answer 23

Imaging :
• Downward displacement of cerebellar tonsils through
foramen magnum .
• Compression of the brain stem
• Dilation of the ventricular system due to non communicating hydrocephalus

Question 24

Describe obstructive/non-communicating hydrocephalus

Answer 24

– block in CSF flow in ventricular system
– congenital stenosis of apertures between the ventricles or the subarachnoid space – genetic, viral infection etc.
– dilatation of ventricles proximal to obstruction
– pressure from the accumulated CSF enlarges the head, thinning of the bones and cerebral cortex

Question 25

Describe the formation of stomodeum

Answer 25

Formation of the stomodeum
• Cranial - Frontal eminence
• Caudal- Heart prominence
Both above- Fold towards each other

• Lateral -1st pair of pharyngeal arches
Mandibular prominences fuse in the midline to form the caudal limit of the stomodeum

Stomodeum is separated from the developing pharynx by the oropharyngeal membran

Question 26

Summarize facial development

Answer 26

Under influence of forebrain, frontonasal ectodermal zone and developing eye

Five facial primordia develops:
• 1 frontonasal prominence – surrounds the ventrolateral forebrain from which the optic vesicles form

The following two derived from. 1st arch
• 2 maxillary prominences
• 2 mandibular prominences

Bilateral oval thickenings of surface ectoderm develop on the inferolateral parts of the frontonasal prominence
• •
Nasal placodes, convex initially but become stretched to produce a flat depression
Mesenchyme in the margins of the placodes proliferate to produce horseshoe shaped elevations
-Medial nasal prominence
-Lateral nasal prominence

Nasolacrimal groove is infero-lateral to the lateral prominence separating it from the maxillary prominence.

Question 27

What is the significance of the intermaxillary segment?

Answer 27

During the next few weeks the different prominences of the face increase in size and change relative position. Maxillary prominences grow medially compressing the medial nasal prominences to the midline causing them to fuse.

Maxillary prominences increases in size to form the cheeks and maxilla
The nasal pit deepens

The nasolacrimal groove ectoderm forms a solid epithelial cord that detaches from the overlying surface ectoderm and runs from the medial corner of the eye to the lower aspect of the nasal cavity

The mandibular prominences merge across the midline to form the lower lip and jaw

Question 28

Describe development of the palate

Answer 28

Primary palate: Develops from the deep part of intermaxillary segment (median palatine process). Fuses with secondary palate at incisive foramen
Adult: premaxilla and small part of hard palate

Secondary palate: Bone extends from primary palate into palatine processes. Fuses with primary palate at incisive foramen
Adult: majority of hard palate, soft palate

Question 29

Explain development of the secondary palate

Answer 29

Two lateral vertical shelf like outgrowths from the maxillary processes on either side of the tongue (lateral palatine processes)

Development of the lower jaw and increase in size of the processes themselves assist in repositioning the palatine shelves.

The tongue has moved downwards and the palatine shelves(lateral palatine process) are now horizontal

Lateral palatine process (palatal shelves) fuse in the midline at the same time as the nasal septum grows down.

They fuse to the primary palate anteriorly and the junction is demarcated by the incisive foramen.

The fusion takes places an antero-posterior direction.