Embyrology And Congenital Malformations

Question 1

From which germ layer does the nervous system develop from?

Answer 1

Ectoderm

Question 2

What forms the neural tube?

Answer 2

Thickening of ectoderm anterior to the primitive streak called the neural plate
The neural plate thickens and folds (neural folds) to form the neural tube

Question 3

What are 3 neural tube defects and what are they caused by?

Answer 3

Caused by failure of the neural tube to close properly

• anencephaly
• encephalocoele
• Spina Bifida

Question 4

What is encephalocoele?

Answer 4

Failure in closure of the anterior neural tube

Results in herniation of cerebral tissue through a defect in the skull

Question 5

What is Spina Bifida?

Answer 5

Defective closure of the caudal end of neural tube

Non fusion of vertebral arches

Question 6

What is the main difference in the pathology of Spina Bifida cystica with meningocele and meningomyelocle and myeloschisis?

Answer 6

Meningocele - protrusion of meninges and CSF
Meningomyelocle - protrusion of nerve roots and/or spinal cord
Myeloschisis - open spinal cord

Question 7

What are risk factors for Spina Bifida?

Answer 7

Genetic predisposition
Nutritional i.e. folic acid, too much vitamin A
Environmental i.e. hyperthermia (high fever) Na valproate

Question 8

What has a huge impact on decreasing the incidence in neural tube defects?

Answer 8

Folic acid supplements in pregnancy

Question 9

How are neural tube defects detected in pregnancy?

Answer 9

Prenatal screening;

• maternal blood screening (AFP in serum)
• amniocentesis (AFP in amniotic fluid)
• USS

Question 10

When can anencephaly be detected in pregnancy?

Answer 10

12 weeks

Question 11

When can Spina Bifida be detected in pregnancy?

Answer 11

Weeks 16-20

Question 12

What are the 3 primary brain vesicles?

Answer 12

Prosencephalon - forebrain
Mesencephalon - midbrain
Rhombencephalon - hindbrain

Question 13

What are the 3 flexures of the developing brain and where do they occur?

Answer 13

Cephalon flexure - between midbrain and hindbrain (mesencephalon and rhombencephalon)
Cervical flexure - between hindbrain (rhombencephalon) and spinal cord
Pontine flexure - in hindbrain (rhombencephalon

Question 14

What structures does the diencephalon give rise to?

Answer 14

Thalamus
Hypothalamus
Pituitary gland
Pineal gland

Question 15

What structures does the telencephalon give rise to?

Answer 15

Cerebral hemispheres
Hippocampus
Basal ganglia

Question 16

From what vesicle does the cerebellum and pons develop from?

Answer 16

Metencephalon

Hindbrain - rhombencephalon

Question 17

From which vesicle does the medulla develop from?

Answer 17

Myelencephalon

Hindbrain - rhombencephalon

Question 18

From which embryonic vesicle does the lateral ventricles develop from?

Answer 18

Telencephalon

Question 19

From which embryonic vesicle does the 3rd ventricle develop from?

Answer 19

Telencephalon & diencephalon

Question 20

From which embryonic vesicle does the cerebral aqueduct develop from?

Answer 20

Mesencephalon

Question 21

From which embryonic structure does the 4th ventricle develops from?

Answer 21

Metencephalon & myelencephalon

Question 22

What is hydrocephalus?

Answer 22

Accumulation of CSF resulting in an enlarged brain and cranium

Question 23

What is hydrocephalus frequently due to?

Answer 23

Blocked cerebral aqueduct so the CSF cannot drain properly

Question 24

What are the causes of hydrocephalus?

Answer 24

Genetic
Prenatal viral infections
Prenatal intraventricular haemorrhage
Spina Bifida cystica

Question 25

What type of epithelium is the neuroepithlium?

Answer 25

Pseudostratified

Question 26

Neuoepithelium produces most cells of the CNS except what cells?

Answer 26

Microglia

These are mesenchymal cells that migrate into the CNS

Question 27

What type of cells form the PNS neurones and glia ?

Answer 27

Neural crest cells

Question 28

What is the importance of cortical folding?

Answer 28

Saves space to minimise brain volume

Brings together brain regions that would otherwise be far apart so optimises brain wiring to functional organisation

Question 29

What is lissencephaly ?

Answer 29

Smooth brain
Caused by defective neuronal migration
Results in severe mental impairement, failure to thrive, seizures and abnormal muscle tone

Question 30

What is polymicrogyria?

Answer 30

Excessive number of small gyri

Neurological problems - mental retardation, seizures, motor deficits

Question 31

What is the mild form of Spina Bifida?

Answer 31

Spina Bifida occulta

Question 32

What vertebrae does Spina Bifida occulta occur in 10% of otherwise healthy people?

Answer 32

L5 and L6