Embryology and Congenital Malformations

Question 1

what does the nervous system develop from?

Answer 1

embryonic ectoderm

Question 2

when does gastrulation start?

Answer 2

week 3

Question 3

when does the CNS appear?

Answer 3

beginning of week 3

Question 4

what is the thickening of ectoderm anterior to the primitive node called?

Answer 4

neural plate

Question 5

the edges of the neural plate thicken and move upwards to for the…

Answer 5

neural folds

Question 6

neural folds migrate towards eachither and fuse at midline forming the…

Answer 6

neural tube

Question 7

when dies tge anterior neuropore close at?

Answer 7

18-20 somite stage, 25 days

Question 8

when does the posterior neuropore close?

Answer 8

day 27

Question 9

with failure of neural tube to close properly results in neural tube defects. Give some examples

Answer 9

Anencephaly
Encephalocoele
Spina bifida

Question 10

what is Exencephaly/Anencephaly(Meroencephaly

Answer 10

Failure of anterior neuropore to close.
Skull fails to form
Brain tissue degenerates.
Incompatible with life.

Question 11

what is Encephalocoele

Answer 11

Herniation of cerebral tissue through a defect in the skull.
Failure in closure of rostral neural tube.
Most frequent in occipital region.
Variable degree of neurological deficits.

Question 12

what is spina bifida?

Answer 12

Defective closure of the caudal neural tube.
Affects tissues overlying the spinal cord.
Spina bifida = non-fusion of vertebral arches.
Neural tissue may or may not be affected.
Severity ranges from minor abnormalities to major clinical symptoms.

Question 13

what can spina bifida occulta result in?

Answer 13

dimple with small tuft of hair

Question 14

what is spina bifida cystica?

Answer 14

Protrusion of spinal cord and/or meninges through the defect in the vertebral arches

Question 15

what is Spina bifida with meningocele

Answer 15

Rarest form

Protrusion of meninges and cerebrospinal fluid

Question 16

what is Spina bifida with meningomyelocle

Answer 16

Nerve roots and/or spinal cord included in the sac
Neurological deficits – loss of sensation and muscle paralysis
Area affected determined by level of lesion
Often associated with hydrocephalus

Question 17

how would you prevent congenital malformations?

Answer 17

Folic acid supplements (400 µg/day  50-70% decrease in risk)

Question 18

what are the prenatal diagnosises?

Answer 18

Maternal blood screening
Indicated by high levels α-fetoprotein (AFP) in serum – AFP from foetal liver leaks into amniotic fluid then into maternal blood.
Best detected 16 - 20 weeks.
- Amniocentisis
(high levels AFP in amniotic fluid)
- Ultrasound
(Anencephaly from 12 weeks, spina bifida from 16-20 weeks)

Question 19

what are some risk factors for congenital malformation

Answer 19

Genetic predisposition
Nutritional (e.g. too little folate, too much vitamin A)
Environmental (e.g. hyperthermia; taking certain drugs – e.g. sodium valproate)

Question 20

when does the Cephalic flexure form? and where does it form?

Answer 20

End of 3rd week.
		Between midbrain (mesencephalon) and hindbrain (rhombencephalon).

Question 21

when does the Cervical flexure form and where?

Answer 21

End of 4th week.

Between hindbrain and spinal cord.

Question 22

when does the pontine flexure form and where?

Answer 22

5th week.
In hindbrain
(between metencephalon and myelencephalon).

Question 23

when does the CSF form?

Answer 23

during 5th week

Question 24

what is Hydrocephalus

Answer 24

Accumulation of cerebral spinal fluid
Results in enlarged brain and cranium
Frequently due to blocked aqueduct

Question 25

what are the causes of Hydrocephalus

Answer 25

genetic, prenatal viral infection or intraventricular haemorrhage, spina bifida cystica

Question 26

what forms the PNS, neurons and ganglia?

Answer 26

Neural crest

Question 27

what causes Lissencephaly ?

Answer 27

Caused by defective neuronal migration.

Question 28

what is Lissencephaly

Answer 28

smooth brain, gyri and sulci fail to develop

Question 29

what does Lissencephaly result in?

Answer 29

severe mental impairment, failure to thrive, seizures, and abnormal muscle tone.

Question 30

what is Polymicrogyria

Answer 30

Excessive number of small gyri.

Question 31

what is the result of Polymicrogyria

Answer 31

mental retardation, seizures, motor deficits etc)

Question 32

what is Porencephaly

Answer 32

CSF filled cysts

or cavities

Question 33

what causes Porencephaly

Answer 33

Usually from postnatal stroke or infection

Question 34

what is the result of Porencephaly

Answer 34

Delayed growth and development, seizures, hypotonia, intellectual impairment

Question 35

what is Aegenesis corpus callosum

Answer 35

there is a complete or partial absence of the corpus callosum

Question 36

what does Aegenesis corpus callosum result in?

Answer 36

Cognitive and social difficulties—-> intellectual impairment, seizures, hypotonia etc

Question 37

what is Schizencephaly

Answer 37

Large clefts or slits

Question 38

what is the cause of Schizencephaly

Answer 38

Genetic, in utero stroke, infection

Question 39

what does Schizencephaly result in?

Answer 39

Paralysis, seizures, intellectual impairment, developmental delay.

Question 40

what is Diastematomyelia

Answer 40

Spinal cord split longitudinally into 2 parts

Question 41

what does Diastematomyelia result in?

Answer 41

Scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation.

Question 42

what are the causes of intellectual impairment?

Answer 42

maternal alcohol abuse.

genetic (e.g. Down’s
syndrome)
Radiation
Infectious agents (e.g. rubella, toxoplasmosis, cytomegalovirus)
Birth trauma
postnatal insults (e.g. head injury, infections (e.g. meningitis), lead exposure