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Systems: Neurology AB > Embryology and Congenital Malformations > Flashcards

Embryology and Congenital Malformations Flashcards

1
Q

What does the nervous system develop from?

A

Embryonic ectoderm

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2
Q

When does the CNS begin to appear?

A

Beginning of the 3rd week

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3
Q

Neural plate

A

Thickening of ectoderm anterior to the primitive node

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4
Q

How do the neural folds form?

A

Edges of the neural plate thicken and move upwards to form the neural folds

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5
Q

How is the neural tube formed?

A

Neural folds migrate towards each other and fuse at the midline forming the neural tube

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6
Q

Where does the neural tube initially remain open?

A

Anterior and posterior ends

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7
Q

When does the anterior (cranial/rostral)neurpore close?

A

Closes 18-20 somite stage (~25 days)

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8
Q

When does the posterior (caudal) neuropore close?

A

~day 27

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9
Q

What is essential for normal development and function?

A

Closure of the neural tube

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10
Q

Where is neural tube closure initiated?

A

At several points along A-P axis

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11
Q

What direction does neural tube closure proceed in?

A

Cranial and caudal directions

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12
Q

When does neural tube closure begin?

A

Day 18

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13
Q

When is neural tube closure complete?

A

Completed by end of 4th week (~day 27)

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14
Q

How many closure sites is there in the neural tube?

A

Up to 5 closure sites in humans

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15
Q

What does failure of the neural tube to close properly lead to?

A

Neural tube defects (NTDs)

  • Anencephaly
  • Encephalocele
  • Spina bifida
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16
Q

Who is affected by exencephaly/ anencephaly (meroencephaly)

A
  • 1:1500 births

- ~4x more common in females

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17
Q

What occurs in exencephaly/ anencephaly (meroencephaly)?

A
  • Failure of anterior neuropore to close leads to failure of skull formation and brain tissue degeneration
  • It is incompatible with life
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18
Q

Craniorachischisis

A

Failure of neural tuve closure along entire neuroaxis

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19
Q

How many people are affected by encephalocoele?

A

1:4000 births

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20
Q

What occurs in encephalocoele?

A
  • Herniation of cerebral tissue through a defect in the skull due to failure of the rostral neural tube to close
  • Results in variable degree of neurological deficits
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21
Q

What is the most frequent region involved in encephalpocoele?

A

Occipital region

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22
Q

What is spina bifida?

A
  • A condition where there is defective closure of the caudal neural tube which affects the tissues overlying the spinal cord
  • Neural tissue may or may not be affected and severity ranges from minor abnormalities to major clinical symptoms
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23
Q

What causes spina bifida?

A

Non-fusion of vertebral arches

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24
Q

What is the most minor form of spina bifida?

A

Spina bifida occulta

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25
Q

What causes spina bifida occulta?

A

Failure of embryonic halves of vertebral arch to grow normally and fuse

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26
Q

Where does spina bifida occulta usually occur?

A

Occurs in L5 and L6 vertebrae of 10% of otherwise healthy people

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27
Q

How does spina bifida occulta usually present?

A
  • Usually no clinical symptoms.

- May result in dimple with small tuft of hair.

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28
Q

What is spina bifida cystica?

A

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

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29
Q

What is spina bifida with meningocele?

A

Protrusion of meninges and cerebrospinal fluid

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30
Q

What is spina bifida with meningomyelocle?

A

Nerve roots and/or spinal cord included in the protruding sac

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31
Q

What is spinal bifida with myeloschisis?

A

Spinal cord in affected area open due to failure of neural folds to fuse

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32
Q

How many people are affected by spina bifida cystica?

A

1:1000 live births

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33
Q

What is the rarest form of spina bifida cystica?

A

Spina bifida with meningocele

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34
Q

What is the most severe form of spina bifida cystica?

A

Spina bifida with myeloschisis

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35
Q

What neurological deficits accompany spina bifida with meningomyelocle?

A

Loss of sensation and muscle paralysis

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36
Q

What is the area affected by spina bifida with meningomyelocle determines by?

A

Level of lesion

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37
Q

What is spina bifida with meningomyelocle often associated with?

A

Hydrocephalus

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38
Q

Why is incidence of congenital abnormalities decreasing in the UK?

A
  • Folic acid supplements

- Prenatal diagnosis

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39
Q

How effective are folic acid supplements?

A

400 µg/day can produce a 50-70% decrease in risk

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40
Q

What forms of prenatal diagnosis are there?

A
  • Maternal blood screening
  • Amniocentesis
  • Ultrasound
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41
Q

What abnormalities can be detected on ultrasound?

A
  • Anencephaly from 12 weeks

- Spina bifida from 16-20 weeks

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42
Q

What can be detected by amniocentesis?

A

High levels AFP in amniotic fluid

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43
Q

What can be detected by maternal blood screening?

A
  • 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.
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44
Q

What are the risk factors for congenital abnormalities?

A
  • Genetic predisposition
  • Nutritional (e.g. too little folate, too much vitamin A)
  • Environmental (e.g. hyperthermia; taking certain drugs – e.g. sodium valproate)
45
Q

What does the development of the brain vesicles start with?

A

Begins with closure of anterior neuropore (~day 25; 18 – 20 somite stage)

46
Q

What are the 3 primary brain vesicles called?

A
  • Prosencephalon
  • Mesencephalon
  • Rhombencephalon
47
Q

What are the 5 secondary brain vesicles called?

A
  • Telencephalon
  • Diencephalon
  • Mesencephalon
  • Metencephalon
  • Myelencephalon
48
Q

Where is the cephalic flexure found?

A

Between midbrain (mesencephalon) and hindbrain (rhombencephalon

49
Q

When does the cephalic flexure develop?

A

End of 3rd week

50
Q

When does the cervical flexure develop?

A

End of 4th week

51
Q

Where is the cervical flexure found?

A

Between hindbrain and spinal corrd

52
Q

When does the pontine flexure develop?

A

5th week

53
Q

Where is the pontine flexure found?

A

In hindbrain (between metencephalon and myelencephalon

54
Q

What does the caudal neural tube develop into?

A

Spinal cord

55
Q

What does the telencephalon develop into?

A
  • Cerebral hemispheres
  • Hippocampus
  • Basal ganglia
56
Q

What does the diencephalon develop into?

A
  • Thalamus
  • Hypothalamus
  • Pituitary gland
  • Pineal
57
Q

What does the mesencephalon develop into?

A
  • Midbrain

- Superior and inferior colliculi

58
Q

What does the metencephalon develop into?

A
  • Cerebellum

- Pons

59
Q

What does the myelencephalon develop into?

A

Medulla

60
Q

What does the lumen of the neural tube develop into?

A

Ventricular system

61
Q

What connects the lateral and III ventricle?

A

Foramina of Munro

62
Q

When does the CSF begin to form?

A

During 5th week

63
Q

What is the CSF produced by predominantly?

A

Choroid plexus (in III and IV, lateral ventricles)

64
Q

What does the CSF drain into?

A

Drains into subarachnoid space via openings in roof of 4th ventricle

65
Q

What is the CSF absorbed into?

A

Venous system

66
Q

What is hydrocephalus?

A

Accumulation of cerebral spinal fluid which results in enlarged brain and cranium

67
Q

What is hydrocephalus frequently due to?

A

Frequently due to blocked aqueduct which prevents CSF from lateral and 3rd ventricles passing into the 4th ventricle meaning it can’t drain properly.

68
Q

What can cause hydrocephalus?

A
  • Genetic
  • Prenatal viral infection
  • Intraventricular haemorrhage
  • Spina bifida cystica
69
Q

When does cellular differentiation in the neural tube take place?

A

Begins early embryogenesis, continues into postnatal period

70
Q

Give an example of a region which adds new cells throughout life?

A

Olfactory epithelium

71
Q

What is the neural tube initially?

A

Initially a single layer of rapidly dividing neuroepithelial cells

72
Q

What epithelium is found in the neural tube?

A

Pseudo stratified epithelium

73
Q

Where does the epithelium of the neural tube divide?

A

Ventricular surface

74
Q

What produces most cells of the CNS?

A

Neuroepithelium

75
Q

What are microglia?

A

Mesenchymal cells that migrate into CNS

76
Q

What can neuroepithelial cells form?

A
  • Ependymal cells
  • Neurons
  • Astrocytes
  • Ogliodendrocytes
77
Q

What is the sensory component of the spinal cord?

A

Dorsal root ganglia

78
Q

How does the position of the spinal cord change?

A
  • 3rd month – extends entire length of vertebral column.
  • Vertebral column and dura mater grow more rapidly leading to a cord at progressively higher levels (newborn, ~L2 or L3; adult ~L1).
79
Q

Where are the spinal nerves initially found?

A

Level of origin

80
Q

How is the cauda equine formed?

A

Spinal nerves become elongated

81
Q

What forms the terminal filum?

A

Pia mater

82
Q

What are the sympathetic and parasympathetic ganglia formed by?

A

Neural crest cells

83
Q

Ganglia

A

Collection of neuronal cell bodies

84
Q

Where are the parasympathetic ganglia found?

A

Near or within organs they innervate

85
Q

Where are the sympathetic ganglia found?

A

-Chains along side of spinal cord.
-Preaortic ganglia
-Sympathetic organ plexuses
(in e.g. heart, lungs, GI tract).

86
Q

How do sulci and gyri develop?

A
  • Surface of cerebral hemispheres initially smooth.
  • Rapid growth results in the development of sulci (grooves) and gyri (elevations).
  • Pattern becomes more complex as brain enlarges.
87
Q

What is lissencephaly?

A

Rare brain disorder where the gyri and sulci fail to develop

88
Q

What is lissencephaly caused by?

A

Defective neuronal migration

89
Q

How does lissencephaly present?

A
  • Severe mental impairment
  • Failure to thrive
  • Seizures
  • Abnormal muscle tone
90
Q

What is the prognosis of lissencephaly?

A

Many affected children die before age 10

91
Q

What is polymicrogyria?

A

Excessive number of small gyri

92
Q

How does polymicrohyria present?

A

Variable degree of neurological problems (e.g. mental retardation, seizures, motor deficits etc)

93
Q

What can cause microcephaly?

A
  • Genetic
  • Drugs
  • Infection (Zika virus)
94
Q

How does microcephaly present?

A
  • Intellectual impairment
  • Delayed motor -Functions/speech,
  • Hyperactivity
  • Seizures
  • Balance/co-ordination problems
95
Q

How does agenesis corpus callosum present?

A
  • Alone or with other cerebral abnormalities
  • Effects range from subtle – severe
  • Cognitive and social difficulties to intellectual impairment, seizures, hypotonia etc
96
Q

What is porencephaly usually caused by?

A
  • Postnatal stroke

- Infection

97
Q

How does porencephaly present?

A
  • Delayed growth and development
  • Seizures
  • Hypotonia
  • Intellectual impairment
98
Q

What can cause schizencephaly?

A
  • Genetic
  • In utero stroke
  • Infection
99
Q

How does schizencephaly present?

A
  • Paralysis
  • Seizures
  • Intellectual impairment
  • Developmental delay
100
Q

What is diastematomyelia?

A

Split cord malformation where the cord splits into 2 parts longitudinally

101
Q

What is diastematomyelia usually associated with?

A

Vertebral abnormalities

102
Q

How doe diastematomyelia present?

A
  • Scoliosis
  • Weakness of lower extremities
  • Hairy patch over lower back
  • Foot deformities
  • Loss of sensation
103
Q

What is often absent in intellectual impairment?

A

Gross brain defects

104
Q

What can cause intellectual impairment?

A
  • 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)
105
Q

What is most common cause of intellectual impairment?

A

Maternal alcohol abuse

106
Q

What is the incidence of foetal alcohol syndrome?

A
  • Foetal alcohol syndrome 1:1000

- Estimated up to 1:100 some degree of intellectual impairment

107
Q

What is porencephaly?

A

CSF filled cysts or cavities in the brain

108
Q

What is schizencephaly?

A

Large clefts or silts in the brain

Systems: Neurology AB (51 decks)

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