Embryology and Congenital Malformations

Question 1

The nervous system develops from

Answer 1

the embryonic ectoderm

Question 2

At what week of development does the CNS appear?

Answer 2

At the beginning of the third week

Question 3

How are the neural plate and neural folds formed?

Answer 3

Thickening of ectoderm anterior to primitive node forms the neural plate, edges thicken and move upwards to form neural olds

Question 4

Neural folds migrate towards each other and fuse at the midline to form

Answer 4

the neural tube

Question 5

When does the anterior neuropore close?

Answer 5

18-20 somite stage, around 25 days

Question 6

When does the posterior neuropore close?

Answer 6

Around day 27

Question 7

The closure of the neural tube is essential for

Answer 7

normal development of and function

Question 8

Closure of the neural tube is completed by

Answer 8

the 4th week of development

Question 9

What are the most common defects which result from failure of the neural tube to close?

Answer 9

Anencephaly
Encephalocoele
Spina bifida

Question 10

Prevalence of Anencephaly

Answer 10

1:1500 births

Question 11

Is anencephaly more common in males or females?

Answer 11

Females

Question 12

Features of anencephaly

Answer 12

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

Question 13

What is craniorachischisis?

Answer 13

Failure of anterior neuropore and rostral neural tube to close

Question 14

Prevalence of Encephalocoele

Answer 14

1:4000 births

Question 15

Features of encephalocoele

Answer 15

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 16

Features of spina bifida

Answer 16

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

Question 17

Features of spina bifida occulta

Answer 17

Most minor form
Failure of embryonic halves of vertebral arch to grow normally and fuse
Occurs in L5 and L6 vertebrae of otherwise healthy people
Usually no clinical symptoms
May result in dimple with small tuft of hair

Question 18

Features of spina bifida cystica

Answer 18

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

Question 19

Features of spina bifida with meningocele

Answer 19

Rarest form

Protrusion of meninges and CSF

Question 20

Features of spina bifida with meningomyelocele

Answer 20

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 21

What is the most severe form of spina bifida with meningomyelocele?

Answer 21

Myeloschisis - spinal cord in affected area is open due to failure of neural folds to fuse

Question 22

What is hydrocephalus?

Answer 22

Accumulation of CSF which results in an enlarged brain and cranium

Question 23

How does a blocked aqueduct cause hydrocephalus?

Answer 23

Prevents CSF from lateral and third ventricles from passing into fourth ventricle so can’t drain properly

Question 24

Causes of hydrocephalus

Answer 24

Genetic
Prenatal viral infection or intraventricular haemorrhage
Spina bifida cystica

Question 25

Folic acid supplements decrease the risk of spina bifida by what percentage?

Answer 25

50-70%

Question 26

How is spina bifida diagnosed prenatally?

Answer 26

Maternal blood screening - high levels of alpha-fetoprotein in serum
Amniocentesis
Ultrasound

Question 27

Risk factors for spina bifida

Answer 27

Genetic predisposition
Nutritional - too little folate, too much vitamin A
Environmental - hyperthermia, sodium valproate

Question 28

What is genetic counselling?

Answer 28

Process by which patients/relatives at risk of an inherited disorder are advised of the outcomes and nature of the disorder, probability of transmitting it and the options open to them