Embryology and Congenital Malformations Flashcards
The nervous system develops from what?
Embryonic ectoderm
The CNS appears when?
Beginning of week 3
What are the steps of neuralisation?
- Neural plate forms from thickening of the ectoderm anterior to the primitive node
- Neural folds form from the edges thickening and moving upwards
- Neural folds migrate towards each other and fuse at midline forming neural tube, which remains open at anterior and posterior ends
- Neural tube closure
What does the neural plate form from?
Thickening of the ectoderm anterior to the primitive node
Describe the process of neural tube closure?
- Initiated at several points along A-P axis
- Proceeds in cranial and caudal directions
- Begins on day 18 and is completed by end of 4th week (about day 27)
What does failure of the neural tube to close correctly lead to?
Failure to close properly leads to neural tube defects (NTDs):
- Anencephaly
- Encephalocoele
- Spina bifida
The are some of the most common congenital abnormalities of the CNS
How many closure sites of the neural tube are there in humans?
Up to 5
Describe the epidemiology of exencephaly/ancenephaly?
(incidence, sex)
1:1500 births (4x more common in females)
Describe the pathology of exencephaly/anencephaly?
Failure of anterior neuropore to close
Skull fails to form
Describe the prognosis of exencephaly/anencephaly?
Brain tissue degenerates, is incompatible with life
What is craniorachischisis?
Craniorachischisis = failure of neural tube closure along entire neuroaxis
Describe the epidemiology of encephalocoele?
(incidence)
1:4000 births
Describe the pathology of encephalocoele?
- Herniation of cerebral tissue through a defect in the skull
- Failure in closure of rostral neural tube
- Most frequently in occipital region
Describe the prognosis of encephalocoele?
Variable degree of neurological deficits
Describe the pathology of spina bifida?
- Defective closure of the caudal neural tube
- Affects tissues overlying the spinal cord
- Neural tissue may or may not be affected
What is spinda bifida?
Spina bifida = non-fusion of vertebral arches
Describe the prognosis of spina bifida?
Severity ranges from minor abnormalities to major clinical symptoms
What are the different kinds of spina bifida?
-
Spina bifida occulta
- Most minor form
- Failure of embryonic halves of vertebral arch to grow normally and fuse
- Occurs in L5 and L6 vertebrae
- Usually no clinical symptom
- May result in dimple with small tuft of hair
-
Spina bifida cystica
- Protrusion of spinal cord and/or meninges through the defects in vertebral arches
- 1:1000 births
- Different kinds
- Spina bifida with meningocele
- Rarest form
- Protrusion of meninges and CSF
- Spina bifida with meningomyelocle
- Nerve roots and/or spinal cord included in the sac
- Neurological deficits such as loss of sensation and muscle paralysis
- Area affected determined by level of lesion
- Often associated with hydrocephalus
- Myeloschisis
- Most severe form
- Spinal cord in affected area open due to failure of neural folds to fuse
- Spina bifida with meningocele
Spina bififa occulta - pathology
- Most minor form
- Failure of embryonic halves of vertebral arch to grow normally and fuse
- Occurs in L5 and L6 vertebrae
Spina bifida occulta - presentation
- Usually no clinical symptom
- May result in dimple with small tuft of hair
Spina bifida cystica - pathology
- Protrusion of spinal cord and/or meninges through the defects in vertebral arches
Spina bifida cystica - epidemiology (incidence)
- 1:1000 births
Spina bifida cystica - different kinds
- Spina bifida with meningocele
- Rarest form
- Protrusion of meninges and CSF
- Spina bifida with meningomyelocle
- Nerve roots and/or spinal cord included in the sac
- Neurological deficits such as loss of sensation and muscle paralysis
- Area affected determined by level of lesion
- Often associated with hydrocephalus
- Myeloschisis
- Most severe form
- Spinal cord in affected area open due to failure of neural folds to fuse
Is incidence of neurological congenital malformations increasing or decreasing? Why?
Incidence is decreasing in the UK due to:
- Folic acid supplements (400ug/day)
- Prenatal diagnosis
- Maternal blood screening
- Indicated by high levels of α-fetoprotein (AFP) in serum – AFP from foetal liver leaks into amniotic fluid then into maternal blood.
- Best detected 16-20 weeks
- Amniocentesis
- High levels of AFP in amniotic fluid
- Ultrasound
- Anencephaly from 12 weeks, spina bifida from 16-20 weeks
- Maternal blood screening
What are risk factors for neurological congenital malformations?
- Genetic predisposition
- Nutritional (such as too little folate, too much vitamin A)
- Environmental (such as hyperthermia, taking certain drugs)
What does development of brain vesicles begin with?
Begins with closure of anterior neuropore (about day 25, 18-20 somite stage)
What bends in the neural tube occur?
- Cephalic flexure
- End of 3rd week
- Between midbrain (mesencephalon) and hindbrain (rhomboencephalon)
- Cervical flexure
- End of 4th week
- Between hindbrain and spinal cord
- Pontine flexure
- 5th week
- In hindbrain (between metencephalon and myelencephalon)