Embyrology And Congenital Malformations Flashcards
From which germ layer does the nervous system develop from?
Ectoderm
What forms the neural tube?
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
What are 3 neural tube defects and what are they caused by?
Caused by failure of the neural tube to close properly
- anencephaly
- encephalocoele
- Spina Bifida
What is encephalocoele?
Failure in closure of the anterior neural tube
Results in herniation of cerebral tissue through a defect in the skull
What is Spina Bifida?
Defective closure of the caudal end of neural tube
Non fusion of vertebral arches
What is the main difference in the pathology of Spina Bifida cystica with meningocele and meningomyelocle and myeloschisis?
Meningocele - protrusion of meninges and CSF
Meningomyelocle - protrusion of nerve roots and/or spinal cord
Myeloschisis - open spinal cord
What are risk factors for Spina Bifida?
Genetic predisposition
Nutritional i.e. folic acid, too much vitamin A
Environmental i.e. hyperthermia (high fever) Na valproate
What has a huge impact on decreasing the incidence in neural tube defects?
Folic acid supplements in pregnancy
How are neural tube defects detected in pregnancy?
Prenatal screening;
- maternal blood screening (AFP in serum)
- amniocentesis (AFP in amniotic fluid)
- USS
When can anencephaly be detected in pregnancy?
12 weeks
When can Spina Bifida be detected in pregnancy?
Weeks 16-20
What are the 3 primary brain vesicles?
Prosencephalon - forebrain
Mesencephalon - midbrain
Rhombencephalon - hindbrain
What are the 3 flexures of the developing brain and where do they occur?
Cephalon flexure - between midbrain and hindbrain (mesencephalon and rhombencephalon)
Cervical flexure - between hindbrain (rhombencephalon) and spinal cord
Pontine flexure - in hindbrain (rhombencephalon
What structures does the diencephalon give rise to?
Thalamus
Hypothalamus
Pituitary gland
Pineal gland
What structures does the telencephalon give rise to?
Cerebral hemispheres
Hippocampus
Basal ganglia
From what vesicle does the cerebellum and pons develop from?
Metencephalon
Hindbrain - rhombencephalon
From which vesicle does the medulla develop from?
Myelencephalon
Hindbrain - rhombencephalon
From which embryonic vesicle does the lateral ventricles develop from?
Telencephalon
From which embryonic vesicle does the 3rd ventricle develop from?
Telencephalon & diencephalon
From which embryonic vesicle does the cerebral aqueduct develop from?
Mesencephalon
From which embryonic structure does the 4th ventricle develops from?
Metencephalon & myelencephalon
What is hydrocephalus?
Accumulation of CSF resulting in an enlarged brain and cranium
What is hydrocephalus frequently due to?
Blocked cerebral aqueduct so the CSF cannot drain properly
What are the causes of hydrocephalus?
Genetic
Prenatal viral infections
Prenatal intraventricular haemorrhage
Spina Bifida cystica
What type of epithelium is the neuroepithlium?
Pseudostratified
Neuoepithelium produces most cells of the CNS except what cells?
Microglia
These are mesenchymal cells that migrate into the CNS
What type of cells form the PNS neurones and glia ?
Neural crest cells
What is the importance of cortical folding?
Saves space to minimise brain volume
Brings together brain regions that would otherwise be far apart so optimises brain wiring to functional organisation
What is lissencephaly ?
Smooth brain
Caused by defective neuronal migration
Results in severe mental impairement, failure to thrive, seizures and abnormal muscle tone
What is polymicrogyria?
Excessive number of small gyri
Neurological problems - mental retardation, seizures, motor deficits
What is the mild form of Spina Bifida?
Spina Bifida occulta
What vertebrae does Spina Bifida occulta occur in 10% of otherwise healthy people?
L5 and L6
