Embryology and Congenital Malformations Flashcards
what does the nervous system develop from?
embryonic ectoderm
when does gastrulation start?
week 3
when does the CNS appear?
beginning of week 3
what is the thickening of ectoderm anterior to the primitive node called?
neural plate
the edges of the neural plate thicken and move upwards to for the…
neural folds
neural folds migrate towards eachither and fuse at midline forming the…
neural tube
when dies tge anterior neuropore close at?
18-20 somite stage, 25 days
when does the posterior neuropore close?
day 27
with failure of neural tube to close properly results in neural tube defects. Give some examples
Anencephaly
Encephalocoele
Spina bifida
what is Exencephaly/Anencephaly(Meroencephaly
Failure of anterior neuropore to close.
Skull fails to form
Brain tissue degenerates.
Incompatible with life.
what is Encephalocoele
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.
what is spina bifida?
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.
what can spina bifida occulta result in?
dimple with small tuft of hair
what is spina bifida cystica?
Protrusion of spinal cord and/or meninges through the defect in the vertebral arches
what is Spina bifida with meningocele
Rarest form
Protrusion of meninges and cerebrospinal fluid
what is Spina bifida with meningomyelocle
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
how would you prevent congenital malformations?
Folic acid supplements (400 µg/day 50-70% decrease in risk)
what are the prenatal diagnosises?
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)
what are some risk factors for congenital malformation
Genetic predisposition
Nutritional (e.g. too little folate, too much vitamin A)
Environmental (e.g. hyperthermia; taking certain drugs – e.g. sodium valproate)
when does the Cephalic flexure form? and where does it form?
End of 3rd week. Between midbrain (mesencephalon) and hindbrain (rhombencephalon).
when does the Cervical flexure form and where?
End of 4th week.
Between hindbrain and spinal cord.
when does the pontine flexure form and where?
5th week.
In hindbrain
(between metencephalon and myelencephalon).
when does the CSF form?
during 5th week
what is Hydrocephalus
Accumulation of cerebral spinal fluid
Results in enlarged brain and cranium
Frequently due to blocked aqueduct
what are the causes of Hydrocephalus
genetic, prenatal viral infection or intraventricular haemorrhage, spina bifida cystica
what forms the PNS, neurons and ganglia?
Neural crest
what causes Lissencephaly ?
Caused by defective neuronal migration.
what is Lissencephaly
smooth brain, gyri and sulci fail to develop
what does Lissencephaly result in?
severe mental impairment, failure to thrive, seizures, and abnormal muscle tone.
what is Polymicrogyria
Excessive number of small gyri.
what is the result of Polymicrogyria
mental retardation, seizures, motor deficits etc)
what is Porencephaly
CSF filled cysts
or cavities
what causes Porencephaly
Usually from postnatal stroke or infection
what is the result of Porencephaly
Delayed growth and development, seizures, hypotonia, intellectual impairment
what is Aegenesis corpus callosum
there is a complete or partial absence of the corpus callosum
what does Aegenesis corpus callosum result in?
Cognitive and social difficulties—-> intellectual impairment, seizures, hypotonia etc
what is Schizencephaly
Large clefts or slits
what is the cause of Schizencephaly
Genetic, in utero stroke, infection
what does Schizencephaly result in?
Paralysis, seizures, intellectual impairment, developmental delay.
what is Diastematomyelia
Spinal cord split longitudinally into 2 parts
what does Diastematomyelia result in?
Scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation.
what are the causes of intellectual impairment?
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
