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Flashcards in Congenital malformations and mental retardation Deck (7)
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7 landmarks of nervous system development

-Neural tube closure: starts at day 22 and ends around day 28
-Outgrowth of telencephalic vesicles: 5th week
-Proliferation: occurs throughout development but mostly up to the end of the 2nd trimester
-Cell migration: begins 7 weeks and ends by 16 weeks
-Gyration: starts around week 24
-Myelination: begins at week 20
-Synaptic development: occurs throughout life


Neural tube closure defects: spina bifida

-3 types of spinal bifida
-Spina bifida occulta: bony defect in vertebra (usually lumbosacral) that can be silent. Can be associated w/ minor neurological defects and/or lower back pain
-Spina bifida meningocele: meninges herniate through the bony defect (can occur in the brain)
-Spina bifida myelomeningoceles: both meninges and CNS tissue herniate through the bony defect (in brain is called encephaloceles or hydroencephaloceles if it includes ventricle)



-Most severe manifestation of neural tube closure defect
-Due to lack of fusion of anterior neuropore, and thus no development of an overlying skull (leads to mechanical destruction of cerebrum)
-Children may be still born or born alive (if born alive only live a few hours)
-Folic acid deficiency is a known risk factor for neural tube defects
-Incidence: 1 in 5,000


Failure of diverticulation of telencephalic vesicles: holoprosencephaly (HPE)

-HPE is a defect in the forebrain and mid face that results in incomplete development and separation of midline structures
-Most severe is alobar HPE (usually incompatible with life): failure of forebrain to divide into left and right hemispheres. Also present w/ clefting of mid face, cyclopia
-Other less severe forms produce microcephaly, hypotelorism (close set eyes), single maxillary central incisor
-Incidence: 1 in 250 in embryogenesis, 1 in 16,000 newborns



-Almost all cases due to blockage of CSF flow (obstructive hydrocephalus)
-If obstruction occurs w/in the brain its a non-communicating hydrocephalus
-Most common causes of non-communicating hydrocephalus are: developmental malformation (aqueduct stenosis), inflammation, and neoplasm (ependymoma of 4th ventricle are examples), arnold chiari
-If obstruction occurs in subarachnoid space or arachnoid granulations its a communicating hydrocephalus (also includes CSF-secreting neoplasm: choroid plexus papilloma)
-Causes: subarachnoid hemorrhage, meningitis, and dural sinus thrombosis


Arnold-chiari malformation

-Malformation of the posterior fossa structures, causing herniation of cerebellar tissue (vermis) through foramen magnum and often misplaced medulla and 4th ventricle
-Downward displacement of brainstem
-Pts can develop obstructive hydrocephalus in 2 sites: foramen magnum or aqueduct of sylvius
-This is a non-communicating hydrocephalus
-Chiari type I: low lying cerebellar tonsils


Mental retardation

-Defined as significantly sub-average intelligence (IQ less than 70) with concurrent deficits in adaptive behavior (communication, social skills, work) and onset during developmental period
-Overal prevalence is 2-3% of population
-Prenatal factors: chromosome abnormalities, metabolic and nutritional problems, congenital infections, drug exposure
-Perinatal factors: prematurity, small size, bleeding in germinal matrix
-Postnatal factors: severe infections of CNS, lead or mercury poisoning, asphyxia

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