Fetal Anomalies Flashcards
primary neurulation
*days 18-24
*lateral margins of neural plate thicken to form neural folds
*neural folds contact each other, forming a neural tube (future brain and spinal cord)
*starts in cervical region
*rostral opening (anterior neuropore) closes first, usually by day 24
disorders of primary neurulation (dysraphic defects)
-anencephaly
-encephalocele
-chiari malformation
-spina bifida
causes of disorders of primary neurulation
*folic acid deficiency
*drugs (valproic acid, carbamazepine)
*genetic defects
detection of disorders of primary neurulation
can be detected by high FAP (fetal alpha protein) during the triple screen done during pregnancy
anencephaly
*absence of the brain (cortex); cerebral hemispheres missing
*occurs when the cranial neuropore does not close
*all brainstem reflexes intact, plus spinal cord, etc
*usually diagnosed in prenatal ultrasound
*rarely live for more than a few weeks/months
encephalocele
*cyst herniating through skull defect (commonly, herniation of brain/meninges through a defect in the occipital bone)
*clinical results: developmental delay and seizures
*several types (meningocele, meningoencephalocele, meningohydroencephalocele)
spina bifida - overview
*neural tube defect involving the vertebrae, in which the dorsal vertebral arch is incomplete
*a spectrum in which only the more severe forms include abnormal development of the spinal cord
*from least to most severe: spina bifida occulta, spina bifida aperta (meningocele, meningomyelocele)
spina bifida occulta
*most common, least severe neural tube defect
*bony defect (cleft) in one or more vertebral arches
*spinal cord and meninges are normal
*no neurologic deficits; patients are asymptomatic
meningocele
*a type of spina bifida aperta
*occurs when the meninges herniate through a cleft in the vertebral arches
*spinal cord and nerves are NOT involved
*mild neurologic deficits often present
meningomyelocele
*a type of spina bifida aperta
*occurs when both the meninges and SPINAL CORD herniate through a cleft in the vertebral arches
*the herniated spinal cord and attached spinal nerves are malformed, resulting in significant neurologic deficits (usually, sensory + motor loss below the level)
chiari type II malformation (Arnold-Chiari)
*herniation of the medulla, cerebellar tonsils, and cerebellar vermis caudally through the foramen magnum
*may cause hydrocephalus
*often associated with meningomyelocele!!
what other condition is commonly associated with meningomyelocele
Chiari malformation, type II
communicating hydrocephalus
*CSF can circulate through the ventricles but is not being reabsorbed into the venous system
*buildup of fluid on the outsude
obstructive (non-communicating) hydrocephalus
*obstruction of outflow of CSF (usually, blockage of the cerebral aqueduct)
*buildup of fluid on the inside of the brain, eventually pushing down on the brainstem
clinical presentation of meningomyelocele
*below the level of the malformation:
-weakness
-sensory loss
-loss of bowel/bladder and sexual function
prosencephalization
*4th-5th week
*primary brain vesicles form (prosencephalon [forebrain], mesencephalon [midbrain], rhombencephalon [hindbrain])
*prosencephalon flexes and divides into telencephalon & diencephalon
*end of 5th week:
-telencephalon gives rise to 2 telencephalic (cerebral) vesicles that eventually form the cerebral hemispheres
-diencephalon forms thalamic nuclei and associated structures
disorders of prosencephalization
*holoprosencephaly (alobar, semilobar, lobar)
*septo-optic dysplasia
causes of disorders of prosencephalization
*genetic (ex. trisomy 13 and 18)
*alcohol
*maternal diabetes
*TORCH infections (toxoplasma, rubella, CMV, herpes, HIV)
holoprosencephaly
*a spectrum of median brain anomalies arising when the telencephalon fails to partially or completely divide into 2 hemispheres
*ranges from lobar to semilobar to alobar
*usually associated with facial abnormalities
lobar holoprosencephaly
2 main lobes, but not completely separated (mildest version)
semilobar holoprosencephaly
frontal lobes are not really separated, but temporal and occipital lobes are
alobar holoprosencephaly
no separation of the 2 hemispheres (most severe version)
septo-optic dysplasia
*absence of septum pellucidum
*absence or hypoplasia of optic nerve (blindness or visual impairment)
*hypoplasia of pituitary (may cause pituitary insufficiency)
*often associated with other brain malformations (esp schizencephaly)
cortical development
*weeks 4-28
*immature neurons are formed in germinal matrix (ventricular zone)
*waves of these neurons migrate along radial glia to surface of brain
*“inside-out” pattern, with inner layers formed first, outer layers formed last
disorders of cortical development
- disorders of cellular proliferation (primary microcephaly; hemi-megalencephaly)
- disorders of neural migration (gray matter heterotopia; lissencephaly; schizencephaly)
disorders of cellular proliferation during cortical development
*primary microcephaly
*hemi-megalencephaly
disorders of cellular migration during cortical development
*gray matter heterotopia
*lissencephaly
*schizencephaly
primary microcephaly
*abnormally small brain volume, and therefore a small head circumference
*occurs when too few neurons reach the cerebral cortex
*genetic (not due to injury or infection)
*structure of brain looks superficially normal
*high risk of seizures
secondary microcephaly
*abnormally small brain volume, and therefore a small head circumference
*due to injury, infection, or drugs after initially normal cortical development
hemi-megalencephaly
*too many neurons formed on one side of the brain (other side of the brain is normal)
*very highly epileptogenic
*weakness on contralateral side
gray matter heterotopia
*clusters of neurons get “stuck” in the white matter on its way to cortex
*usually does not cause structural defects
*tends to be very epileptogenic (seizures)
lissencephaly
*smooth brain (too few gyri)
*occurs when neuronal migration stops prematurely
*all of the neurons “get stuck” and fail to form gyri
*associated with seizures
schizencephaly
*neurons fail to migrate to one area of cortex, forming a cleft
*open lip = if cleft extends to ventricle
*closed lip = if cleft does not extend to ventricle
