Fetal Anomalies

Question 1

primary neurulation

Answer 1

*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

Question 2

disorders of primary neurulation (dysraphic defects)

Answer 2

-anencephaly
-encephalocele
-chiari malformation
-spina bifida

Question 3

causes of disorders of primary neurulation

Answer 3

*folic acid deficiency
*drugs (valproic acid, carbamazepine)
*genetic defects

Question 4

detection of disorders of primary neurulation

Answer 4

can be detected by high FAP (fetal alpha protein) during the triple screen done during pregnancy

Question 5

anencephaly

Answer 5

*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

Question 6

encephalocele

Answer 6

*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)

Question 6

spina bifida - overview

Answer 6

*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)

Question 7

spina bifida occulta

Answer 7

*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

Question 8

meningocele

Answer 8

*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

Question 9

meningomyelocele

Answer 9

*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)

Question 10

chiari type II malformation (Arnold-Chiari)

Answer 10

*herniation of the medulla, cerebellar tonsils, and cerebellar vermis caudally through the foramen magnum
*may cause hydrocephalus
*often associated with meningomyelocele!!

Question 11

what other condition is commonly associated with meningomyelocele

Answer 11

Chiari malformation, type II

Question 12

communicating hydrocephalus

Answer 12

*CSF can circulate through the ventricles but is not being reabsorbed into the venous system
*buildup of fluid on the outsude

Question 13

obstructive (non-communicating) hydrocephalus

Answer 13

*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

Question 14

clinical presentation of meningomyelocele

Answer 14

*below the level of the malformation:
-weakness
-sensory loss
-loss of bowel/bladder and sexual function

Question 15

prosencephalization

Answer 15

*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

Question 16

disorders of prosencephalization

Answer 16

*holoprosencephaly (alobar, semilobar, lobar)
*septo-optic dysplasia

Question 17

causes of disorders of prosencephalization

Answer 17

*genetic (ex. trisomy 13 and 18)
*alcohol
*maternal diabetes
*TORCH infections (toxoplasma, rubella, CMV, herpes, HIV)

Question 18

holoprosencephaly

Answer 18

*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

Question 19

lobar holoprosencephaly

Answer 19

2 main lobes, but not completely separated (mildest version)

Question 20

semilobar holoprosencephaly

Answer 20

frontal lobes are not really separated, but temporal and occipital lobes are

Question 21

alobar holoprosencephaly

Answer 21

no separation of the 2 hemispheres (most severe version)

Question 22

septo-optic dysplasia

Answer 22

*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)

Question 23

cortical development

Answer 23

*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

Question 24

disorders of cortical development

Answer 24

1. disorders of cellular proliferation (primary microcephaly; hemi-megalencephaly)
2. disorders of neural migration (gray matter heterotopia; lissencephaly; schizencephaly)

Question 25

disorders of cellular proliferation during cortical development

Answer 25

*primary microcephaly
*hemi-megalencephaly

Question 26

disorders of cellular migration during cortical development

Answer 26

*gray matter heterotopia
*lissencephaly
*schizencephaly

Question 27

primary microcephaly

Answer 27

*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

Question 28

secondary microcephaly

Answer 28

*abnormally small brain volume, and therefore a small head circumference
*due to injury, infection, or drugs after initially normal cortical development

Question 29

hemi-megalencephaly

Answer 29

*too many neurons formed on one side of the brain (other side of the brain is normal)
*very highly epileptogenic
*weakness on contralateral side

Question 30

gray matter heterotopia

Answer 30

*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)

Question 31

lissencephaly

Answer 31

*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

Question 32

schizencephaly

Answer 32

*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