Neurology of the Newborn Flashcards
What are the 3 layers of cells in early embryologic development?
endoderm, mesoderm and ectoderm
What will the endoderm form?
the epithelium
What will the mesoderm form?
muscle and connective tissue
What will the ectoderm form?
skin and the nervous system
How does the CNS initially appear?
the ectoderm thickens and flattens to form the neural plate; one of the first systems to develop
When does the neural plate appear in embryologic development?
at the beginning of the 3rd week of life
How does the neural groove form?
the lateral edges of the neural plate elevate to form the neural folds, and subsequently creating a neural groove
What does fusion of the neural folds create?
the neural tube
When does the formation of the neural fold occur in embryologic development?
beginning of the 4th week of life; fusion occurs at the level of the 4th cervical vertebrae
In what direction does neural tube fusion occur?
proceeds from cephalad and caudal directions
What are neuropores?
fusion delayed at the cranial and caudal ends leaves openings at either pole
What do the neuropores create?
open communication between neutral tube and the amniotic cavity
When is the cranial neuropore expected to close?
on day 25 after conception
When is the caudal neuropore expected to close?
on day 27 or 2-3days after
What is the physiologic cause of a neural tube defect?
failure of the neural tube to close between 25-28 days after conception
What diagnosis accounts for most the CNS congenital anomalies?
NTD
How prevalent are NTD in the US?
second most common congenital anomaly (after CHD)
What are the risk factors for NTDs?
1) folic acid deficiency
2) maternal diabetes (poor glycemic control in the first trimester is a high risk factor)
3) Maternal exposure to certain medications (anticonvulsants and folic acid antagonists)
4) previous infants with NTDs
If a family had a child with a NTD, what is their risk for subsequent pregnancies?
with 1 child with a NTD, the risk is 2-4%; if > 1 child with a NTD, the risk is > 10%
What medications are associated with an increased risk for NTDs?
phenytoin, phenobarb, carbamazepine and trimetoprima
What is the greatest measure of NTD prevention?
folic acid supplementation before conception (1-3mo) and during the first month of pregnancy can prevent up to 70% of NTD cases.
What is the recommended doseage of folic acid?
0.4mg for normal women; mother’s at increased risk should take 4mg throughout their pregnancy
What are the different forms of NTDs?
1) Anencephaly
2) Encephalocele
3) Myelomeningocele
What is Anencephaly?
the most severe form of NTD, not compatable with life.
failure of the cephalic end of the neural tube to close and results in degredation of the forebrain
What is the extent of structural damage with an Anencephaly diagnosis?
absence of scalp, skull and brain tissue, may be able to visualize the brain stem, exposed hemorrhagic fibrotic tissue; may have brain stem sparing
How is Anencephaly diagnosed?
will have elevated maternal alpha fetoprotein; US 14-15 weeks GA
What is the rate of spontaneous abortion in infants with Anencephaly?
65%; most families elect to abort child
Why do infants with Anencephaly typically continue on into post term maturation?
pituitary and adrenal functions are important in triggering labor; these structures are typically underdeveloped and labor may subsequently occur spontaneously
What is the survival expectancy of infants with Anencephaly?
75% will be stillborn, other infants typically die within a few hours, days or a few weeks
What is the clinical presentation of infants with Anencephaly?
unconscious with varying degrees of brain stem function
What are the management strategies typically recommended for infants with Anencephaly?
comfort care, genetic consultation and maybe organ donation
Why are infants with Anencephaly not typically good organ donor candidates?
infants may not meet criteria for brain death until they deteriorated and their solid organs have been damaged
How does encephalocele occur?
failure of complete closure of anterior neural tube
What is an encephalocele?
herniation of meninges with or without brain tissue through a skull defect
Where do encephaloceles occur?
75% occipital; 90% midline; can also occur in the frontal, parietal or nasopharyngeal regions
What is the expected result of an encepholocele on the maternal alpha-fetoprotein level?
normal levels; lesion is covered by skin; only elevated in 3% of cases
How should an encephalocele be managed?
detailed maternal and family history, genetics consultation, surgery consultation (involved prior to delivery if known) and examination for associated anomalies
What is the percentage of comorbid anomalies associated with an encepholocele?
60%
What is the prognosis with an encephalocele?
depends on size, involved brain tissue and additional associated anomalies
What is the most common NTD?
spina bifida
What is the physiologic mechanism that causes spina bifida?
failure of the caudal neuropore to close
What are the three types of spina bifida?
1) spina bifida occulta
2) meningocele
3) myelomeningocele
What percentage of the population has spina bifida?
10-20%; most people are dx incidentally from a spinal xray
what is spina bifida occulta?
Spina bifida occulta is the mildest type of spina bifida. It is sometimes called “hidden” spina bifida. With it, there is a small gap in the spine, but no opening or sac on the back. The spinal cord and the nerves usually are normal. Usually doesn’t cause disabilities.
How does skin present with at the site of a spina bifida occulta lesion?
may be normal, hair tuft, skin dimple, hemangioma, lipoma or birth mark
What is a meningocele?
only involves the meninges bulging through the defect in the spinal column
What is a myelomeningocele?
herniation of meninges and nerve tissue through a defect in the spinal column
Where do myelomeningoceles most commonly present?
lumbo-sacral (75%)
What is the expect degree of paralysis with a myelomeningocele diagnosis?
depends on the level of the defect
What conditions are typically comorbid with a myelomeningocele?
Chiari malformation (90%) and hydrocephalus (84%)
How is a myelomeningocele diagnosed prenatally?
elevated AFP and US at 14-16 weeks GA
What considerations should be observed for the management of a myelomeningocele in the DR?
keep the area sterile; use non latex gloves (minimize the risk of latex sensitization); prevent heat loss, decrease pressure by maintaining infant in lateral or prone position; keep site moist
How should a myelomeningocele be managed?
look for other anomalies, HUS (hydrocephalus) and renal US (structural anomalies), multidisciplinary team, surgical repair, support family, genetics, treatment of hydrocephalus
When should fetal surgery occur for primary closure of a myelomeningocele in utero?
between 18-25 weeks
What are the results of primary closure in utero of a myelomeningocele?
1) reduced the risk of death and need for shunt placement during the first yr of life
2) improvement in a composite score for mental development and motor fx at 30 months of age
What is the prognosis of infants born with a myelomeningocele?
14% will not survive past 5 years; mortality of 35% in infants with brain stem dysfunction
Describe the ventricular system of the brain.
2 lateral ventricles that have a frontal and occiptal horn, the lateral ventricles open to the 3rd ventricle by the foramen of monroe. the 3rd ventricle is midlined and opens into the fourth ventricle through the acqueduct of Sylvius. The 4th ventricle will open into the subarachnoid space through the foramen of Luschke and magendie
What is the typical volume of CSF in term newborns?
50mL
What is the range of normal pressure within a newborn’s ventricular system?
8-10cm H2O
What is the rate of CSF production in a term neonate?
500 mL/day
Where is CSF produced?
by the choroid plexus which is present all of the ventricular system except the frontal and occipital horn of the lateral ventricles and the acqueduct system
How is CSF reabsorbed?
CSF will be absorbed with the arachnoid villi and enter the dural venous sinuses and returns to the vascular and lymphatic systems
What can cause anomalies in CSF flow?
) an imbalance to CSF inflow or outflow
2) obstruction to flow
3) barriers to reabsorption
4) inadequate production
What is hydrocephalus?
excessive accumulation of CSF either due to over production or failure of reabsorption
What are the 2 types of hydrocephalus?
communicating and non-communicating; either type can be congenital or acquired; other forms include hydrocephalus ex-vacuo and normal pressure hydrocephalus (affecting adults)
What is hydrocephalus ex-vacuo?
damage to the brain caused by traumatic stroke or injury