Case 1 - Spina Bifida Flashcards
what is spina bifida
neural tube defect that results from a defect in the closure of the neural tube. anatomically, this results in the loss of the posterior wall of the spinal canal and the spinous process of the affected vertebrae. it ca occur anywhere along the spine
where does SB occur most
the lumbar region of the spine
why is folic acid important to take during pregnancy
it is vital for the closing of the posterior and anterior neurospores
what is the dose of folic acid for a pregnant woman
0.4mg. women who have already had a baby with SB should tale 4mg 1-3 months before pregnancy
what is SB occulta
it is the loss of the spinous process but with no obvious bulge.
there may be excess hair on the affected area of the skin.
what percentage of the population does SB occulta affect
10%
why is there hair on the skin of the affected site
excess CSF leaks out which has growth factors in it
what are the 3 types of SB cystica
- meningocele
- myelomeningocele
- rachischsis
what is the meningocele
a bulge of the meninges is visible, but the spinal cord remains in its normal anatomical location
what is a myelomeningocele
a bulge of the meninges is visible, and the spinal cord lies outside of the normal location, inside the bulge.
what is a myelomeningocele often associated with
an Arnold Chiari type 2 malformation
what is rachischsis
very severe form of SB where the spine may be completely open and is often associated with anencephaly
what is anencephaly
when the neural tube doesn’t close at the top therefore large part of the brain is missing
what is syringomyelia
dilation of the fluid filled cavity that runs down the centre of the spinal cord
epidemiology of myelomeningoceles
affects 1/2000 pregnancies
how is SB diagnosed
by testing the maternal serum alpha fetoprotein (MSAFP). this is the foetal alternative to albumin.
how is theMSAFP tested
at 16-18 weeks, a so maple of the mother’s blood is tested for MSAFP. this is made naturally by the foetus and the placenta. during pregnancy, a small amount of AFP normally crosses into the mothers blood stream.abnormally hight levels of AFP may indicate that the foetus has SB or another neural tube defect. it is not specific to SB.
what are normal levels of MSAFP
10ng/ml - 150ng/ml
what level with SB
2.5MoM
when is the ultrasound for SB carried out
18-20 week scan
how does valproate lead to SB
VPA exposure prevents morphological and biomechanical conversion of the caudal extreme of the PNP during late spinal closure. closure 5 facilitates neural fold apposition when completion of closure is imminent, such that its disruption in VPA-exposed embryos may lead to distal SB. closure defect in the anterior neural tube and embryonic folate metabolism is disrupted.
Teratogenic effect due to embryonic exposure to valproate action as inhibitor of histone deacetylases, disturbing the balance of protein acetylation and deacetylation, leading to neurulation failure
what is the lemon sign
refers to the shape of the foetal skull at ultra-sonogrpagy when the frontal bones lose their normal convex contour and appear flattened or inwardly scalloped.
how does a lemon sign occur
decrease in the intraspinal pressure with SB foetus causes the brain to shift downwards. this shift decreases the intracranial pressure which is reflected into the foetal cranium. the frontal bones are the most vulnerable to the deceased intracranial pressure and respond by flattening inward. as the foetus matures, the lemon sign disappears as the frontal bones are stronger and can withstand the pressure.
epidemiology of lemon sign
sign of Arnold Chiari Malformation type II and 90-98% of SB children have it
what is an Arnold Chiari Malformation
condition in which the brain tissue extends into the spinal canal. it occurs when part of the skull is misshapen or smaller than typical, pressing on the brain and forcing it downward.
what is ACM type I
develops as the skull and brain are growing. as a result, signs and symptoms do not occur until late childhood or adulthood
what is ACM type II
- the paediatric formation and presents art birth
- a greater amount of tissue extends into the spinal canal
- related to myelomeningocele as the backbone and spinal canal do not close properly
- the cerebellum, and brain stem tissue extend into the foramen magnum - the hole for the spinal cord
what gene causes the genetic type of ACM type II
FUZ gene
what is ACM type 3
the most severe type of condition
- a portion of the cerebellum, or the brainstem extends through the opening in the back of the skull
- higher mortality rate and causes neurological problems
what test is performed to differentiate between a meningocele and myelomeningocele
transillumination test
