Congenital Anomalies of the Central Nervous System Flashcards
What maternal hormone level between 16 and 18 weeks’ gestation identifies infants at high risk for neural tube defects?
An elevated materna serum α-fetoprotein level.
What drug taken during pregnancy greatly increases the risk of neural tube defects in the infant?
Valproic acid
What maternal supplement is used to reduce the risk of neural tube defects in the infant?
Folic acid. 50% or more of neural tube defects are prevented with periconceptional folic acid supplementation.
What is spina bifida?
It is a congenital defect in which a portion of the neural tube does not form properly. Symptoms vary depending on the type and the location of the lesion, but can include motor and/or sensory defects in the lower body, loss of bladder and bowel control, scoliosis, hydrocephalus, learning disabilities, and deformities of the hip, leg, and/or foot.
What are the three types of spina bifida?
Spina bifida occulta (mild effects, if any; very common), meningocele (moderate severity; rare), and myelomeningocele (very severe; most common).
Which type of spina bifida is most common?
Myelomeningocele
What is a meningocele?
It is the rarest form of spina bifida involving herniation of the meninges - but not the spinal cord - through a defect in the posterior vertebral arches.
What might one see on physical exam in a patient with a meningocele?
On transillumination along the vertebral column you might find a fluctuant midline mass, typically in the lower back. Most are covered with skin and pose no urgent problem.
Which meningoceles require immediate surgical intervention?
Children with CSF leaking from the meningocele or with incomplete skin covering need immediate surgical repair to prevent meningitis.
What family history finding increases the risk for development of myelomeningocele?
Risk increases with an increased number of affected siblings.
Which structures are involved in myelomeningoceles?
Nerve roots, spinal cord, meninges, vertebral bodies, and skin.
Where are myelomeningoceles most likely to occur?
They can be located anywhere along the neuraxis but are most commonly located in the lumbosacral region.
What is the general rule for estimating extent and degree of neurologic deficit based on the location of the myelomeningocele?
As a general rule, the lower the lesion is along the spine, the less severe the neurologic defects. The exception is the cervical and upper thoracic regions which, if affected, actually cause minimal neurologic manifestations.
What other neurological abnormality commonly accompanies myelomeningoceles?
Myelomeningoceles cause a downward displacement of the brain stem and cerebellar tonsils down into the spinal column, known as Chiari II malformation. This, in turn, causes an obstruction to normal CSF flow, with a resulting hydrocephalus occuring 85% of the time.
How is myelomeningocele usually treated?
Treatment involves a multidisciplinary team, with surgical repair usually occurring within the first few days of life. After repair, many infants require a VP shunt for ongoing management of hydrocephalus.
What GU abnormality should providers be on the lookout for in patients with myelomeningocele?
Pay special attention to the GU system and bladder catheterization because neurogenic bladder is common and easy to miss.
Describe spina bifida occulta.
Spina bifida occulta consists of a midline defect of the spinous processes without protrusion of the spinal cord or meninges. The defect is usually covered with skin and not obvious on external physical exam. The defect is relatively common and rarely causes any problems.
What can a patch of hair located at the lower back indicate?
Cutaneous markers such as a patch of hair, lipoma, skin-color changes, or a dermal sinus in the midline of the lower back may be the only indication of underlying spina bifida occulta and occur due to the abnormal neuroectodermal differentiation in that area.
What is the usual therapy for spina bifida occulta?
For symptomatic patients, surgical treatment is often warranted. Asymptomatic patients need close monitoring to evaluate for development of neurological or urological problems.
What is a dermoid sinus and what might its presence indicate?
A dermoid sinus presents as a small skin opening leading into a narrow duct below the skin. It sometimes has protruding hairs, a hairy patch, or a vascular nevus on the surface. It often occurs in association with spina bifida occulta. In the lumbar region, it can indicate the presence of a meningocele. In the occipital region, it can indicate the presence of an encephalocele.
What anatomic abnormality might one suspect in a patient with recurrent bacterial meningitis?
Occasionally, a dermoid sinus will pass through the dura and result in recurrent infections such as recurrent bacterial meningitis.
What is an encephalocele?
An encephalocele is a herniation of the brain, its coverings, or both through a skull defect.
Where do encephaloceles most commonly occur?
75% of the time, encephaloceles occur in the occipital region.
What finding correlates with neurological outcome in patients with encephalocele?
Significant brain tissue involvement correlates with poor neurological outcome, while the presence of only meninges is correlated with few, if any, neurological defects.
What is the treatment for encephalocele?
Prompt surgical removal of the sac and closure of the defect.
What is anencephaly?
In anencephaly, both cerebral hemispheres and large parts of the cranium are absent, with associated malformations of the face and eyes commonly occuring as well. It is a uniformly lethal condition.
What is the embryologic abnormality which leads to the development of anencephaly?
Anencephaly occurs due to failure of closure of the anterior neural tube (neuropore), which normally closes by 24 days postconception.
What dose of folic acid is recommended for women of childbearing age to prevent neural tube defects in their offspring?
The recommended dose is 0.4 to 0.8 mg of folic acid daily.
What folic acid dose should be used in women who are on anticonvulsant therapy or who have had a previous child affected with spina bifida?
These women should take 4mg/day of folic acid starting 1 month before attempting conception and continuing through the 1st trimester.
What is hydromyelia?
Hydromyelia is a symmetric dilation of the central canal of the spinal cord by CSF and typically communicates with the 4th ventricle.
