OVERVIEW: What every practitioner needs to know
Are you sure you're patient has myelomeningocele? What are the typical findings for this disease?
Myelomeningocele is an open neural tube defect resulting from failure of proper neural tube closure during primary neurulation. As a result, the overlying dorsal mesenchymal elements (i.e. skin, muscle, bone) do not form, leaving an open defect. Prenatal diagnosis is often suspected based on secondary cranial findings (Lemon and Banana Signs) on ultrasound. Alternatively, the malformation is invariably identified at birth.
Chiari II Malformation:
Represents a complex constellation of abnormalities affecting the entire CNS.
Present in up to 95% of myelomeningocele patients.
Almost never present in patients without myelomeningocele.
Significant distinction from the more common Chiari I Malformation.
Presents in 60-80% of children with myelomeningocele. Rates of ventricular shunt dependence are variable.
What other disease/condition shares some of these symptoms?
Other forms of Spinal Dysraphism:
Less severe forms of spinal dysraphism include lipomyelomeningocele, myelocystocele, and meningocele.
What caused this disease to develop at this time?
The causes of myelomeningocele are likely multiple and largely unknown. The risk is increased in several situations:
Inadequate prenatal care, specifically lack of maternal folate supplementation, is associated with an increased risk of meningomyelocele.
Maternal history of a child with an open or closed neural tube defect is a risk factor with future pregnancies. This is 2-3% in the absence of folate therapy.
Infants born to mothers who take carbamazepine or valproic acid are increased risk (1%) of myelomeningocele.
What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?
Elevated maternal serum alphafetoprotein in early in second trimester of pregnancy is used as a screening test.
Would imaging studies be helpful? If so, which ones?
Prenatal Ultrasound to identify the abnormality.
Prenatal magnetic resonance imaging (MRI) – seldom necessary.
Postnatal imaging options include echocardiogram, renal ultrasound if the child is oliguric or anuric, cranial ultrasound examination to USG evaluate baseline ventricular size and a lateral lumbar spine radiograph to assess for gibbus deformity.
Confirming the diagnosis
High resolution prenatal ultrasound is almost 100% sensitive for neural tube defects. Confirmatory amniocentesis is rarely indicated. Prenatal MRI is more sensitive than ultrasound, but is not commonly necessary. Postnatal diagnosis is straightforward and does not require imaging or laboratory investigations.
If you are able to confirm the patient has meningomyelocele, what treatment should be initiated?
Maintain patient in prone position.
Keep the open defect moist. One can cover the open defect with soaking wet gauze and an occlusive material, e.g., plastic wrap or cellophane.
Operative closure of the defect within 72 hours of birth.
Prenatal closure is an option at some centers.
What are the adverse effects associated with each treatment option?
The risks of not closing the spinal defect include meningitis and death. Risks associated with closure of the defect include failure of the wound to heal, neurological injury, and symptomatic spinal cord tethering during childhood.
If the patient demonstrates clinically significant hydrocephalus, the risks of failing to treat this include neurological injury and death. Treatment most commonly is through ventriculo-peritoneal shunt placement. Risks of shunt placement include infection, shunt failure, intracranial hemorrhage, injury to the lungs, abdominal organs, or subclavian vessels.
What are the possible outcomes of myelomeningocele?
Prognosis is highly variable and influenced by the level of the congenital defect. Some patients are able to ambulate with assistive devices and are cognitively normal. Other patients are severely cognitively disabled and wheelchair bound.
Long term complications may be related to hydrocephalus, syringomyelia, kyphoscoliosis, or urological or other orthopedic complications.
What causes this disease and how frequent is it?
Incidence varies among countries. In the United States, current incidence is 0.44 per 1000 live births, which is approximately 2500-6000 cases per year.
Rates have decreased with maternal folate use and early prenatal diagnosis.
Additional Risk Factors may include maternal exposure to agricultural pesticides, cleaning solvents, radiation, hyperthermia, lead, and tobacco.
There are no specific genetic markers for myelomeningocele.
How do these pathogens/genes/exposures cause the disease?
The causative role of these agents is not understood.
What complications might you expect from the disease or treatment of the disease?
The most frequent neurological complications are related to hydrocephalus, however patients with myelomeningocele require long term surveillance by a multi-disciplinary team including neurosurgery, urology, orthopedics, and rehabilitation services. Children may develop respiratory complications related to the Chiari II malformation. There is also a risk of symptomatic spinal cord re-tethering and progressive kyphoscoliosis. As children reach their teens, the complications associated with urological dysfunction may become more prevalent, as adherence to clean intermittent catheterization regimens may decline.
How can myelomeningocele be prevented?
The most effective preventative therapy is maternal folate supplementation before and during pregnancy. In women who are at normal risk, the recommended dose is 0.4mg daily before pregnancy and 0.6mg daily during pregnancy. For women at increased risk (history of pregnancy with NTD, close relative or partner with NTD, VPA or CBZ treatment), the dose is 4mg daily both before and during pregnancy.
What is the evidence?
Dias, MS, Partington, M. “Embryology of myelomeningocele and anencephaly”. Neurosurg Focus. vol. 16.
McLone, D. “The cause of Chiari II malformation: A unified theory”. Pediatr Neurosci,. vol. 15. 1989. pp. 1-12.
“American Academy of Pediatrics Committee on Genetics: Folic acid for the prevention of neural tube defects”. Pediatrics,. vol. 104. 1999. pp. 325-327.
Greene, W, Terry, R, DeMasi, R. “Effect of race and gender on neurological level in myelomeningocele”. Dev Med Child Neurol. vol. 33. 1991. pp. 110
Shurtleff, D, Lemire, R. “Epidemiology, etiologic factors, and prenatal diagnosis of open spinal dysraphism”. Neurosurg Clin N Am,. vol. 6. 1995. pp. 183-193.
VanDorsten, J, Hulsey, T, Newman, R. “Fetal anomaly detection by second-trimester ultrasonography in a tertiary center”. Am J Obstet Gynecol,. vol. 178. 1998. pp. 742-749.
Kaufman, BA, Terbrock, A, Winters, N. “Disbanding a multidisciplinary clinic: effects on the health care of myelomeningocele patients”. Pediatr Neurosurg,. vol. 21. 1994. pp. 36-44.
Adzick, NA, Thorn, EA, Spong, CY. “A Randomized Trial or prenatal versus postnatal repair of myeloeningocele”. N Engl J Med. vol. 364. 2011 Mar 17. pp. 993-1004.
Ongoing controversies regarding etiology, diagnosis, treatment
Recent data indicates that shunt dependency and mental development and motor scores are better following prenatal rather than postnatal closure of myelomeningocele. The implications of this finding remain under evaluation. See:
Adzick, NA. “A Randomized Trial or prenatal versus postnatal repair of myeloeningocele”. N Engl J Med. vol. 364. 2011 Mar 17. pp. 993-1004.
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- OVERVIEW: What every practitioner needs to know
- Are you sure you're patient has myelomeningocele? What are the typical findings for this disease?
- What other disease/condition shares some of these symptoms?
- What caused this disease to develop at this time?
- Would imaging studies be helpful? If so, which ones?
- Confirming the diagnosis
- If you are able to confirm the patient has meningomyelocele, what treatment should be initiated?
- What are the adverse effects associated with each treatment option?
- What are the possible outcomes of myelomeningocele?
- What causes this disease and how frequent is it?
- How do these pathogens/genes/exposures cause the disease?
- What complications might you expect from the disease or treatment of the disease?
- How can myelomeningocele be prevented?
- What is the evidence?
- Ongoing controversies regarding etiology, diagnosis, treatment