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Spina Bifida, Part 1

Alex Vanspeybroeck, MD and Solomon Behar, MD
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23:02

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Sol and Alex discuss sacral dimples and their evaluation, the different types of spina bifida and ways to manage common issues in children with spina bifida.

Pearls:

  • The 3 most common presentations of spina bifida include a myelomeningocele, a meningocele and spina bifida occulta. The clinical manifestations of spina bifida depend on the location and severity of the lesion.

  • Prenatal ultrasounds, specifically 4D ultrasounds, are sensitive at picking up spina bifida in utero.

  • All women of childbearing age should be taking 400 micrograms of folic acid daily.  

 

  • What is Spina Bifida? The 3 main and most common types of defects in patients with spina bifida are:

    • Myelomeningocele: This defect is an open neural tube defect (myelo) which includes protrusion of the meninges through a vertebral defect (meningocele).

      • This is the most common form of spina bifida and therefore, clinically, most providers are familiar with some of the sequelae, which can include hydrocephalus and neurogenic bowel and bladder.

    • Meningocele: This defect is a fluid filled cyst covered with meninges, without spinal cord involvement.

      • Early intervention is indicated; but often, these children can be neurologically intact.

    • Spina Bifida Occulta: This defect is a lack of complete connection of the vertebral elements in the back.

      • Often, it is a few millimeter defect in the spinous processes and has no clinical significance. It is usually picked up as an incidental finding on back xrays that were obtained for another reason.

  • What are some clinical pearls for examining the backs of babies? If a dimple is present, try to probe it. If the dimple is below the level of the coccyx, superficial in nature and the baby is well appearing with normal lower extremity movement, than usually there is nothing to worry about. Additional imaging is indicated when the following are noted:

    • A dimple that is higher up and/or along the lumbar spine

    • Other spinal dysraphisms such as a prominent hemangioma, a patch of hair, a deeper dimple

Depending on the findings, some will do an ultrasound to visualize the end of the spinal cord and assess for vertebral defects. Some ultrasounds will be able to visualize the spinal cord elements. If the ultrasound is normal and the child is neurologically intact, no further imaging is needed. Others will skip the ultrasound and go straight for an MRI for more level of detail.

  • How is spina bifida diagnosed prenatally? While blood tests are still done to assess for markers spina bifida (such as an elevated AFP) and genetic diseases, such as Trisomy 21, ultrasound is the main way that spina bifida is diagnosed prenatally. 4D ultrasounds pick up most meningomyelocele. Fetal MRI can be used to follow up a finding found on ultrasound.  

    • A classic ultrasound finding is called the “lemon sign” and is suggested of hydrocephalus in myelomeningocele. If noted, this would lead to a perinatology referral for higher resolution ultrasound and/or fetal MRI. The lemon refers to the shape of the head in babies with hydrocephalus.

  • What is the relationship between folic acid and the development of spina bifida?  Historically, an association was made between folic acid deficiency and open neural tube defects. In the 1990s, foods in the US began to be fortified with increased folic acid. This resulted in a tremendous decrease in the epidemiology of spina bifida; pre-fortification rates of spina bifida were 1/1500 live births and post-fortification the rates are closer to 1/10,000 live births. Of course, there is more to it than just fortification as ultrasounds are much better and some families are electing to terminate pregnancies.  Race and ethnicity are also at play. African Americans have lower rates of spina bifida and Latinos have higher rates.  

    • The CDC recommends that all women of childbearing age take 400 micrograms of folic acid daily and continue this during pregnancy.  

      • If a women has given birth to a baby with an open neural tube defect, the recommendation is that she take 4 milligrams (4000 micrograms) during the next pregnancy to prevent recurrence.

      • In April of this year, the FDA approved fortification of corn masa. Masa is used by many Hispanic cultures to make tortillas and tamales and hopefully will have an effect of lowering rates of spina bifida in these populations.

Editor’s Note: Open neural tube defects (NTD) occur when the neural tube fails to close in early embryonic development. Depending on the location and severity of the lesion, different clinical pictures emerge. Spina bifida is just one type of NTD. The rates of all NTD have been lowered by folic acid fortification.

Mandatory fortification of foods exist in 53 countries; however, many of these regulations have not been implemented.

Crider KS et al.  Folic acid food fortification-its history, effect, concerns, and future directions.  Nutrients. 2011 Mar;3(3):370-84. PMID 22254102

  • What about genetics and spina bifida? There are three different genetic pathways currently being investigated in spina bifida. One of these pathways involves folic acid metabolism. Ultimately, spina bifida is a multifactorial disease where genetic, environmental and perinatal factors, including maternal health, are at play.     

  • How do you handle open NTD in the delivery room? To care for an open NTD in the delivery room, you should cover the defect with warm, sterile, saline soaked gauze and plastic wrap. The goal is to keep heat in place and control fluid losses. These babies are stabilized and taken to a center for neurosurgical intervention. If possible, operations to close the lesion are performed on day of life one. Prophylactic antibiotics, with either a third generation cephalosporin and ampicillin or gentamicin and ampicillin, are started at delivery and continue for a couple of days after the closure. Length of hospitalization depends on the complexity of the lesion. More severe complications include hydrocephalus requiring shunting, apneic spells and/or feeding difficulty.  

    • In many rural areas, in the US and abroad, closure is delayed with varying consequences; including meningitis and sepsis.

  • What is a Chiari malformation?  A Chiari malformation is a structural defect in the cerebellum in which parts of the cerebellum and brainstem herniate through the foramen magnum.  It may be related to pressure caused by hydrocephalus.  In children with myelomeningoceles, and therefore open back lesions since 19-22 weeks of pregnancy, there may be under-development in the posterior fossa making it too shallow to properly incase the cerebellum.  A Chiari malformation may result.

    • Symptoms of a Chiari malformation in a baby include weak cry, apnea spells and feeding problems.  Many of these resolve with time and/or neurosurgical intervention.

  • Why do some children with spina bifida get ventriculoperitoneal shunts (VPS)?  Most of the time, it is related to their Chiari malformations and the aqueducts are blocked. The open NTD creates forces that tether and pull the spinal cord down, CSF leaks in the uterus, there is a shallow posterior fossa, a Chiari malformation results and all of these thing can compress the 3rd and 4th ventricular systems leading to hydrocephalus.

    • The rates and techniques of VPS placement in patients with spina bifida varies between centers; many children are observed without VPS and checked with serial cranial ultrasounds and head circumferences.  

      • In babies with spina bifida and no shunts, observation is done by the pediatrician and by neurosurgery. In the pediatrician's office, these babies should be seen at least every 2 weeks for the first 2 months then 1 time per month after that, then at well child visit intervals. Head circumferences should be measured at each visit and concerning signs would be crossing percentiles on the growth chart and the clinic signs noted below.  Neurosurgery sees these babies at least monthly during the first 6 months of life and cranial ultrasound are obtained at each visit.  

        • If the baby has been discharged from the NICU without a shunt, there is about a 50/50 chance he/she will need a shunt in the first 6 months of life.  If an infant with spina bifida has not needed a VPS by 6 months, then he/she will probably not need one in the future.

        • Signs a baby with spina bifida may need a VPS include: enlarging head circumference, large anterior fontanelle, vomiting, lethargy, engorged scalp veins, poor feeding, weak cry and/or the sunset sign, in which the eyes look like the irises are going below the lower lid.

  • What is a tethered cord? A syrinx? A tethered cord arises when there is tension at the end of the spinal cord.  Normally, the spinal cord ends at L1 or L2.  A “low lying” cord refers to a cord that ends at L3 or L4 and may increase the risk of a tethered cord. A tethered cord can happen for a number of reasons:

    • A cord may get trapped in scar tissue from an original myelomeningocele repair causing tethering.

    • A closed NTD with an overlying lipoma, for example, may have a piece of the spinal cord attached to it and this causes tethering.

As the child grows, more tension is placed on the spinal cord and clinical changes may occur because the nervous tissues become affected. Children with low lying cords present clinical challenges.  In a neurologically intact child with a low lying, surgical intervention to untether the cord is debated as this procedure has its own risks. However, if the tethering gets worse, it is hard to know whether early intervention would have made a difference prior to the start of clinical symptoms. In general, most neurosurgeons opt for the conservative approach of observation. The exception to this is children with extremely low lying cords that end near the sacrum; these will almost always cause problems as the children grow and early surgical release of the cord is performed.

  • Clinical signs of tethered cords include:

    • Changes in lower extremity tone or sensation, changes in gait, a cavovarus or claw-like foot deformity, changes in baseline bowel or bladder function or worsening scoliosis.

  • Neuromuscular scoliosis occurs in kids with spina bifida and may be related to a syrinx. The syrinx, a lake of fluid within the spinal cord may grow, forcing changes within the spinal cord and influences the vertebrae as well.

    • If orthopedic intervention with spinal fusion is indicated, a full neurosurgical work up is also initiated as tethered cord release and/or investigation of a syrinx may be performed at the same time.

    • Clinical signs of syrinx depend on the location of the syrinx.  In a higher level syrinx you may find, changes in upper extremity sensation and weakness.  In a lower level syrinx, progressive thoracic or lumbar scoliosis or kyphosis is seen.    

      • VPS malfunction may be the root cause of a syrinx and shunt investigation is generally the first step in management..  

Lara A. -

Love this very informative session. Wondering one thing about Spina Bifida patients. We learnt to have "latex precautions" with these patients. Is that still the recommendation?

Solomon B., MD -

Lara- yes, latex precautions should still be done. Because of life long exposure to latex catheters (and sometimes gloves), patients with spina bifida can develop a sensitivity to latex. Thanks for listening!

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