Spina Bifida Family Support
"Families Helping Families"
This information was derived from EMedicine.com. Author: Richard G Ellenbogen, MD, Chief, Division of Pediatric Neurological Surgery, Children's Hospital of Seattle; Theodore S Roberts Endowed Chair, Associate Professor, Department of Neurological Surgery, University of Washington School of Medicine
What is Spina Bifida
The 2 major types of defects seen with spina bifida cystica are myelomeningoceles and meningoceles. Cervical and thoracic regions are the least common sites, and lumbar and lumbosacral regions are the most common sites for these lesions.
Myelomeningocele is a condition in which the spinal cord and nerve roots herniate into a sac comprising the meninges. This sac protrudes through the bone and musculocutaneous defect. The spinal cord often ends in this sac in which it is splayed open, exposing the central canal. The splayed open neural structure is called the neural placode. This type of NTD is the subject of most of this article. Certain neurologic anomalies, such as hydrocephalus and Chiari II malformation (discussed later in this article), accompany myelomeningocele. In addition, myelomeningoceles have a higher incidence of associated intestinal, cardiac, and esophageal malformations, as well as renal and urogenital anomalies. Most neonates with myelomeningocele have orthopedic anomalies of their lower extremities and urogenital anomalies due to involvement of the sacral nerve roots.
A meningocele is simply herniation of the meninges through the bony defect (spina bifida). The spinal cord and nerve roots do not herniate into this dorsal dural sac. These lesions are important to differentiate from a myelomeningocele because their treatment and prognosis are so different from myelomeningocele. Neonates with a meningocele usually have normal examination findings and a covered (closed) dural sac. Neonates with meningocele do not have associated neurologic malformations such as hydrocephalus or Chiari II.
A subtype of spina bifida is called lipomeningocele, or lipomyelomeningocele, which is a common form of NTD treated by pediatric neurosurgeons. These lesions have a lipomatous mass that herniates through the bony defect and attaches to the spinal cord, tethering the cord and often the associated nerve roots. The lipomyelomeningocele can envelop both dorsal and ventral nerve roots, only the dorsal nerve roots, or simply the filum terminale and conus medullaris. These lesions do not have associated hydrocephalus but have a more guarded prognosis than simple meningoceles. The surgical correction of these lesions is more complex, and the retethering rate in which an additional surgery is required is as high as 20% in some series.
In a third rare type of spina bifida cystica called myelocystocele, the spinal cord has a large terminal cystic dilatation resulting from hydromyelia. The posterior wall of the spinal cord often is attached to the skin (ectoderm) and is undifferentiated, thus giving rise to a large terminal skin-covered sac. The vast majority of the lesions are dorsal, although a small minority (approximately 0.5%) are ventral in location. The most common ventral variant is an anterior sacral meningocele, which most often is discovered in females as a pelvic mass.
Spina bifida occulta
In this group of NTDs, the meninges do not herniate through the bony defect. This lesion is covered by skin (ie, closed), therefore rendering the underlying neurologic involvement occult or hidden. These patients do not have associated hydrocephalus or Chiari II malformations. Often, a skin lesion such as a hairy patch, dermal sinus tract, dimple, hemangioma, or lipoma points to the underlying spina bifida and neurologic abnormality present in the thoracic, lumbar, or sacral region. Presence of these cutaneous stigmata above the gluteal fold signifies the presence of an occult spinal lesion. Dimples below the gluteal fold signify a benign, nonneurologic finding such as a pilonidal sinus. This is an important point for differentiating the lesions that have neurologic involvement from those that do not.
An experienced pediatrician or surgeon should examine any neonate with cutaneous stigmata on the back around the gluteus. A good rule of thumb is that a lesion (eg, pit, tract) below the gluteal crease is often a pilonidal sinus and needs no further evaluation. Those tracts, pits, or lesions above the gluteal fold should be evaluated with further study.
Lesions that are questionable can be scanned with ultrasound in a neonate or with MRI in an older child. The ultrasound or MRI delineates the presence or absence of a tethered cord or other spinal anomaly. Plain radiology can reveal a panoply of anomalies, such as fused vertebrae, midline defects, bony spurs, or abnormal laminae. An MRI often is useful in evaluating for a split cord malformation (ie, diastematomyelia), in which a bony spur splits the spinal cord, or a duplication of the spinal cord and nerve roots (diplomyelia). More commonly, the neurosurgeon is searching for tethering of the spinal cord by a sinus tract or thickened filum that can cause traction on the spinal cord with subsequent neurologic deficits as the child grows.
A growing body of evidence indicates that the surgical repair of these lesions is more effectively performed in a prophylactic fashion. Once the patient experiences a significant neurologic deficit such as a neurogenic bladder or leg weakness from these occult spinal lesions, the surgical remedy may not return the patient to previous neurologic status.
Signs and symptoms of occult spinal disorders in children include the following:
Widening of interpedicular distance
Weakness of leg or legs
Leg atrophy or asymmetry
Loss of sensation, painless sores
Unusual back pain
Several types of midline skull defects are classified under this term, ranging from simple, with minimal clinical significance, to serious life-threatening conditions. The most benign type of cranium bifidum occultum is the persistent parietal foramina or persistent wide fontanelle. The parietal foramina can be transmitted as an autosomal dominant trait via a gene located on the short arm of chromosome 11. The condition is sometimes called "Caitlin marks," after the family for which it was described. Both parietal foramina and a persistent anterior fontanelle are generally asymptomatic and a pediatric neurosurgeon may be asked to evaluate the child for skull fracture, craniosynostosis, or some other reason related to these findings. The best management is observation over time, as these skull defects often close over time.
Cranium bifidum such as an encephalocele is much more serious. Encephaloceles are theorized to occur when the anterior neuropore fails to close during days 26-28 of gestation. Incidence of this anomaly is 10% of the incidence of spina bifida cystica. In the United States, approximately 80% of lesions are found on the dorsal surface of the skull, with most near the occipital bone. In contradistinction, most encephaloceles in Asia are ventral and involve the frontal bone. In the Philippines and other Pacific countries, incidence of anterior encephaloceles that present as hypertelorism, obstructed nares, anterior skull masses, and cleft palate, among other presentations, is high. In most lesions, the sac that has herniated through a midline skull defect is covered with epithelium.
A small number of encephaloceles are associated with syndromes such as Meckel-Gruber syndrome. This syndrome is characterized by an occipital encephalocele that is associated with holoprosencephaly, orofacial clefts, microphthalmia, polycystic kidneys, and cardiac anomalies. This condition is autosomal recessive and has been mapped to chromosome bands 17q21-q24. In the United States, only about 30% of occipital encephaloceles contain cerebral cortex. The rest contain cerebellar tissue, dysplastic tissue with little normal function, glial tissue, or are simple meningeal sacs filled with CSF (as in cranial meningocele).
An MRI is invaluable in planning a surgical approach. The surgeon needs to know the contents of the sac, which can be quite large. In addition, the surgeon needs to know the relationship of the major cerebral venous sinuses to the sac in order to plan a safe operative approach. Finally, the surgeon needs to know if the patient has hydrocephalus. Approximately 60% of these patients require placement of a ventricular peritoneal (VP) shunt after the removal of their encephalocele. Children whose encephaloceles contain large quantities of cerebral cortex often become microcephalic and display significant developmental and learning disabilities.
Presence of open NTDs can be detected with the measurement of AFP in the amniotic fluid or maternal bloodstream. AFP is the major serum protein in early embryonic life and is 90% of the total serum globulin in a fetus. It is believed to be involved in preventing fetal immune rejection and is first made in the yolk sac and then later in the gastrointestinal system and liver of the fetus. It goes from the fetal blood stream to the fetal urinary tract, where it is excreted into the maternal amniotic fluid. The AFP also can leak into the amniotic fluid from open NTDs such as anencephaly and myelomeningocele in which the fetal blood stream is in contact with the amniotic fluid.
The first step in prenatal screening is drawing the maternal AFP between 15 and 20 weeks of gestation. A patient-specific risk then is calculated based on gestational age and AFP level. Normal AFP concentration in the maternal serum is usually lower than 500 ng/mL. Determining precise gestational age is essential because fetal AFP levels are age specific and can peak in a normal fetus at 12-15 weeks of gestation. For example, at 20 weeks’ gestation, a maternal serum AFP concentration higher than 1,000 ng/mL would be indicative of an open NTD. The measurement of maternal serum AFP levels is more than 75% accurate in detecting an open NTD at more than 15 weeks of gestation. In patients in whom a question persists, amniotic AFP can be obtained. It is a significantly more accurate test, especially at 15-20 weeks’ gestation, and detects approximately 98% of all open NTDs, although this method is not the preferred screening test. Amniotic fluid acetylcholinesterase levels add an increased degree of resolution.
Detection of an NTD with fetal ultrasound in the hands of a skilled ultrasonographer usually is 98% specific. False-positive findings can result from multiple pregnancies or inaccurate fetal dating. However, closed NTDs also can sometimes remain undetected, especially in cases of skin-covered lipomyelomeningoceles and meningoceles, in which the AFP also may be normal. These closed NTDs comprise about 10% or more of total NTDs discovered. A skilled ultrasonographer can detect these lesions with almost 95% sensitivity.
Major issues in evaluating the outcome of children with myelomeningocele are hydrocephalus, intellect, ambulation, continence, orthopedic problems, and employment and independent living status.
Treatment of NTDs in neonates has evolved over the past half century. Historically, there was a period when neonates with NTDs were either left untreated or selectively treated. The natural history of neonates with NTDs left untreated is poor. Most died of meningitis, hydrocephalus, and sepsis. Laurence described a cohort of 290 children with spina bifida (mostly myelomeningoceles) left untreated in Wales during the 1950s and 1960s. Only 11% of those children lived past the first decade of life. Lorber and Salfield reported their results with selected treatment of neonates with myelomeningocele. More than 80% of the selected neonates lived, whereas 97% of the neonates denied treatment died in the first year of life. The tremendous ethical implications of selected neonatal treatment led to its abandonment.
In the United States during the 1960s, most children with myelomeningocele were treated, which resulted in a higher survival rate (>80% for the first decade) than that in Great Britain. Recognized causes of death include shunt malfunctions, seizures, infections, and uncontrolled brainstem symptoms from CM II and/or hydrocephalus. During the past 3 decades, aggressive treatment of neonates with myelomeningocele has been pursued in almost all pediatric centers in the United States.
Cognitive ability is, in part, influenced by hydrocephalus, CNS infections, and degree of impairment. In most series, 60-70% of the children with myelomeningocele had intelligence quotients (IQs) greater than 80; the others had IQs in the delayed or severely delayed range. In the McLone series, children who had CNS infections such as ventriculitis, or shunt infections fared worse than those who did not. Children with myelomeningocele without hydrocephalus had an average IQ of 102; those with hydrocephalus had an average IQ of 95. However, the average IQ dropped to 73 when a CNS infection complicated the picture. Children with moderate physical impairments, in most series, have a better intellectual outcome than those with significant sensory levels and paraplegia. The reasons most likely are multifactorial.
Only 10-15% of all children with myelomeningoceles are continent of urine. This issue often causes the children to be separated from their peers, which, in turn, leads to other neuropsychologic deficits. Despite the development of catheters and Crede manipulation (pushing on the pelvis over the bladder to engender urination), children with NTDs still experience a high rate of infections, vesicoureteral reflux, kidney failure, hydronephrosis, and obstruction. Clean intermittent catheterization (CIC) has led to a marked improvement of the lifestyles and lifespan of these children. CIC can make more than 75% of these children socially continent and significantly decreases the rate of urosepsis. As a result of CIC, urinary diversions are less commonly performed. Use of anticholinergic drugs combined with CIC has resulted in a better self-image and greater educational and vocational opportunities for children with NTDs.
Bowel continence is achieved with a combination of medication, diet control, manual disimpaction, and enemas. Most patients with NTDs can be continent of stool with these measures.
The ability to ambulate is influenced by the level of the neural lesion, hydrocephalus, pelvic anatomy, limb deformities, tethered cord, scoliosis, kyphosis, and syringomyelia, and varying degrees of ambulation exist. Strong hip flexors, adductors, and quadriceps are required to be ambulatory. Some children can ambulate in the community, some only in the home, others can only stand but not walk, and the rest are wheelchair bound. However, many children with NTDs, such as lumbar myelomeningocele, lose their ability to ambulate as they get older. In general, patients with a sacral lesion can ambulate, those with a thoracic lesion cannot.
Steinbok noted that about 60% of children with NTDs attended normal classes, while 40% were in special classes or operated below their grade level. Approximately 10-40% of children with myelomeningocele are probably employable at some level, depending on the patient's intellectual abilities, ambulation status, and environmental influences.
Over the past 2 decades, allergy to latex has been recognized in an increasing number of children with myelomeningocele. Up to 50% of children with myelomeningocele may be latex sensitive. This appears to be a result of a massive immunoglobulin E (IgE) response to the antigen in latex that is derived from the Heva brasiliensis plant. Most patients with myelomeningocele should be treated with latex precautions when undergoing surgery. Surgeons and health care providers should work with latex-free gloves and plastics so that they can avoid latex-induced anaphylaxis, which can be life threatening. Medications such as corticosteroids, Benadryl, bronchodilators, and epinephrine should be available as a precaution during surgery on these children.
Neurosurgeons need to be wary of late-life neurologic deterioration in children and adults. The most common deterioration seen is from a tethered spinal cord. A routine MRI reveals a spinal cord that ends in the lumbar or sacral regions in almost all patients with myelomeningocele (seeImage 3). This is normal in many patients without any new neurologic complaints. Despite careful surgical closure of the original neural placode, approximately 20% or more of all patients with myelomeningocele require an untethering of their spinal cord later in their life. They may present with gait difficulty, back pain, leg weakness, sensory loss, a new foot deformity, or simply a change in their urodynamic data or urinary continence. These patients require a surgical exploration to free the neural placode and nerve roots from the dorsal surface of their dura. Patients with tethered cords on MRI but no new complaints do not require reexploration.
Diastematomyelia can be diagnosed using MRI or CT/myelogram. An enlarging syringomyelia can be the result of a symptomatic CM II or retethering of the spinal cord. Many functional deteriorations result from progressive orthopedic deformities such as scoliosis, pelvic obliquity, and limb deformities. An orthopedic surgeon well versed in the care of patients with NTDs is required to execute a reasonable plan to repair or stabilize treatable disorders.
In general, a multidisciplinary team consisting of neonatologist, pediatrician, pediatric neurosurgeon, pediatric urologist, pediatric orthopedic surgeon, physical therapist, nurse, nutritionist, psychologist, and teacher are required to direct the care of children with NTDs.
For more information on spina bifida and related conditions, I would highly recommend a visit to emedicine.com.
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