Spina bifida

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Spina bifida
Classification and external resources
ICD-10Q05, Q76.0
ICD-9741, 756.17
OMIM182940
DiseasesDB12306
eMedicineorthoped/557
MeSHC10.500.680.800
 
  (Redirected from Myelomeningocele)
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Spina bifida
Classification and external resources
ICD-10Q05, Q76.0
ICD-9741, 756.17
OMIM182940
DiseasesDB12306
eMedicineorthoped/557
MeSHC10.500.680.800

Spina bifida (Latin: "split spine") is a developmental congenital disorder caused by the incomplete closing of the embryonic neural tube. Some vertebrae overlying the spinal cord are not fully formed and remain unfused and open. If the opening is large enough, this allows a portion of the spinal cord to protrude through the opening in the bones. There may or may not be a fluid-filled sac surrounding the spinal cord. Other neural tube defects include anencephaly, a condition in which the portion of the neural tube that will become the cerebrum does not close, and encephalocele, which results when other parts of the brain remain unfused.

Spina bifida malformations fall into three categories: spina bifida occulta, spina bifida cystica with meningocele, and spina bifida cystica with myelomeningocele. The most common location of the malformations is the lumbar and sacral areas. Myelomeningocele is the most significant and common form, and this leads to disability in most affected individuals. The terms spina bifida and myelomeningocele are usually used interchangeably.

Spina bifida can be surgically closed after birth, but this does not restore normal function to the affected part of the spinal cord. Intrauterine surgery for spina bifida has also been performed, and the safety and efficacy of this procedure is currently being investigated. The incidence of spina bifida can be decreased by up to 70% when daily folic acid supplements are taken prior to conception.

Contents

Classification

X-ray image of spina bifida occulta in S-1
Unfused arch of C1 at CT
Myelomeningocele in the lumbar area
(1) External sac with cerebrospinal fluid
(2) Spinal cord wedged between the vertebrae

Spina bifida occulta

Occulta is Latin for "hidden". This is the mildest form of spina bifida.[1]

In occulta, the outer part of some of the vertebrae are not completely closed.[2] The splits in the vertebrae are so small, the spinal cord does not protrude. The skin at the site of the lesion may be normal, or it may have some hair growing from it; there may be a dimple in the skin, or a birthmark.[3]

Many people with this type of spina bifida do not even know they have it, as the condition is asymptomatic in most cases.[3] The incidence of spina bifida occulta is approximately 10% of the population,[4] and most people are diagnosed incidentally from spinal X-rays. A systematic review of radiographic research studies found no relationship between spina bifida occulta and back pain.[5] More recent studies not included in the review support the negative findings.[6][7][8]

However, other studies suggest spina bifida occulta is not always harmless. One study found, among patients with back pain, severity is worse if spina bifida occulta is present.[9][10]

Meningocele

The least common form of spina bifida is a posterior meningocele (or meningeal cyst). In this form, the vertebrae develop normally, but the meninges are forced into the gaps between the vertebrae. As the nervous system remains undamaged, individuals with meningocele are unlikely to suffer long-term health problems, although cases of tethered cord have been reported. Causes of meningocele include teratoma and other tumors of the sacrococcyx and of the presacral space, and Currarino syndrome.

A meningocele may also form through dehiscences in the base of skull. These may be classified by their localisation to occipital, frontoethmoidal, or nasal. Endonasal meningoceles lie at the roof of the nasal cavity and may be mistaken for a nasal polyp. They are treated surgically. Encephalomeningoceles are classified in the same way and also contain brain tissue.

Myelomeningocele

This type of spina bifida is the most common and often results in the most severe complications.[11] In individuals with myelomeningocele, the unfused portion of the spinal column allows the spinal cord to protrude through an opening. The meningeal membranes that cover the spinal cord form a sac enclosing the spinal elements. Spina bifida with myeloschisis is the most severe form of myelomeningocele. In this type, the involved area is represented by a flattened, plate-like mass of nervous tissue with no overlying membrane. The exposure of these nerves and tissues make the baby more prone to life-threatening infections such as meningitis.[12][not specific enough to verify]

The protruded portion of the spinal cord and the nerves that originate at that level of the cord are damaged or not properly developed. As a result, there is usually some degree of paralysis and loss of sensation below the level of the spinal cord defect. Thus, the more cranial the level of the defect, the more severe the associated nerve dysfunction and resultant paralysis may be. People may have ambulatory problems, loss of sensation, deformities of the hips, knees or feet, and loss of muscle tone.

Signs and symptoms

Physical complications

Physical signs of spina bifida may include:

According to the Spina Bifida Association of America (SBAA), over 73% of people with spina bifida develop an allergy to latex[citation needed], ranging from mild to life-threatening. The common use of latex in medical facilities makes this a particularly serious concern. The most common approach to avoid developing an allergy is to avoid contact with latex-containing products such as examination gloves, condoms, catheters, and many of the products used by dentists.[2]

The spinal cord lesion or the scarring due to surgery may result in a tethered spinal cord. In some individuals, this causes significant traction and stress on the spinal cord and can lead to a worsening of associated paralysis, scoliosis, back pain, and worsening bowel and/or bladder function.[15]

Neurological complications

Many individuals with spina bifida will have an associated abnormality of the cerebellum, called the Arnold Chiari II malformation. In affected individuals, the back portion of the brain is displaced from the back of the skull down into the upper neck. In about 90% of the people with myelomeningocele, hydrocephalus will also occur because the displaced cerebellum interferes with the normal flow of cerebrospinal fluid, causing an excess of the fluid to accumulate.[16] In fact, the cerebellum also tends to be smaller in individuals with spina bifida, especially for those with higher lesion levels.[14]

The corpus callosum is abnormally developed in 70-90% of individuals with spina bifida myelomeningocele; this impacts the communication processes between the left and right brain hemispheres.[17] Further, white matter tracts connecting posterior brain regions with anterior regions appear less organized. White matter tracts between frontal regions have also been found to be impaired.[14]

Cortex abnormalities may also be present. For example, frontal regions of the brain tend to be thicker than expected, while posterior and parietal regions are thinner. Thinner sections of the brain are also associated with increased cortical folding.[14] Neurons within the cortex may also be displaced.[18]

Executive function

Several studies have demonstrated difficulties with executive functions in youth with spina bifida,[19][20] with greater deficits observed in youth with shunted hydrocephalus.[21] Unlike typically developing children, youth with spina bifida do not tend to improve in their executive functioning as they grow older.[20] Specific areas of difficulty in some individuals include planning, organizing, initiating, and working memory. Problem-solving, abstraction, and visual planning may also be impaired.[22] Further, children with spina bifida may have poor cognitive flexibility. Although executive functions are often attributed to the frontal lobes of the brain, individuals with spina bifida have intact frontal lobes; therefore, other areas of the brain may be implicated.[21]

Individuals with spina bifida, especially those with shunted hydrocephalus, often have attention problems. Children with spina bifida and shunted hydrocephalus have higher rates of ADHD than typically developing children (31% vs. 17%).[19] Deficits have been observed for selective attention and focused attention, although poor motor speed may contribute to poor scores on tests of attention.[21][23] Attention deficits may be evident at a very early age, as infants with spina bifida lag behind their peers in orienting to faces.[24]

Academic skills

Individuals with spina bifida may struggle academically, especially in the subjects of mathematics and reading. In one study, 60% of children with spina bifida were diagnosed with a learning disability.[25] In addition to brain abnormalities directly related to various academic skills, achievement is likely affected by impaired attentional control and executive functioning.[18] Children with spina bifida may perform well in elementary school, but begin to struggle as academic demands increase.

Children with spina bifida are more likely than their typically developing peers to have dyscalculia.[26] Individuals with spina bifida have demonstrated stable difficulties with arithmetic accuracy and speed, mathematical problem-solving, and general use and understanding of numbers in everyday life.[27] Mathematics difficulties may be directly related to the thinning of the parietal lobes (regions implicated in mathematical functioning) and indirectly associated with deformities of the cerebellum and midbrain that affect other functions involved in mathematical skills. Further, higher numbers of shunt revisions are associated with poorer mathematics abilities.[28] Working memory and inhibitory control deficiencies have been implicated for math difficulties,[29] although visual-spatial difficulties are not likely involved.[26] Early intervention to address mathematics difficulties and associated executive functions is crucial.[29]

Individuals with spina bifida tend to have better reading skills than mathematics skills.[28] Children and adults with spina bifida have stronger abilities in reading accuracy compared to reading comprehension.[30] Comprehension may be especially impaired for text that requires an abstract synthesis of information rather than a more literal understanding.[31] Individuals with spina bifida may have difficulty with writing due to deficits in fine motor control and working memory.[30]

Social complications

Compared to typically developing children, youth with spina bifida may have fewer friends[32] and spend less time with peers.[33] They may be more socially immature and more passive in social situations.[33] These children have also reported feeling less close to their friends and feel they do not receive as much emotional support from their friendships.[34] Many social difficulties tend to be stable, lasting into adulthood.[35] Youth encountering the most social difficulties tend to have lower executive functioning[36] and shunted hydrocephalus.[37] However, not all studies have found social difficulties in these youth compared with their typically developing peers.[38]

Pathophysiology

Spina bifida is caused by the failure of the neural tube to close during the first month of embryonic development (often before the mother knows she is pregnant).

Under normal circumstances, the closure of the neural tube occurs around the 23rd (rostral closure) and 27th (caudal closure) day after fertilization.[39] However, if something interferes and the tube fails to close properly, a neural tube defect will occur. Medications such as some anticonvulsants, diabetes, having a relative with spina bifida, obesity, and an increased body temperature from fever or external sources such as hot tubs and electric blankets may increase the chances of delivery of a baby with a spina bifida.

Extensive evidence from mouse strains with spina bifida indicates sometimes a genetic basis for the condition. In human spina bifida, as with other human diseases, such as cancer, hypertension and atherosclerosis (coronary artery disease), spina bifida likely results from the interaction of multiple genes and environmental factors.

Research has shown the lack of folic acid (folate) is a contributing factor in the pathogenesis of neural tube defects, including spina bifida. Supplementation of the mother's diet with folate can reduce the incidence of neural tube defects by about 70%, and can also decrease the severity of these defects when they occur.[40][41][42] It is unknown how or why folic acid has this effect.

Spina bifida does not follow direct patterns of heredity like muscular dystrophy or haemophilia. Studies show a woman having had one child with a neural tube defect such as spina bifida has about a 3% risk of having another child with a neural tube defect. This risk can be reduced to about 1% if the woman takes high doses (4 mg/day) of folic acid before and during pregnancy. For the general population, low-dose folic acid supplements are advised (0.4 mg/day).[citation needed]

Prevention

Three-dimensional ultrasound image of the fetal spine at 21 weeks of pregnancy

There is neither a single cause of spina bifida nor any known way to prevent it entirely. However, dietary supplementation with folic acid has been shown to be helpful in reducing the incidence of spina bifida. Sources of folic acid include whole grains, fortified breakfast cereals, dried beans, leaf vegetables and fruits.[43]

Folate fortification of enriched grain products has been mandatory in the United States since 1998. The U.S. Food and Drug Administration, Public Health Agency of Canada[44] and UK recommended amount of folic acid for women of childbearing age and women planning to become pregnant is at least 0.4 mg/day of folic acid from at least three months before conception, and continued for the first 12 weeks of pregnancy.[45] Women who have already had a baby with spina bifida or other type of neural tube defect, or are taking anticonvulsant medication should take a higher dose of 4–5 mg/day.[45]

Certain mutations in the gene VANGL1 are implicated as a risk factor for spina bifida: These mutations have been linked with spina bifida in some families with a history of spina bifida.[46]

Pregnancy screening

Neural tube defects can usually be detected during pregnancy by testing the mother's blood (AFP screening) or a detailed fetal ultrasound. Increased levels of maternal serum alpha-fetoprotein (MSAFP) should be followed up by two tests - an ultrasound of the fetal spine and amniocentesis of the mother's amniotic fluid (to test for alpha-fetoprotein and acetylcholinesterase). Spina bifida may be associated with other malformations as in dysmorphic syndromes, often resulting in spontaneous miscarriage. In the majority of cases, though, spina bifida is an isolated malformation.

Genetic counseling and further genetic testing, such as amniocentesis, may be offered during the pregnancy, as some neural tube defects are associated with genetic disorders such as trisomy 18. Ultrasound screening for spina bifida is partly responsible for the decline in new cases, because many pregnancies are terminated out of fear that a newborn might have a poor future quality of life. With modern medical care, the quality of life of patients has greatly improved.[39]

Spina bifida lombare sagittale.theora.ogv
Ultrasound view of the fetal spine at 21 weeks of pregnancy. In the longitudinal scan a lumbar myelomeningocele is seen.

Treatment

There is no known cure for nerve damage caused by spina bifida. To prevent further damage of the nervous tissue and to prevent infection, pediatric neurosurgeons operate to close the opening on the back. The spinal cord and its nerve roots are put back inside the spine and covered with meninges. In addition, a shunt may be surgically installed to provide a continuous drain for the excess cerebrospinal fluid produced in the brain, as happens with hydrocephalus. Shunts most commonly drain into the abdomen or chest wall. However, if spina bifida is detected during pregnancy, then open fetal surgery can be performed.[16]

In childhood

Most individuals with myelomeningocele will need periodic evaluations by a variety of specialists:[47]

Transition to adulthood

Although many children's hospitals feature integrated multidisciplinary teams to coordinate healthcare of youth with spina bifida, the transition to adult healthcare can be difficult because the above healthcare professionals operate independently of each other, requiring separate appointments and communicate among each other much less frequently. Healthcare professionals working with adults may also be less knowledgeable about spina bifida because it is considered a childhood chronic health condition.[48] Due to the potential difficulties of the transition, adolescents with spina bifida and their families are encouraged to begin to prepare for the transition around ages 14–16, although this may vary depending on the adolescent's cognitive and physical abilities and available family support. The transition itself should be gradual and flexible. The adolescent's multidisciplinary treatment team may aid in the process by preparing comprehensive, up-to-date documents detailing the adolescent's medical care, including information about medications, surgery, therapies, and recommendations. A transition plan and aid in identifying adult healthcare professionals are also helpful to include in the transition process.[48]

Further complicating the transition process is the tendency for youth with spina bifida to be delayed in the development of autonomy,[49] with boys particularly at risk for slower development of independence.[50] An increased dependence on others (in particular family members) may interfere with the adolescent's self-management of health-related tasks, such as catheterization, bowel management, and taking medications.[51] As part of the transition process, it is beneficial to begin discussions at an early age about educational and vocational goals, independent living, and community involvement.[52]

Epidemiology

Spina bifida is one of the most common birth defects, with an average worldwide incidence of one to two cases per 1000 births, but certain populations have a significantly greater risk.

In the United States, the average incidence is 0.7 per 1000 live births. The incidence is higher on the East Coast than on the West Coast, and higher in whites (one case per 1000 live births) than in blacks (0.1–0.4 case per 1000 live births). Immigrants from Ireland have a higher incidence of spina bifida than do natives.[53][54] Highest rates of the defect in the USA can be found in Hispanic youth.[55]

The highest incidence rates worldwide were found in Ireland and Wales, where three to four cases of myelomeningocele per 1000 population have been reported during the 1970s, along with more than six cases of anencephaly (both live births and stillbirths) per 1000 population. The reported overall incidence of myelomeningocele in the British Isles was 2.0–3.5 cases per 1000 births.[53][54] Since then, the rate has fallen dramatically with 0.15 per 1000 live births reported in 1998,[39] though this decline is partially accounted for because some fetuses are aborted when tests show signs of spina bifida (see Pregnancy screening above).

Parents of children with spina bifida have an increased risk of having a second child with a neural tube defect.[53][54]

This condition is more likely to appear in females; the cause for this is unknown.[citation needed]

Fetal Surgery Research

1980 - Fetal surgical techniques using animal models were first developed at the University of California, San Francisco by Dr. Michael R. Harrison, Dr. N. Scott Adzick and research colleagues.

1994 - The surgical model that is most similar to simulating the human disease is the fetal lamb model of myelomeningocele (MMC) introduced by Meuli and Adzick in 1994. The MMC-like defect was surgically created at 75 days of gestation (term 145 to 150 days) by a lumbo-sacral laminectomy. Approximately 3 weeks after creation of the defect a reversed latissimus dorsi flap was used to cover the exposed neural placode and the animals were delivered by cesarean section just prior term. Human MMC-like lesions with similar neurological deficit were found in the control newborn lambs. In contrast, animals that underwent closure had near-normal neurological function and well-preserved cytoarchitecture of the covered spinal cord on histopathological examination. Despite mild paraparesis, they were able to stand, walk, perform demanding motor test and demonstrated no signs of incontinence. Furthermore, sensory function of the hind limbs was present clinically and confirmed electrophysiologically. Further studies.showed that this model when combined with a lumbar spinal cord myelotomy leads to the hindbrain herniation characteristic of the Chiari II malformation and that in utero surgery restores normal hindbrain anatomy by stopping the leak of cerebrospinal fluid through the myelomeningocele lesion.[56][57][58][59]

Surgeons at Vanderbilt University, led by Dr. Joseph Bruner, attempted to close spina bifida in 4 human fetuses using a skin graft from the mother using specialized telescope called a laparoscope. Four cases were performed before stopping the procedure - two of the four fetuses died. [60]

1998 - Dr. N. Scott Adzick and team at The Children’s Hospital of Philadelphia performed open fetal surgery for spina bifida in an early gestation fetus (22 week gestation fetus) with a successful outcome. [61]

Surgeons at Vanderbilt University, led by Dr. Noel Tulipan, made an incision in the mother's uterus to obtain better exposure to fetuses of 28 to 30 weeks gestation. All 4 fetuses were born premature but with evidence of reversal of their chiari II malformation. Only 2 of the 4 required ventricular shunts after birth. Fetal surgery after 25 weeks has not shown benefit in subsequent studies. [62]

Subsequently, 4 medical centers conducted 253 open spina bifida repairs prior to the MOMs trial. The outcomes were mixed and the only comparison groups were other children that had not undergone repair after birth in the past.

Management of Myelomeningocele Study (MOMS)[63][64] is a phase III clinical trial to evaluate the safety and efficacy of fetal surgery to close a myelomeningocele. This involves surgically opening the pregnant mother's abdomen and uterus to operate on the fetus. This route of access to the fetus is called "open fetal surgery". The exposed fetal spinal cord is covered in layers with surrounding fetal tissue at mid-gestation (19-25 weeks) to protect it from further damage caused by prolonged exposure to amniotic fluid. The fetal surgery may decrease some of the damaging effects of the spina bifida, but at some risk to both the fetus and the pregnant woman.

The MOMS trial was closed for efficacy in December 2010 based on comparing outcomes after prenatal and postnatal repair in 183 patients - 77 patients were treated at The Children’s Hospital of Philadelphia, 54 at Vanderbilt University and 52 at The University of California San Francisco.

The trial demonstrated the outcomes after prenatal spina bifida treatment are improved to the degree that the benefits of the surgery outweigh the maternal risks. Results were reported in the New England Journal of Medicine by Adzick et al.[65]

To be specific, the study found that prenatal repair resulted in:

In contrast to the open fetal operative approach tested in the MOMS, a minimally invasive approach is currently being tested by the German Center for Fetal Surgery and Minimally Invasive Therapy at the University of Giessen, Germany.[66] This approach uses three small tubes (trocars) with an external diameter of 5 mm that are directly placed via small needle punctures through the maternal abdominal wall into the uterine cavity. Via this route, the unborn can be postured and its spina bifida defect be closed using small instruments. In contrast to open fetal surgery, the fetoscopic approach results in less trauma to the mother, as large incisions of her abdomen and uterus are not required. Early results indicate the approach may maintain the fetal muscular and sensory function still present at the time of fetal surgery, regardless of lesion height.

Although fetoscopic techniques that involve making multiple puncture wounds in the uterus are theoretically appealing to potentially mitigate maternal morbidity, clinical reports on their use are limited and the results have been disappointing, primarily because of uterine membrane problems leading to premature birth three to six weeks after the procedure and delivery before 30 weeks of gestation.[67] As compared with the open fetal surgery technique, fetoscopic repair of myelomeningocele has resulted in higher rates of fetal death, premature rupture of membranes, chorioamnionitis, oligohydramnios, premature delivery, and persistent hindbrain herniation.[68][69][70] If the problems of membrane rupture associated with fetoscopy can be solved, this minimally invasive approach to repairing myelomeningocele before birth should be tested clinically.

Notable people

Notable people with spina bifida include:

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