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Spina Bifida 

Definition

Spina bifida is a serious birth abnormality in which the spinal cord is malformed and lacks its usual protective skeletal and soft tissue coverings.

Description

Spina bifida may appear in the body midline anywhere from the neck to the buttocks. In its most severe form, termed spinal rachischisis, the entire spinal canal is open, exposing the spinal cord and nerves. More commonly, the abnormality appears as a localized mass on the back that is covered by skin or by the meninges, the three-layered membrane that envelopes the spina cord. Spina bifida is usually readily apparent at birth because of the malformation of the back and paralysis below the level of the abnormality.

Various forms of spina bifida are known as meningomyelocele, myelomeningocele, spina bifida aperta, open spina bifida, myelodysplasia, spinal dysraphism, spinal rachischisis, myelocele, and meningocele. The term meningocele is used when the spine malformation contains only the protective covering (meninges) of the spinal cord. The other terms indicate involvement of the spinal cord and nerves in the malformation. A related term, spina bifida occulta, indicates that one or more of the bony bodies in the spine are incompletely hardened, but that there is no abnormality of the spinal cord itself.

Spina bifida occurs worldwide, but there has been a steady downward trend in occurrence rates over the past 50-70 years, particularly in regions of high prevalence. The highest prevalence rates, about one in 200 pregnancies, have been reported from certain northern provinces in China. Intermediate prevalence rates, about one in 1,000 pregnancies, have been found in Central and South America. The lowest prevalence rates, less than one in 2,000 pregnancies, have been found in the European countries. The highest regional prevalence in the United States of about one in 500 pregnancies has occurred in the Southeast.

Causes and symptoms

Spina bifida may occur as an isolated abnormality or in the company of other malformations. As an isolated abnormality, spina bifida is caused by the combination of genetic factors and environmental influences that bring about malformation of the spine and spinal column. The specific genes and environmental influences that contribute to the many-factored causes of spina bifida are not completely known. An insufficiency of folic acid is known to be one influential nutritional factor. Changes (mutations) in genes involving the metabolism of folic acid are believed to be significant genetic risk factors. The recurrence risk after the birth of an infant with isolated spina bifida is 3-5%. Recurrence may be for spina bifida or another type of spinal abnormality.

Spina bifida may arise because of chromosome abnormalities, single gene mutations, or specific environmental insults such as maternal diabetes mellitus or prenatal exposure to certain anticonvulsant drugs. The recurrence risk varies with each of these specific causes.

In most cases, spina bifida is obvious at birth because of malformation of the spine. The spine may be completely open, exposing the spinal cord and nerves. More commonly, the spine abnormality appears as a mass on the back covered by membrane (meninges) or skin. Spina bifida may occur anywhere from the base of the skull to the buttocks. About 75% of abnormalities occur in the lower back (lumbar) region. In rare instances, the spinal cord malformation may occur internally, sometimes with a connection to the gastrointestinal tract.

In spina bifida, many complications arise, dependent in part on the level and severity of the spine malformation. As a rule, the nerves below the level of the abnormality develop in a faulty manner and fail to function, resulting in paralysis and loss of sensation below the level of the spine malformation. Since most abnormalities occur in the lumbar region, the lower limbs are paralyzed and lack sensation. Furthermore, the bowel and bladder have inadequate nerve connections, causing an inability to control bowel and bladder function. Most infants also develop hydrocephaly, an accumulation of excess fluid in the four cavities of the brain. At least one of every seven cases develop findings of Chiari II malformation, a condition in which the lower part of the brain is crowded and may be forced into the upper part of the spinal cavity.

There are a number of mild variant forms of spina bifida, including multiple vertebral abnormalities, skin dimples, tufts of hair, and localized areas of skin deficiency over the spine. Two variants, lipomeningocele and lipomyelomeningocele, typically occur in the lower back area (lumbar or sacral) of the spine. In these conditions, a tumor of fatty tissue becomes isolated among the nerves below the spinal cord, which may result in tethering of the spinal cord and complications similar to those with open spina bifida.

Diagnosis

Few disorders are to be confused with open spina bifida. The diagnosis is usually obvious based on the external findings at birth. Paralysis below the level of the abnormality and fluid on the brain (hydrocephaly) may contribute to the diagnosis. Other spine abnormalities such as congenital scoliosis and kyphosis, or soft tissue tumors overlying the spine, are not likely to have these accompanying findings. In cases in which there are no external findings, the diagnosis is more difficult and may not become evident until neurological abnormalities or hydrocephaly develop weeks, months, or years following birth.

Prenatal diagnosis may be made in most cases with ultrasound examination after 12-14 weeks of pregnancy. Many cases are also detected by the testing of the mother's blood for the level of alpha-fetoprotein at about 16 weeks of pregnancy. If the spine malformation is not skin covered, alpha-fetoprotein from the fetus' circulation may leak into the surrounding amniotic fluid, a small portion of which is absorbed into the mother's blood.

Treatment

Aggressive surgical and medical management have improved the survival and function of infants with spina bifida. Initial surgery may be carried out during the first days of life, providing protection against injury and infection. Subsequent surgery is often necessary to protect against excessive curvature of the spine, and in the presence of hydrocephaly, to place a mechanical shunt to decrease the pressure and amount of cerebrospinal fluid in the cavities of the brain. Because of weakness or paralysis below the level of the spine abnormality, most children will require physical therapy, bracing, and other orthopedic assistance to enable them to walk. A variety of approaches including periodic bladder catheterization, surgical diversion of urine, and antibiotics are used to protect urinary function.

Although most individuals with spina bifida have normal intellectual function, learning disabilities or mental retardation occur in a minority. This may result, in part, from hydrocephaly and/or infections of the nervous system. Children so affected may benefit from early educational intervention, physical therapy, and occupational therapy. Counseling to improve self-image and lessen barriers to socialization becomes important in late childhood and adolescence.

Open fetal surgery has been performed for spina bifida during the last half of pregnancy. After direct closure of the spine malformation, the fetus is returned to the womb. By preventing chronic intrauterine exposure to mechanical and chemical trauma, prenatal surgery improves neurological function and leads to fewer complications after birth. Fetal surgery is considered experimental, and results have been mixed.

Key terms

Chiari II anomaly — A structural abnormality of the lower portion of the brain (cerebellum and brain stem) associated with spina bifida. The lower structures of the brain are crowded and may be forced into the foramen magnum, the opening through which the brain and spinal cord are connected.

Fetus — The term used to describe a developing human infant from approximately the third month of pregnancy until delivery. The term embryo is used prior to the third month.

Hydrocephalus — The excess accumulation of cerebrospinal fluid around the brain, often causing enlargement of the head.

Prevention of isolated spina bifida and other spinal abnormalities has become possible during recent decades. The major prevention is through the use of a B vitamin, folic acid, for several months prior to and following conception. The Centers for Disease Control and Prevention recommend the intake of 400 micrograms of synthetic folic acid every day for all women of childbearing years.

Prognosis

More than 80% of infants born with spina bifida survive with surgical and medical management. Although complications from paralysis, hydrocephaly, Chiari II malformation, and urinary tract deterioration threaten the well-being of the survivors, the outlook for normal intellectual function is good.

Resources

Organizations

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Ave., White Plains, NY 10605. (888) 663-4637. http://www.modimes.org.

National Birth Defects Prevention Network. Atlanta, GA (770) 488-3550. http://www.nbdpn.org.

Shriners Hospitals for Children. International Shrine Headquarters, 2900 Rocky Point Dr., Tampa, FL 33607-1460. (813) 281-0300. http://www.shrinershq.org.

Spina Bifida Association of America. 4590 MacArthur Blvd. NW, Suite 250, Washington, DC 20007-4226. (800) 621-3141 or (202) 944-3285. Fax: (202) 944-3295.

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spina /spi·na/ (spi´nah) pl. spi´nae   [L.] spine.

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spina bi´fida  a developmental anomaly marked by defective closure of the vertebral arch, through which the meninges may (s. bi´fida cys´tica) or may not (s. bi´fida occul´ta) protrude.

Two types of spina bifida cystica shown in transverse section through the spinal column. (A), Meningocele, characterized by protrusion of the meninges; (B), a form of myelocele characterized by myeloschisis and protrusion of the defective spinal cord.

Spina bifida occulta shown in a transverse section through the spinal column.

spina vento´sa  dactylitis, usually in infants and young children, with enlargement of digits, caseation, sequestration, and sinus formation.

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spina bif·i·da (bf-d) n. A congenital defect in which the spinal column is imperfectly closed so that part of the meninges or spinal cord may protrude, often resulting in neurological disorders. Also called hydrocele spinalis.

spina bifida Top: normal spinal cord Center: myelomeningocele spina bifida Bottom: showing the protrusion

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spina bifida

[bif′ədə, bī′fədə]

a congenital neural tube defect in which there is a developmental anomaly in the posterior vertebral arch. Spina bifida is relatively common, occurring approximately 10 to 20 times per 1000 births. It may occur with only a small deformed lamina separated by a midline gap, or it may be associated with the complete absence of laminae surrounding a large area. In cases where the separation is wide enough, contents of the spinal canal protrude posteriorly and a myelomeningocele is evident. Neurologic deficits do not usually accompany the anomalies involving only bony deformity. Direct signs and symptoms are rarely noted in spina bifida, which is frequently diagnosed accidentally during radiographic examinations required for other reasons. Spina bifida that does not involve herniation of the meninges or the contents of the spinal canal (spina bifida occulta) rarely requires treatment. Also called spinal dysrhaphism.

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spina bifida (spīˑ·n biˑ·fi·d),

n a congenital defect of the neural tube marked by absence of vertebral arches, through which the spinal cord and membranes may protrude; symptoms are few unless several vertebrae are affected. Also called
spinal dysrhaphia.

Spina bifida.

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spina bifida,

n a congenital neural tube defect characterized by a developmental anomaly in the posterior vertebral arch. It is relatively common.

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spina

pl. spinae [L.] spine; a slender process such as occurs on many bones.

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spina bifida

a developmental anomaly characterized by defective closure of the two halves of the vertebral arch through which the spinal cord and meninges may or may not protrude.

spina bifida cystica

spina bifida in which there is protrusion through the defect of a cystic swelling involving the meninges (meningocele), spinal cord (myelocele) or both (meningomyelocele).

spina bifida occulta

spina bifida in which there is a defect of the bony spinal canal without protrusion of the cord or meninges.

spina bifida ventralis

a defect of closure on the ventral surface of the bony spinal canal, often associated with defective development of the abdominal and thoracic viscera.

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spina bifida

Neurology A group of birth defects caused by a defective fusion of the vertebral arch and one or more contiguous vertebrae, leaving a variably sized opening in the spinal canal; in SB, the spinal meninges and subcutaneous tissue may herniate through the defect, but remain covered by skin and subcutaneous tissue; protrusion of the spinal cord and meninges damages the spinal cord and nerve roots, compromising function at or below the defect Clinical Related to anatomic level of defect, usually in the lower lumbar or sacral region–partial or complete paralysis of legs, partial or complete lack of sensation, loss of bladder or bowel control; exposed spinal cord is susceptible to infection–meningitis Concomitant congenital defects Hydrocephalus–in 90% of children with myelomeningocele, syringomyelia, hip dislocation Lab ↑ AFP; occult SB affects up to 10% of adults seen in 3º care centers. See Alpha-fetoprotein, Multivitamins, Myelomeningocele.