Spina bifida is a neural tube defect that leads to a congenital defect in the posterior bony wall of the spinal canal [vertebral arch] involving the laminae and spinal cord malformation that occurs in varying degrees of severity and range of presentation from an incidental finding on x-ray to stillbirth.
Spina bifida is most commonly seen in the lumbosacral region. Sometimes the contents of the canal may protrude through the defect.
The average worldwide incidence of spina bifida is 1 case per 1000 births, but marked geographic variations occur.
The term bifida is derived from the Latin bifidus which means “in 2 parts.”
Development of the spinal cord
During the 2nd week of intrauterine life, a dorsal groove appears on the surface of the embryo, which is known as the neural groove. The margins of the neural groove unite into a tube known as the neural tube and the lumen, within it, is called the neural canal.
The neural tube becomes separated from the surface by an ingrowth of the mesoderm.
In front of the neural tube, there is a solid rod of cells, known as the notochord. Around the notochord, the vertebral bodies develop.
From each of the bodies, there extend two projections which grow around the neural tube to form the vertebral arch or neural arch.
Failure of fusion of these arches gives rise to spina bifida.
Neural tube defects result from failed closure and abnormal differentiation of the embryonic neural tube. These occur between the 17th and 30th day of gestation.
Anencephaly and myelomeningocele are the most common neural tube defects.
Myelomeningocele occurs due to a failed closure of the caudal end of the neural tube resulting in a sac which contains dysplastic spinal cord, nerve roots, meninges, vertebral bodies, and skin.
The etiology in most cases of spina bifida is multifactorial.
Most infants born with spina bifida are born to mothers with no previously affected children
Up to 10% of fetuses with a neural tube defect detected in early gestation have an associated chromosome abnormality.
Maternal risk factors
- Folic acid deficiency [about 50% of cases are attributed]
- Pregestational diabetes – increases the risk of CNS malformation
- Maternal obesity
- Maternal diarrhea
- Intrauterine exposure to antiepileptic drugs and drugs used to induce ovulation
- Maternal exposures to
- Fumonisins [toxins produced by fungi]
- Electromagnetic fields
- Hazardous waste sites
- Disinfection by-products found in drinking water
Note on the tethered cord
A fibrous band, the membrana reunions connects the skin to the spinal theca.
At one stage the spinal cord reaches the distal end of the vertebral column. Gradually the cord lags behind in growth in comparison to the vertebral column in intrauterine life so that at birth the distal end of the cord lies at the third lumbar vertebra.
Later on, due to more development of the vertebral column, the distal end of the cord lies at the lower end of the first lumbar vertebra in adults. With the growth of the body, the membrana reunions pull on the theca and nerve roots. This causes some neurological deficiencies e.g. foot drop, nocturnal enuresis or a backache. Such symptoms appear late in childhood or in adult life.
Types of Spina bifida
Spina Bifida Occulta
In Spina Bifida Occulta, though there is a failure of the neural arches to unite, and a small gap exists in one of the vertebral arches, usually in the lumbar or sacral regions. There is no protrusion of the cord or membranes. Frequently only one vertebra is affected and the gap is filled with fibrous tissue.
Subtle signs of underlying abnormality in bifida occulta are dimple, skin pigmentation or hairy patch. Otherwise, spina bifida occulta is almost always without consequences.
A spinal cord lipoma or a fibrous cord may be present underneath these subtle signs.
Problems with micturition or a foot deformity may be seen in some cases of occulta.
In later ages, the patient may present with tethered cord.
Many cases of spinal bifida occulta are symptomless. Either they remain undiagnosed or diagnosed by accident when an x-ray taken for some other reasons.
- Present since birth
- There is some abnormality in the local skin either a skin dimple or a local patch of hair or a naevo-lipoma or simple lipoma.
- Neurological examinations must be performed, as in adolescent or in adult life manifestations of such deficiency may be revealed in the form of a backache, nocturnal enuresis, local anesthesia, local paresis or even foot drop.
- X-ray is often confirmatory as it will show the bony defect.
- Presence of tuft of hair or lipoma may lead to a cosmetic complaint and this is treated by excision of these lesions.
- If there are neurological symptoms due to membrana reunions, [tethered cord syndrome] the membrana reunions is excised in its whole length from the skin through the vertebral gap to the spinal meninges.
- Extradural or intradural lipomas causing compression of neural tissue should be excised.
Spina bifida cystica
In this type, the spine is bifid and a cyst forms. Meningocele actually refers to a cystic swelling of the dura and arachnoid which protrudes through the spina bifida defect in the vertebral arch. A person with a meningocele may have no neurologic sequelae.
When cord tissue extends into the meningocele, it is called a myelomeningocele. Meningomyelocele is a form of spina bifida cystica is the most common type of spina bifida, accounting for 94% of cases. [Spina bifida occulta not included in this figure]
The most severe type of spina bifida cystica is the myelocele [also called myeloschisis] where the open neural plate has spread out onto the surface and is covered just by epithelium.
In this condition protrusion of meninges occurs through the defect in the neural arch. Such protrusion contains only cerebrospinal fluid. So it gives rise to a cystic swelling.
Usually the duramater stops at the margin of the defect and usually the pia and arachnoid protrude. The overlying skin remains intact.
It is common in the lumbosacral region. Meningocele also occurs in the skull, where it is more common in the occipital region or at the root of the nose.
- It is present since birth
- It is a cystic swelling, highly translucent, compressible swelling
- Expansile impulse is present when the child cries or coughs
- The overlying skin is normal and free
- On careful palpation the edge of the bony defect is palpable
- Neurological manifestations are usually absent (Compare with myelomeningocele, where neurological manifestations are usually present).
- This condition may be associated with hydrocephalus and this combination is known as Arnold-Chiari syndrome.
- X-ray is confirmatory and will show the bony defect
- Infection and rupture are possible complications
Treatment of Meningocele
An operation should be performed as early as possible, but the child’s condition and strength should be sufficient to withstand the operation. This operation is often performed within a few days of birth.
- The skin and the sac are opened with incisions perpendicular to each other. This will minimize the chance of postoperative C.S.F. leakage.
- The redundant part of the sac is excised
- The margins of the excised sac are sutured together in the midline
- To strengthen the bony gap, the adjacent erector spinae muscle and the overlying fasciae are approximated over the gap with the help of lateral release incisions (to minimize tension in the suture line).
- The skin is closed.
- Meningomyelocele is the commonest variety of spina bifida in the living children.
- The bony defect may usually extend over 3 or more segments.
- Skin may be absent or atrophic, and meninges may be exposed.
- Patient can have spastic or flaccid paralysis.
- Neurological manifestations are almost always present.
- X-ray will show the bony defect. There may be other abnormalities of the vertebrae, like scoliosis or kyphosis or even hemivertebra.
- Other symptoms in infants – lethargy, poor feeding, irritability, stridor or eye coordination problem.
- Older children may present with cognitive changes, motor weakness, spasticity, problems of bladder/bowel, cranial nerve dysfunction, backache or deformities of the lower limb.
- Increase in foot deformities, worsening of spinal deformity or new onset of hip dislocation, progressive neurologic defects in growing children may suggest a tethered cord [tissue attachments cause stretching of spinal cord.]
Based on the level of involvement, myelomeningocele patients frequently can be classified as belonging to one of the following groups, based on the neurosegmental level of the lesion:
- upper limb and neck musculature well innervated
- Function of trunk musculature variable
- No power in lower limbs.
- Variable hip flexor and hip adductor
- Absence of hip extension, hip abduction,
- Absent knee and ankle movements
Thoracic and high-lumbar groups tend to have increased prevalences of lumbar lordosis, abduction and external rotation contractures of hip, flexion contracture of knee and foot equines.
- Present – hip flexors and adductors, medial hamstring, and quadriceps
- Variable – lateral hamstrings, hip abductors, and ankle dorsiflexors
- Absent – Ankle plantar flexors
These often have hip and knee flexion contractures, increased lumbar lordosis, genu valgum, calcaneo-valgus and overpronation of foot.
- Hip, knee normal
- Ankle plantar flexor strength is variable.
These patients often exhibit mild hip and knee flexion contractures and increased lumbar lordosis with variable foot and ankle deformities with various ankle and foot positions.
- Complications of hydrocephalus
- Symptoms of Chiari II malformation- Lower brainstem and/or upper cervical spinal cord compression causing apnea, dysphagia, stridor, nystagmus or upper limb weakness.
- Spinal deformities
- Congenital – vertebrae and rib anomalies
- Acquired due to muscle imbalance
- Lower limb deformities
- Short Stature
- Cranial nerve dysfunction – Ocular muscle palsies, dysphagia and dysphonia.
- Tethered spinal cord – pain, sensory changes, spasticity, and progressive scoliosis.
- Renal Problems
- Neurogenic bowel and bladder
- Bladder incontinence
- Hydronephrosis due to a contracted bladder
- Infections and renal failure
- Vesicoureteral reflux
- Congenital Abnormalities
- Facial clefts
- Heart malformations
- Genitourinary tract anomalies
Treatment of Myelomeningocele
The operation must be performed as early as possible. Child’s condition should also be considered, as it should withstand the operation.
Delay in operation may cause
- Infection within the sac and postoperative problems.
- The sac may rupture and will make operation extremely difficult with infection spreading throughout the subarachnoid space.
- There will be more adhesion of nerves with the wall of the sac, which will be difficult to separate.
- Gradually extensive paralysis of the legs and incontinence may occur, so that surgical intervention may become contraindicated.
Additional Management which may be needed
- Bladder and bowel management
- Bracing and orthotics
- Physical Therapy/ occupational Therapy/ recreational Therapy
- Shunting for hydrocephalus and syringomyelia
- Chiari malformation repair
- Hip relocation and other deformity correction procedures
In this condition, the central canal of the spinal cord is dilated and the spinal cord lies within the sac together with the peripheral nerves arising from the cord.
This is the rarest variety of spina bifida.
Gross neurological deficits and paralytic manifestations are present.
This is the gravest form of spina bifida, in which besides the bony defect there is also a defect of development of the spinal cord. The development is arrested before the time of closure of the neural furrow. So that the posterior part of the spinal cord is not developed.
The elliptical raw surface of the neural furrow can be seen, deep to which lies the anterior part of the spinal cord. At the top end of the defect, the central canal of the spinal cord opens on the surface and discharges the cerebrospinal fluid constantly.
Majority of the cases are stillborn. Even if a few born alive, they die within a few days from infection of the cord and meninges.
Evaluation of Spina Bifida
As the most common type of spina bifida is myelomeningocele, the evaluation discussion is centered around that.
Screening test for neural tube defects can be performed by blood tests or amniocentesis for alpha-fetoprotein estimation combined with ultrasonography. The fetal presence of an open neural tube defect is marked by an elevated alpha-fetoprotein level.
In children with spina bifida, apart from routine laboratory screening examination, urine studies for culture, urodynamic studies for bladder evaluation and latex sensitivity tests become important.
X-rays provide information for early evaluation when an infant is born.
Most of the children on MRI would show a tethered cord but only about 20% are symptomatic.
CT is useful for tracking hydrocephalus.
Prevention of Spina Bifida
Increased use and accuracy of prenatal diagnosis and option for early pregnancy termination and the introduction of primary prevention in the form of folic acid therapy has resulted in a decline of cases of spina bifida.