Spina Bifida
Introduction
Spina bifida (SB) is the term used for a spectrum of congenital neural tube
defects (NTDs). Other terms used for these anomalies are spinal dysraphisms
or myelodysplasias. NTDs are complex medical problems which challenge surgeons
and paediatricians alike, both in their initial management and in their life-long
complications. While SB may become a vanishing disease in developed countries,
it remains a very significant cause of morbidity and disability in the developing
world.
Epidemiology
The key epidemiologic features of SB are: wide regional and ethnic differences
in prevalence, a world-wide decline in prevalence over the past 3 decades,
and female preponderance (1). The reasons behind the decline
are unclear and most likely multi-factorial, though both folic acid supplementation
/ fortification and selective termination of pregnancies are key factors (2).
The range in prevalence in Western nations is roughly 0.1 – 1 per 1,000
live births; a few non-Western studies often quote higher rates, though again
widely spread.(3-5)
Embryology and Etiology
Spina bifida may result either from failure of closure of the neural tube,
or from secondary re-opening of a closed tube, although most of the evidence
favours the former theory. (6)
The etiology of SB is multi-factorial (1). Evidence for a
genetic component is evidenced by the familial risk. This appears to be 20-50
per 1,000 if one child is affected, 100 per 1,000 if 2 children are affected,
and 30 per 1,000 if the mother is over 35 years of age (2).
Environmental factors include low socio-economic factors, maternal hyperthermia,
and medications. The latter include primarily carbamazepine, valproic acid,
and folate. The use of carbamazepine and valproic acid causes a 1% risk of
SB infants in mothers taking them.
Folic acid, on the other side, has been conclusively shown to both prevent
the first occurrence of SB defects in pregnant women and to cause a 70% reduction
in recurrent SB in mothers who already had pregnancies with NTDs (7).
Based on the overwhelming evidence for folic acid importance in preventing
NTDs, folate supplementation of at least 400 µg daily has been uniformly
recommended for all women of child-bearing age. However, the difficulty in
reaching this wide group at risk makes food fortification a much better method,
adopted in most developed countries. (8) This policy, if
implemented fully, is expected to result in a 50% reduction in NTDs. Unfortunately,
only 10% African countries have been able to implement this policy (9).
Spectrum of defects
The obvious (apparent) spinal defects include myelomeningoceles, meningoceles
(together referred to as spina bifida cystica), and lipomeningoceles. Occult
lesions include diastematomyelia (split cord), tight filum terminale, dorsal
dermal sinus, and spinal lipoma. The term spina bifida occulta should be reserved
for spinal bone fusion defects only.
Associated conditions
Children with SB frequently have associated congenital anomalies. These include
primarily renal and orthopaedic problems, which will be discussed later. Other
associations are undescended testes in males and anorectal anomalies. In fact
up to 50% of children with anorectal anomalies have a tethered cord (6).
The main neurological association with SB is the Chiari II malformation, present
in most cases of SB (2). Rather than a single anomaly, this
is in fact a constellation of brain and spinal cord anomalies specifically
associated with SB. Its key feature is hindbrain (cerebellum, pons, medulla)
herniation into the cervical canal, and is responsible for the frequent hydrocephalus
(HC) in children with spina bifida (6;10).
Other neurological associations of SB are tethered cord (discussed later)
and syringomyelia. The latter is a dilation of the central canal of the cord
with CSF, and is found asymptomatically in most patients with SB (2).
Diagnosis
Prenatal screening for SB includes maternal AFP, acetylcholinesterase, and
ultrasound (1). In utero treatment for the spinal defect
remains experimental (11), and for the associated hydrocephalus
is associated with an unacceptable mortality (6). The effect
of mode of delivery (vaginal vs. cesarian section) on neurological defect
is controversial and remains under study (1).
Neonatal assessment
and management
The patient born with an open SB defect must be managed with immediate saline
coverage of the defect, prone positioning, and the start of intravenous antibiotics.
Neurotoxic iodine-based solutions should not be applied to the defect. The
physical assessment of the child needs to be comprehensive, as listed in the
table below.
Physical Examination of the child with spina bifida
The appearance of the spinal defect reveals its identity: myelomeningoceles
usually have a central “open” defect without normal skin, often
with a visible placode (the open spinal cord). They may appear flat at birth,
then often fill up with CSF. Older unoperated children will often have significant
scarring, and the skin may indeed completely close the defect. Meningoceles
and lipomeningoceles are fully skin covered from birth, with the former typically
cystic and the latter fatty in consistency.
The distribution of the levels of SB depends on referral patterns and access
to care, but usually about 40% are lumbosacral, 30% lumbar, and 30% thoracic
or thoracolumbar. (12) The accurate assessment of the spinal
cord function is critical. It must be kept in mind that the skin level of the
defect may not accurately reflect the spinal level, that children may exhibit
both upper and lower motor neuron lesions, and that the level may be asymmetrical.
Hydrocephalus occurs in 80-90% of infants with spina bifida (1),
but may not be apparent until the spinal defect is closed. It is less frequently
seen in children with sacral defects. Our experience as well as other reports
may point to a lower incidence of hydrocephalus in developing countries. (12)
The Chiari II malformation may also cause specific hindbrain herniation symptoms
in about 20% of SB children. These symptoms include apnea, a high-pitch cry,
and swallowing difficulties (2;6).
Initial investigations
There are no immediate investigations that are required in a regular case of
SB. Spinal X-rays may reveal other occult dysraphisms in 10% of patients (6),
though this will likely not affect the management. Magnetic resonance (MR) imaging
of the spine is frequently performed in developed nations, though hardly necessary
if resources are limited. An ultrasound of the head for hydrocephalus is useful,
though the ventriculomegaly may not be evident until the CSF leak through the
spinal defect is closed. There are several investigations for the GU system
which will be discussed under that heading.
Differential diagnosis
The differential diagnosis of SB is limited. Sacrococcygeal teratomas may mimic
large sacral neural defects, though their appearance is usually more heterogeneous,
they have no open placode and often surround the anal canal. Lipomas of the
midline back may mimic lipomeningoceles, and therefore require spinal XRs and
even MR imaging to exclude an association with the spinal canal.
Initial surgical management
The management of a child with spina bifida is lengthy and complex (2;13).
The closure of the spinal defect is the most obvious step, though it is by far
not the most challenging one. While major associated congenital anomalies may
lead to a palliative approach without surgery, the level of the defect should
not affect that decision. While some have advocated in the past a selective
approach to SB (14;15), there is good evidence
that a non-selective approach yields equally good results compared with a selective
approach, while giving a chance for life to many more children (2;16).
In fact the overall mortality and the intelligence quotients (IQs) of the unselected
groups compare favourably with that of the “best” infants from the
selected group (2). Looked at differently, 60% of the children
from the selected group, who were allowed to die, would have been “competitive”
if allowed to survive (2).
On the other side, occasional older asymptomatic children coming with relatively
small defects which are fully skin-covered and mostly scarred may not need to
have their defect “closed”, especially as the surgery in those instances
can be very difficult and dangerous. Such children will however need to be carefully
followed up for the appearance of tethered cord symptoms and signs.
In the newborn with SB the spinal defect should be closed ideally within the
first 2 days, though delays within the first week of life while the child is
on antibiotics do not seem to affect adversely the outcome (1).
In developing countries children typically present after the first week of life
(12;17), and the defect is often grossly
infected. While preoperative intravenous antibiotics are the rule in all settings,
there is little advantage to lengthy preoperative courses of antibiotics and
dressings.
Operative approach
The standard repair of an open SB includes the following steps (2;6;18):
Variations to the above steps may include:
Postoperative care
The multitude of interventions in the immediate post-operative care are illustrated
in figure 1 –
the spina bifida care pathway used at our institution. Such protocolized
care facilitates team care and improves outcomes.
Post-operative complications
Wound problems are frequent, including infection, dehiscence, and necrosis (12;14;18).
They can be managed almost always conservatively with dressings, debridement,
and sitz baths. CSF leaks may occur (12;12),
and although most will resolve with time and control of the CSF pressure (with
shunting or acetazolamide), persistent leaks may require re-exploration.
Re-tethering of the cord at the repair site occurs in 15-20% of cases long-term
(6), and requires prompt surgical untethering.
Management of Chiari II
problems
While concomitant shunting for HC at the time of the neonatal spinal defect
closure is standard in developed nations, the approach must differ in the developing
world. In our experience and that of others in Africa, early shunting leads
to frequent shunt infection and ventriculitis. Our practice is to wait at least
a week after the spinal closure for shunting, or longer if there is any evidence
of wound infection. Mild stable hydrocephalus with a cortical mantle of at least
3.5cm can be observed safely for several months without deleterious effects
(2).
Other Chiari II symptoms and signs (apnea, stridor, poor swallowing) are initially
managed by decreasing the intra-cerebral pressure (ICP) through shunting (6).
Persistent symptoms may require a posterior fossa decompression (2;6),
though this procedure is challenging and should be reserved to specialized centres.
Musculoskeletal management
Scoliosis and/or kyphosis are the most common orthopaedic associations of SB.
They develop in up to 60% of children with SB (12), especially
in children with thoracic defects (2). Seating appliances can
help, but braces are of questionable value and surgical management (spinal fusion)
is very challenging.
Talipes equinovarus (TEV, club foot) is the next most common orthopaedic problem
(12). Ideally it is treated conservatively though casting
in the neonatal period, while, later on, a postero-medial release may be required
(19). Other lower extremity problems include high arch foot
deformity, leg discrepancy, flat foot, foot valgus, and congenital dislocation
of the hip (12).
Adults with SB appear to develop multiple degenerative musculoskeletal problems
including osteoarthritis and osteoporosis.
Depending on the motor level, patients with SB may require a variety of orthotic
devices to allow partial or full ambulation. These include above- and below-knee
braces, crutches, walkers, and wheelchairs (2). Traditional
teaching states that independent ambulation is possible if the quadriceps are
strong (L3-4), but long-term studies have shown that the mobility of children
with SB decreases with age despite stable neurological status (2;6).
Gastrointestinal
management
Nutritional problems are frequent in the SB population. While in developed nations
obesity from limited activity is common, many children with SB in the developed
world suffer from nutritional deficiencies.
Defecation problems are however the main challenge in this population. (20;21)
Constipation occurs predominantly in children with high lesions, due to slow
colonic transit, and in children with sacral lesions, because of deficient rectal
sensibility (22). Constipation may be managed through dietary
manipulation combined with regular finger stimulation or manual evacuation.
Fecal incontinence is much more of a challenge, with at least half of children
being affected(12;22). Children with lumbosacral
lesions often have pellet-like stools from slow left colonic transit, evacuated
without voluntary control despite fair sphincter function. They are best managed
with intentional constipating foods and daily manual evacuation. School-age
children who fail this regimen should first be tried on retrograde washouts
every 1-3 days (22;23). The next step is
the ACE procedure (antegrade colonic enemas)(23;24).
In this procedure the child’s colon is cleaned daily with a small volume
of water and/or paraffin administered through a cutaneous appendicostomy. In
developed countries this procedure has been modified to use a small cecostomy
“button” device inserted under radiographic guidance (25).
The standard cutaneous appendicostomy however is quite effective and well-suited
for the developing world.
Integumentary problems
Decubitus ulcers occur frequently in patients with SB, especially beyond the
age of 5 years (12). They represent therapeutic challenges.
Similarly to ulcers in other patients with neurological deficits, a conservative
approach with saline dressings and avoidance of pressure areas is always warranted.
Refractory ulcers can benefit from plastic surgical procedures, though recurrences
are frequent.
Other ulcers in these patients are found in the perineal area and are caused
by urinary and/or stool incontinence. These ulcers must be managed by attempting
to address the underlying incontinence problems.
Latex allergy
Latex allergy is an IgE-mediated problem leading to the spectrum of urticaria,
bronchospasm, and anaphylaxis. While latex allergy is a frequent (20-30%) complication
in children with SB in developed countries (26;27),
it is rarely reported in the developing world and also in our own experience.
Some evidence from South Africa suggest a lower overall incidence compared to
western nations (28).
Urological management
Spina bifida is the main cause of neurogenic bladder dysfunction, which leads
to hydronephrosis, vesico-ureteric reflux (VUR), and ultimately renal failure.
(29;30) One half of untreated patients with
SB will experience these complications, which in fact constitute the main cause
of mortality in this population (31).
The bladder dysfunction in SB patients can be classified by the interplay between
the bladder and sphincter muscles in 3 groups: synergic (both muscles acting
in unison, 19%); dyssynergic with/out detrusor hypertonicity (DSD) (45%), and
denervated (36%).
The basic urological work-up of patients with SB includes renal ultrasound,
serum creatinine, and volume urodynamics. These include leak-point pressure
(LPP) and post-void residual (PVR) values, both measured using a simple burette
and 3-way stopcock apparatus (32). More sophisticated electromyography
(EMG) urodynamics are not necessary in most instances.
The mainstay in the treatment of the neurogenic bladder of children with SB
is clean intermittent catheterization (CIC). This procedure is simple to perform
and to teach in all patient groups, cheap, safe (33), and
very efficient. It has revolutionized urological care in SB and is well suited
for resource-poor settings. It is most efficacious when started in infancy,
though it can be started at any point in time. It is performed by the main caregiver
of the child until the age of 6-7 years, after which self-catheterization can
be taught (33). In our institution we perform volume urodynamics
3 days after the closure of the spinal defect, then immediately teach the caregivers
to perform CIC if the volumetric criteria are met. These include an LPP = 30cm
or a PVR = 10cc (32). Other criteria we use include laboratory
evidence of renal dysfunction (abnormal renal ultrasound, creatinine or urinalysis),
recurrent urinary tract infections, and the need to promote social continence
in older children.
CIC may need to be complemented with medications. These are detrusor overactivity
relaxants such as oxybutinin and imipramine, administered either orally or intravesically.
CIC with or without medications will prevent renal deterioration in 90% of children
with SB, and achieve social continence in about 85% (2). Only
a minority of patients should require urological procedures, such as bladder
augmentation, bladder neck reconstruction, or urinary diversion (30;34;35).
However, long-term renal follow-up is essential in all SB patients. We advise
yearly renal ultrasound and volumetric urodynamics. While in developed countries
renal transplantation is ultimately the treatment of choice for renal failure
(31), this is rarely an option in developing countries.
Prognosis
The mortality in patients with SB appears to be between 25-50% into adulthood
(2;27), and naturally higher in developing
countries. Renal failure is a common cause of late mortality, as well as sepsis
and shunt complications (36).
Over 85% of the patients have ventriculoperitoneal shunts, with most of them
having undergone at least one revision (27). A third of the
patients have undergone a tethered cord release, and half have scoliosis. The
same long-term Western study however showed that 85% of patients are attending
or have graduated from high school and/or college, and more than 80% have social
bladder continence (27). Another British study found a 50%
mortality after 30 years, while among the survivors 70% had an IQ of 80 or more,
37% lived independently in the community, 39% drove a car, 30% could walk more
than 50 meters and 26% were in formal employment (37).
Results from developing countries are rather scanty. A Nigerian study found
that 40% of children with myelomeningoceles were “functionally disabled”
and could not be adequately rehabilitated because of limited resources (14).
The authors therefore advocated a selective management. A South African study
revealed a 70% ambulation rate, 45% urinary continence, and a mean IQ of 80
(17). As expected, their results were better in urban areas
and in the higher socio-economic groups. Our own experience has shown that 64%
of children with SB over the age of five had some from of independent mobility.
Interestingly, quality of life in SB appears strongly influenced not only by
neurological characteristics, but also by “soft” factors such as
parental hope.
Other spinal dysraphisms
Meningocele
Meningoceles are defects of the dura, arachnoid, and dural pouches without neural
elements (6). They arise primarily posteriorly, though anterior
and lateral defects are also seen. The affected children will therefore be mostly
intact neurologically, and the incidence of HC is also low (though not nil).
Intra-operatively often a fibrous stalk is found connecting the underlying cord
to the cyst wall, and this needs to be totally excised to prevent re-tethering.
Lipomeningocele
This is another occult dysraphic state, formed by a partial dorsal myeloschisis
with a lipoma fused to the dorsal aspect of open cord. It is caused by the inner
neural tube inducing mesenchyme to differentiate into fat (38).
Clinically it is similar to the meningocele in being fully skin-covered, though
its consistency often reveals the fatty composition. Neurological deficits are
usually absent at birth, appear after the second year of life, and affect most
patients by early childhood (6). Patients are typically referred
for a fatty mass in the midline lower back, occasionally extending into one
buttock. Half of the patients have an associated cutaneous marking (38).
While the appearance may not be very impressive, these defects are notoriously
difficult to repair, as the lipomatous tissue is intricately associated with
the nerve roots and the dura. A magnetic resonance (MR) scan is very important
in revealing the extent of the abnormality (6). While a partial
resection is possible and may help cosmesis, it is inappropriate as the tethering
of the cord remains. Lipomeningoceles are not surgical emergencies and therefore
should only be repaired in specialized centers using operative magnification.
Repair entails proximal laminectomy, careful dissection of the fatty tissue
with untethering of the cord, and dural reconstitution for closure (6).
Post-operative CSF leaks are frequent in our experience.
Occult spinal dysraphisms
– tethered cord syndrome
There is a wide spectrum of other occult spinal dysraphisms, including intradural
lipoma, diastematomyelia, tight filum terminale, dermoid cyst/sinus, aberrant
nerve roots, anterior sacral meningocele, and cauda equina tumor (6).
They are relatively rare conditions, though it is known that up to one third
of the population has occult spinal defects (39).
Most occult dysraphisms are signaled by cutaneous abnormalities, such as dimples,
tufts, sinuses, vascular malformations, or lipomas (12;12;40).
The patients may be totally asymptomatic, though many will develop a tethered
cord syndrome with age, particularly during significant growth spurts. Most
symptoms are musculoskeletal (high arch, abnormal toes, leg discrepancy, abnormal
gait) and urological.
A tethered cord syndrome (41) must be therefore suspected
and ruled out whenever a patient of any age develops new or progressive weakness
and/or spasticity, a deteriorating gait, change of bowel/bladder function, back
or leg pain, progressive scoliosis or foot deformity (6). While
there may be significant pain, the neurologic signs and musculoskeletal deformities
(especially lordoscoliosis and contractures) may be subtle. Occasionally, a
change in urodynamic studies in a patient with previously repaired SB may be
the first clue.
Confirmation of the clinical diagnosis of tethered cord requires MR, and the
treatment is prompt surgical untethering.
Dan Poenaru MD, MHPE, FRCSC, FACS, FICS, FCS-ECSA
Adjunct Professor of Surgery and Paediatrics, Queens’ University, Kingston,
Canada
Hon. Professor of Surgery, Aga Khan University, Nairobi, Kenya
Medical Education & Research Director, AIC Kijabe Hospital
Kijabe, Kenya
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