Contents
Introduction
Spina Bidifa is a neural tube defect that results from a defect in the closure of the neural tube (which goes to form the spinal column) during embryological development.
Anatomically, this results in the loss of the posterior wall of the spinal canal (the vertebral arch) and the spinous process of the affect vertebra(e). It can occur anywhere along the spine, but most commonly is found in the lumbar region.
The exact mechanism is not known, but low folate levels during pregnancy are known to increase the risk of the foetus developing the condition.
It can vary from being asymptomatic, through to significant neurological dysfunction distal to the lesion. Generally, the severity of the symptoms correspond to the severity of the defect. Sometimes it is described interns of the examination finding at the site of the lesion:
- Spina Bifida occulta – loss of the spinous process, but no obvious ‘bulge’. There may be excess hair on the skin at the affected site
- Affects up to 10% of the population!
- Spina Bifida cystica
- Meningocele – A bulge of the meninges containing CSF is visible, but the spinal cord remains in its normal anatomical location
- Myelomeningocele – a bulge of the meninges is visible, and the spinal cord lies outside the normal location of the spinal canal, inside this bulge. Often associated with an Arnold-Chiari type II malformation
- Rachischsis – A very severe form of Spina Bifida where the spine may be completely open, and is often associated with anencephaly (absence of large proportion of the brain)
Spina Bifida is often diagnosed prenatally (in the womb) with ultrasound +/- raised alpha-fetoprotein levels in the maternal serum or amniotic fluid.
Spina Bifida may also be associated with hydrocephalus and Syringomyelia (dilation of the fluid filled cavity that runs down the centre of the spinal cord).
In minor cases, no treatment may be required. In more severe cases, surgery may be indicated, followed by a multi-disciplinary approach to minimise functional impact of any residual neurological deficit.
Epidemiology and Aetiology
- F > M
- Up to 10% of the population may have Spina Bifida occulta
- A myelomeningocele affects about 1 in 2000 pregnancies
- Incidence has declined markedly since the introduction of folic acid supplementation in pregnancy
- Genetic component – siblings of those with the condition have a higher risk of neural tube defects
- Risk factors:
- Low maternal folate
- Particularly significant between days 17 and 30 of pregnancy – this is a time when many mothers are not yet aware that they are pregnant – and thus pre-pregnancy planning and supplementation are an important factor in prevention
- Drugs taken in pregnancy – particularly sodium valproate and carbamazepine
- Maternal diabetes
- Maternal alcohol exposure
- Genetic component
- Low maternal folate
Signs and Symptoms
Spina Bifida occulta
Often completely asymptomatic. There are usually no neurological consequences. Physical signs at the site of the lesion not the spine can include:
- A fluid-filled palpable mass
- Altered skin pigmentation
- Excess hair on the skin
- Asymmetrical gluteal cleft
- Sacral dimple
Patients are at higher risk of scoliosis or other spinal deformities than the general population.
In a small number of patients, “tethering” of the spinal cord can occur, resulting in progressive lower limb, bladder and bowel neurological defects as the child grows.
Spina Bifida cystica
Signs and symptoms are very variable and depend on the extent of the lesion.
Neruological
- Possible paralysis and areflexia below the site fo the lesion – especially if nerve roots are involved
- Decreased anal sphincter tone
- If the brain stem is involved (Arnold-Chiari II malformation) there may be stridor, swallowing difficulties and apnoea episodes
Musculoskeletal
- Muscle atrophy of the lower limbs
- Spine deformity and limb dislocations can result from an imbalance of muscle tone
Urological
- Urogenic bladder
- Vesicoureteric reflux
- Hydronephrosis
- Recurrent UTI
Diagnosis
Diagnosis is usually clinical after birth, from a combination of lower limb, bladder and bowel neurological signs, and deformity of the spine.
Prenatal diagnosis
- The 18-20 week foetal anomaly scan can detect neural tube defects
- At 16-18 weeks, raised levels of alpha-fetoprotein (AFP) are delectable in the maternal blood, but this test is non-specific
- Amniiocentesis can be performed to assess fluid AFP and acheylcholinesterase levels. This can differentiate between types of neural tube defects.
Post-diagnosis work-up
Patients should be assessed for evidence of associated abnormalities:
- U+Es to assess renal function
- Urine MC+S
- Urodynamics
- Latex allergy testing
- ELISA or skin prick testing
- Up to 40% of spina befit patients are latex allergic – possible because of repeated surgical exposures form a young age
- Plain spine x-rays
- To look for scoliosis and other associated spinal abnormalities
- CT or MRI of the brain and spinal cord
- Looking for Arnold-Chiari II malformation, hydrocephalus and other abnormalities
- Can assess for tethering of the spinal cord
- Assessment of neurological deficit and gait
Complications
- Meningitis
- Fractures
- Hip dislocations
- Pressure sores
- Hydrocephalus
- Neurogenic bladder
- Constipation
- Latex allergy and anaphylaxis
Management
Management depends on the severity of the spinal bifida. In more severe cases, a multidisciplinary approach is best, with the aim to reduce the risk of complications – particularly hydrocephalus.
Spina bifida occulta often may not require any specific management.
Spina bidifa cystic is extremely variable, but will often require surgery.
In severe cases, then fetal surgery before 26 weeks gestation may be considered. This can prevent herniation of the brain and Chiari II malformation, and reduce the need for ventriculoperitoneal shunt after birth.
Acute management
- Neonates with open neural tube defects should be kept in prone position with the NTD covered by saline soaked dressing
- Arrange for urgent surgical assessment
Long-term management
These interventions aim to improve functioning in the long term
- Physiotherapy
- Occupational therapy
- Consider bracing
- Regular orthopaedic review
- Spinal fusion, or other joint surgery may be required
- Regular paediatric assesment
- Avoiding weight gain is particularly important. Patients are often less active than the general population and prone to weight gain, which is associated with increased morbidity
- Regular neurosurgical assessment
- To detect hydrocephalus and tethered spinal cord
- Psychological assessment and assistance – for both patient (As they grow) and family as required
- Bladder and bowel assesment
- Regular self-catheterisation may be required
- Assistance with bowel emptying
Prognosis
- Vast majority of patients have normal physical and intellectual development
- Even those with myelomeningocele can lead a relatively normal life with early and appropriate treatment
- Patients wit a lesion at L2 or higher have a worse prognosis, especially if associated with hydrocephalus
- Causes of untimely death include:
- Epilepsy
- Urinary sepsis
- PE
- Acute hydrocephalus
References
- Spina Bifida – Patient.info
- Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
- Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt