Spina Bifida

Synonym: Spina bifida cystica/occulta, neural tube defect (NTD), myelomeningocoele.

This is a congenital abnormality of the structural form and covering of the nervous system; collectively, such anomalies are termed neural tube defects. There is a spectrum of abnormalities, outlined below:

The incidence varies between populations, with those of Celtic origin having the highest incidence historically at about 3–4 cases of myelomeningocoele per 1000 births. Overall UK incidence was 2–3.5 cases per 1000 births,³ but has now fallen to roughly 10 per 10,000 live and still births, a similar prevalence to that found in the rest of Europe.² This is thought to be due to a combination of prenatal diagnosis and termination of pregnancy and improvements brought about by better diet and folic acid supplementation.

• In cases of spina bifida cystica the abnormal herniation of the dural contents is usually evident either at birth or during antenatal ultrasound scanning.
• The lumbar and lumbosacral regions are most commonly affected by spina bifida cystica.
• In cases of meningocoele alone (where there is only a herniation of the meninges which is often covered by skin) the lesion may be difficult to detect, although overall prognosis is much better than in myelomeningocoele.
• Spina bifida occulta is more difficult to detect but is associated with long-term complications; it is often associated with an overlying skin abnormality such as hairy patch, dermal sinus tract, dimple, haemangioma or lipoma. If such a lesion is below the superior limit of the gluteal fold then it is unlikely to be of significance, but if above this region usually indicates spina bifida occulta that may be associated with complications.⁴
• The disruption of spinal cord function causes sensory dysfunction, paralysis and areflexia below the affected level; an alternative pattern is the preservation of some distal reflex activity which is usually exaggerated.

• The classical appearance of spina bifida cystica is not likely to be confused with other pathologies.
• Myelomeningocoele must be distinguished from meningocoele due to their differing outlook and treatment, and this will usually require neuroimaging with CT or MRI.
• A subtype of spina bifida cystica known as lipomeningocoele/lipomyelomeningocoele has an overlying lipomatous mass that herniates through the bony defect and attaches to the spinal cord, tethering it and, often, its associated nerve roots.
• It is unusual for such lipomatous lesions to have associated hydrocephalus but they do tend to have a worse prognosis than simple meningocoeles.
• A rare subgroup of spina bifida cystica called myelocystocoele is due to the terminal spinal cord being affected by a large cystic dilatation. The posterior spinal cord is often attached to the skin and not properly differentiated giving rise to a large terminal skin-covered sac. Such masses may lie anteriorly and cause a pelvic mass.

Pre-natal diagnosis

Measurement of alpha feto-protein (AFP) in maternal blood at 15–20 weeks gestation is carried out as part of the 'triple-test' screening programme for fetal abnormality. This test can allow detection of neural tube defects. It is significantly elevated in cases of spina bifida, although it is not a specific test and further evaluation through ultrasound screening and amniocentesis is usually needed when an abnormal maternal blood result is picked up. The 18–20 week fetal anomaly screening ultrasound scan also allows detection and diagnosis of neural tube defects and is much more specific.⁵

Investigation of a confirmed case of spina bifida

• Screening bloods will be carried out to detect any evidence of impairment of other organ systems, particularly renal impairment.
• Urine culture and cystography may be needed to detect any abnormality of the urinary tract caused by impaired bladder innervation.
• Latex allergy is relatively common among sufferers of spina bifida, probably due to inherent susceptibility and repeated exposure to surgical procedures;⁶ ELISA or skin-prick sensitivity testing may be needed to avoid illness caused by latex exposure.³
• Plain x-rays of the spine will detect any associated scoliosis and hip dysplasia, which is associated relatively commonly with spina bifida.
• CT and/or MRI of the head and spinal cord are conducted to look for evidence of the major complications of spina bifida such as:
  • Hydrocephalus due to Arnold-Chiari II malformation (malformation of the cerebellum and elongation of the cerebellar tonsils with the cerebellum drawn into the fourth ventricle)
  • Tethering of the spinal cord by fibrous bands.
• Gait analysis may be needed to evaluate a patient's functional mobility and allow intervention to improve independent mobility through the use of orthoses or surgery.

The classification system below has been developed to inform choices relating to the utility of orthopaedic surgery, particularly the need for hip surgery and other orthopaedic procedures designed to improve independent mobility:⁷

• Community ambulator – Mobile indoors or outdoors using crutches, with or without braces
• Household ambulator – Mobile indoors only using crutches, with or without braces
• Nonfunctional ambulator – Wheelchair user but able to use crutches and braces during therapy or intermittently
• Nonambulator – Wheelchair user on a permanent basis

• Extensive multidisciplinary care is needed to maximise mobility, prevent or ameliorate CNS complications of spina bifida (particularly hydrocephalus), encourage normal development and maintain as independent a life as possible.
• Management may start in the antenatal period through the use of fetal surgery. There is good evidence that operating to repair myelomeningocoele in fetuses that have had the condition detected by ultrasound scanning, before 25 weeks gestation, with a lesion below the level of L2, reduces the incidence of the development of shunt-dependent hydrocephalus.⁸ The surgery is thought to improve CSF pressure dynamics and reduce the purportedly damaging effect of exposure of CNS tissue to amniotic fluid.⁴
• In those patients who do not have prenatal surgery, there is a need to close and repair the spinal herniation and defect, and insert a ventricular shunting device if there is evidence of, or a likelihood of, hydrocephalus.⁹
• Where patients do develop hydrocephalus due to the Arnold-Chiari II malformation then ventricular shunting may be necessary at a later stage.
• Ongoing management of mobility utilising orthopaedic assessment, bracing and orthopaedic surgery is often necessary. Spinal fusion, hip and pelvic or foot/ankle procedures are often needed. Prolonged physical therapy, access to gym resources and/or adaptive training in children can be very helpful in maintaining independence and mobility.
• Developmental assessment by a paediatrician and help with maintaining a normal weight (weight gain is common due to impaired ambulation and can increase morbidity) are useful.
• Psychological input for the sufferer and their family to deal with the ramifications of their condition as they grow older is often needed.
• Neurosurgical follow-up is necessary to detect and treat complications such as hydrocephalus.
• Bladder and bowel function can be maintained or aided by the use of a regular bowel voiding regimen and intermittent clean self-catheterisation.

• Fractures, particularly of lower limb long bones and hip dislocations, which may be asymptomatic
• Skin ulceration around orthoses/braces
• Hydrocephalus due to Arnold-Chiari II malformation causing developmental impairment
• Neurogenic bladder causing incontinence and urinary tract infection
• Constipation due to impaired bowel innervation and anal sphincter function
• Latex allergy leading to anaphylaxis.⁶

• Nowadays, with the advent of prenatal surgery, early repair of postnatal myelomeningocoele, shunting to prevent hydrocephalus and expectant management of complications, most patients born with spina bifida survive into adulthood and develop relatively normally intellectually.
• Ambulatory prognosis is largely dependent upon the level of the lesion and strength of quadriceps muscle.
• Long-term survival is dependent on adherence to appropriate bowel and bladder regimens and careful management of urinary complications to prevent renal failure.
• In a UK-based survey of patients born between 1963 and 1971 and surveyed 20 years later:¹⁰
  • 50% had died (largely the most severely disabled)
  • 84% of survivors required CSF shunting
  • 70% had an IQ>80
  • 37% lived independently in the community
  • 39% drove a car
  • 30% could walk >50 m
  • 26% in open employment
  • One-third needed daily care
  • A minority of patients had severe dependency/disability – need for respiratory support, blindness and dialysis-dependence
  • Those who had a need for CSF-shunt revision had worse outcomes in terms of attainment and independence
• It is hoped that overall prognosis will be improved by the advent of prenatal surgery and better expectant management of spina bifida sufferers, particularly in terms of prevention of hydrocephalus.

• Peri-conceptual supplementation of folic acid and improved folate content in the diet of the general population.^1,2
• Improved prenatal diagnosis and prenatal surgery/termination of some pregnancies may reduce the future burden of disability caused by this condition.