The term spinal dysraphism encompasses a spectrum of abnormalities, associated with varying degrees of neurological deficits, including spina bifida occulta, occult spinal dysraphism and open neural tube defects. Spina bifida occulta is a radiographic abnormality representing incomplete closure of the posterior laminar arch, and affects about 10 per cent of the population. In occult spinal dysraphism, bony abnormalities are associated with intraspinal defects, including lipomas, dermoid and epidermoid tumours, and thickening of the filum terminale with tethering of the spinal cord. There may be overlying cutaneous stigmata. Open neural tube defects include meningoceles, where there is a cystic outpouching of rudimentary meninges with an underlying intact spinal cord; myelomeningocele, where the malformed neural tube is present at the base of or within the cyst, and myelorachischisis, where the malformed neural tube is splayed over a number of spinal segments, without meningeal coverage.

The symptoms associated with dysraphism vary with the degree of malformation of the underlying neural tissue. Spinal bifida occulta is frequently seen as an incidental finding on routine spine radiographs, most commonly at the L5 and S1 levels. In itself, it is of no neurological significance. When it is associated with overlying skin abnormalities, especially hypertrichosis, cutaneous haemangiomas, lipomas, or a sinus tract, an occult intraspinal lesion should be suspected. These abnormalities may be noted at birth or during childhood, but the patient may be asymptomatic for many years. Some of these children (and, occasionally, adults) develop a progressive neurological deficit involving the lumbosacral roots—the tethered cord syndrome. This appears as bowel or bladder difficulty, foot or leg weakness, sensory loss, muscle atrophy, and pes cavus or scoliosis.

Open neural tube defects present at birth, with an estimated incidence of 1 in 1000 live births, although this shows regional variation. An infant with a meningocele may be neurologically normal, but deficits become severe as more of the placode becomes involved. These lesions are most common in the lumbosacral area, causing abnormalities of bowel and bladder function, as well as variable degrees of leg weakness and sensory loss. Lesions higher in the spinal cord will be accompanied by relatively more severe deficits. In addition to the local neurological deficits, affected infants are at risk of meningitis precipitated by contamination of cerebrospinal fluid from incompetent dura. Other anatomical abnormalities may also be seen, including the Chiari and other intracranial malformations, and 80 per cent of infants with myelomeningoceles have hydrocephalus. Other organ systems are sometimes involved.

The aetiology of these defects remains unclear, though numerous theories have been proposed. Regional variations in incidence have prompted the search for an environmental factor, and numerous teratogens have been suggested. Nutritional deficiencies of folate or zinc have been proposed as contributing factors: a reduction in the incidence of neural tube defects was found when pregnant women received vitamin supplements. The relationship between these predisposing factors and the underlying embryology is even less clear. Genetic factors may play a role, as there appears to be a familial tendency in the occurrence of neural tube defects: the risk of having a second affected child increases from 0.1 per cent to about 5 per cent. Experimental work in mice has suggested that mutant homeobox genes, which appear to control segmentation during embryogenesis, may give rise to the equivalent of neural tube defects, with abnormalities in neurulation, bony development, and overlying integument. Thus environmental teratogens and nutritional deficiencies may act on a common genetic substrate to cause these disorders.

The infant with an open neural tube defect requires a complete neurological examination to document the level of impairment. This level, though sometimes difficult to determine in infancy, can be correlated with future ability to walk independently, with crutches, or to remain wheelchair bound. Radiographic examination of the spine may demonstrate kyphoscoliosis with bony abnormalities of the vertebral column. Head circumference should be monitored, and the presence of hydrocephalus determined by ultrasound or CT. Patients with the occult dysraphic states also require a complete neurological evaluation, with special attention paid to lower extremity function, reflexes, and sensation. Evaluation of bladder function by cystometrogram or electromyography is useful. Radiographic evaluation by either CT/myelography or MRI is required to delimit the underlying anatomical abnormality. The adult conus medullaris should not extend below L1–L2; tethering to a lower level can be seen with a thickened filum, intraspinal lipoma, or other abnormality of lumbosacral development.

Surgical treatment of open dysraphism requires closure of the defect with cyst removal, and often with shunting of hydrocephalus, followed in many cases by multiple orthopaedic and urological procedures to correct the complications of neurological impairment. About one-third of untreated infants die, with the remainder surviving in a severely disabled state. Ethical decision making weighs the quality of life of children subjected to multiple procedures, many of whom have severe persistent disabilities, against the results of withholding treatment. Most paediatric neurosurgeons recommend treatment for all but the most severely affected infants, arguing that, in general, treatment is beneficial for almost all of these children and it is impossible to predict the adult level of intellectual and motor function based upon the necessarily incomplete examination of an infant.

Closure of open defects is performed as soon as possible if cerebrospinal fluid leakage is present (within the first 24 h). An example is shown in Fig. 1 2328,2329. If not present at birth, hydrocephalus may develop after the repair and require shunting. Long-term management of these infants is best handled by a team including paediatrician, neurosurgeon, orthopaedic surgeon, urologist, and nurse specialist, as well as social workers and family support services.

Patients with occult dysraphic states may require surgery to halt or prevent neurological deterioration from the tethered cord syndrome. Although the pathophysiology is unclear, procedures designed to relieve tension upon the cord appear to offer some benefit. Thus sectioning the thickened filum has been advocated, as has removal of a tethering lipoma or dermoid. Because a dermal sinus may lead to recurrent meningitis, it should be excised.