The term spina bifida encompasses a spectrum of abnormalities of development of spinal vertebrae and the spinal cord, ranging from the absence of a single vertebral spinous process to craniospinal rachischisis—failure of neural tube closure incompatible with life. All of these conditions have in common a failure of the bony spinal column to close fully, defining a ‘bifid’ spine. The frequent associated defects in neural development, skeletal structure, and urological function make this an anomaly with which even the general paediatrician and paediatric surgeon should be familiar. Current and continuing advances in the understanding and treatment of open neural tube defects, hydrocephalus, congenital urinary dysfunction, congenital extremity weakness, and developmental delay promise an acceptable quality of life for almost all spina bifida patients.

The range of defects defined as spina bifida may be conveniently divided into several clinical groups:

(1)incidentally discovered occult bony defects of the spine with no spinal cord involvement (incidental spina bifida occulta) (Fig. 1) 2228;

(2)abnormalities of the spine and spinal cord resulting in the tethered cord syndrome (occult spinal dysraphism);

(3)open neural tube defects that may communicate with the outside (myelomeningocele or spina bifida aperta). The expression of the last two entities is associated with a characteristic constellation of clinical and anatomical abnormalities.

Incidental spina bifida occulta is found in up to 30 per cent of the general population and has no clinical significance. The incidence of occult spinal dysraphism is unknown; however, its clinical presentation as the tethered spinal cord syndrome is uncommon. Risk factors for tethered cord syndrome have not been defined, nor have significant demographic data been collected. In contrast, there are striking geographic differences in the incidence of myelomeningocele, as well as a trend toward reduced expression of this defect in the past 50 years. Currently, the incidence of myelomeningocele is approximately 1 per 1000 live births. There is a higher incidence in females. Children of black and Asian subjects are at lower risk for myelomeningocele than are children of whites; risk of neural tube defects also decreases with higher socioeconomic status. These observations have not led to a secure genetic or environmental aetiology for spina bifida.

Spina bifida tends to occur in families: although the risk of an open neural tube defect is 0.1 per cent, birth of a first child with myelomeningocele raises the risk for a second child to 5 per cent; having two children with myelomeningocele leads to a 15 per cent risk that a third child will be affected. These observations suggest non-Mendelian penetrance of a recessive trait, or a multifactorial aetiology for the spina bifida defect. For this reason, genetic counselling should be offered to all couples with a family history of myelomeningocele.

The neural tube closes in humans at 26 to 28 days of gestation. Spina bifida can arise from either primary failure of neural tube closure at that time or secondary rupture of a closed neural tube after embryonic day 29. Both of these possibilities are under investigation: evidence based on experimental production of neural tube defects by timed administration of toxins has failed to distinguish a uniform aetiology. The wide range of anomalies encompassed by and associated with spina bifida suggests that more than one embryological defect may be implicated.

The pathology of spina bifida reflects the varied severity of the anomaly as well as the possibility that other systems in the body may harbour congenital defects. Incidental spina bifida occulta is represented by normal spinal cord anatomy, normal spinal column alignment, and the replacement of one or more dorsal spinal laminae by fibrous tissue, defining the open spinal column. In occult spinal dysraphism the bony anomaly is associated with a number of abnormalities within the spinal canal. These include a thick filum terminale, intradural epidermoid and dermoid cysts, intradural lipoma (lipomyelomeningocele) (Fig. 2) 2229, teratoma, diastematomyelia (local midline splitting of the spinal cord with interruption by a midline bony or fibrous peg) (Fig. 3) 2230, or a combination of abnormalities. Intradural pathology causing a tethered spinal cord is often associated with some type of overlying skin abnormality, such as hyperpigmentation, dermal sinus tract, or a hairy patch. There are generally no other associated central nervous system anomalies (such as hydrocephalus or the Chiari malformation) in occult spinal dysraphism. The spinal cord is usually normal except in relationship to the distal tethering.

A myelomeningocele sac is found where the spinal column and spinal cord have not fused in the midline. An outpouching of neural tissues, spinal meninges, and other midline structures that have not fused are found under a layer of skin or a thin membrane (Fig. 4) 2231. Eighty-five per cent of myelomeningoceles are thoracolumbar or sacral. The most dorsal neural tissue found in the defect, the neural placode, is splayed, unfolded spinal cord tissue which is adherent to the skin or membrane covering. Though generally non-functional, distal spinal cord tracts and lumbosacral nerves can traverse the myelomeningocele sac and are potentially active. Dorsal structures, such as the arachnoid lining, dura, and skin may meld into the lateral edges of the open tube-like structure, or may close on the midline. Lipoma, dermoid, epidermoid, and other tumours may be associated with these structures at any layer from cord to skin. Pathophysiologically, it is unusual to find useful neural function distal to the neural placode. However, spinal cord neurones and sensorimotor tracts are anatomically evident at all levels of the spinal cord of spina bifida patients. The reason for distal paralysis remains unknown, but this observation emphasizes the need for protection and reconstruction of all neural tissues evident in a neural tube defect.

Brain anomalies associated with myelomeningocele include hydrocephalus, agenesis of the corpus callosum, lobar agenesis, polymicrogyria, rim-cortex (holoprosencephaly), intracranial cysts and lipomas, and encephaloceles. Outside of the nervous system, anomalies of the skeletal, genitourinary, cardiopulmonary, and gastrointestinal systems are common (Table 1) 583. The likelihood of associated somatic anomalies increases with the severity of the neural tube defect; however, on average a child can be expected to have more than one abnormality.

Family history of spina bifida is an indication for further evaluation of an unborn child. Antenatal ultrasonography and measurement of maternal serum and amniotic fluid alpha-fetoprotein levels provide a reasonable ability to diagnose open neural tube defects antenatally. An open spinal column or a meningocele sac are readily apparent on an obstetrical ultrasound examination. Elevated maternal serum alpha-fetoprotein levels can be associated with myelomeningocele and should prompt a close ultrasonographic examination. Counselling the parents of a spina bifida child is of the utmost importance, particularly when the diagnosis is made antepartum. Open discussion of options for treatment and outcome can allay many fears and misconceptions prevalent in our society.

The central nervous system is not generally affected in patients with either incidental spina bifida occulta or tethered cord syndrome. The skin overlying a purely incidental bony bifid spine is usually normal and there is no specific course of evaluation or treatment. As described, a spinal bony defect associated with a skin abnormality, or with back pain, scoliosis, and enuresis may be indicative of a tethered spinal cord. Suspicion of any of these lesions requires further evaluation with magnetic resonance imaging or myelography and CT.

Tethered spinal cord can present at any age as back pain, lower extremity weakness, or bowel and bladder changes; however, most cases present in early childhood. The presence of a subcutaneous lipoma or another cause of a tethered cord is often noted anatomically before symptoms occur. Even when neurological complaints are absent, surgery to prevent deterioration is indicated in children with such lesions. Any patient with progressive complaints requires urgent evaluation and treatment. If appropriately repaired, patients with an occult spinal dysraphic lesion can often show entirely normal development and function.

Clinically, myelomeningocele is diagnosed at birth by the presence of a midline mass covered by skin or membrane which contains dural and neural elements (Fig. 5) 2232. As this sac is continuous with the cerebrospinal fluid space, care must be taken to avoid infection. Since common associated anomalies include Chiari type II malformation of the hindbrain, hydrocephalus, orthopaedic anomalies of the spine and lower extremities, and bladder and bowel dysfunction, a multidisciplinary team including paediatricians, neurosurgeons, orthopaedic surgeons, and urologists is best equipped to manage a child with myelomeningocele. Evaluation should include neonatal ultrasonography, magnetic resonance scanning, plain spinal radiography, and urodynamic testing. Treatment is initiated immediately after birth by urgent closure of the defect and referral to a multidisciplinary center experienced in the treatment of myelomeningocele. Cerebrospinal fluid shunting is required in more than 90 per cent of patients, and a series of orthopaedic and urological interventions is almost universal. Complications caused by neurological and orthopaedic anomalies require life-long management.

The general surgeon or paediatrician who does not specialize in the treatment of spina bifida will seldom care for these patients beyond initial diagnosis. For patients presenting with incidental spina bifida occulta and no stigmata indicative of tethered cord syndrome, reassurance is reasonable. Patients presenting with neurological complaints referable to the spine or spinal cord at any age, such as pain, weakness, gait difficulties, or bladder/bowel changes, require radiographic screening and appropriate referral if any spinal dysraphic lesion is suspected. Children born with midline dorsal skin defects, palpable subcutaneous lipomas, or myelomeningoceles are easily screened and clearly require specialized investigation and treatment.

Spina bifida is a common anomaly that encompasses a wide spectrum of clinical disease. The aetiology of and risk factors associated with spina bifida are poorly understood. Three separate entities can be defined: (1) bony abnormalities of the spine without neurological involvement, (2) entities which cause tethered cord syndrome, and (3) myelomeningoceles communicating with the skin. Patients can have no symptoms, may present with pain or weakness related to a tethered cord, or may have absence of neurological function caudal to a myelomeningocele. Prompt diagnosis of spina bifida patients and appropriate referral allow entry into a treatment system which predicts high quality of life for many of the most severely disabled.

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