Spina bifida is a type of neural tube defect that results from failure of neural tube closure during the first month in utero. The vertebral bodies develop from the mesoderm around the notochord. From the centre of each body extend two projections which grow around the neural canal to form the vertebral arch. The two halves of the arch fuse in the thoracic region, from where the fusion extends up and down. Failure of fusion of these arches gives rise to spina bifida. It is often associated with maldevelopment of the spinal cord and the membranes.
The history of spina bifida ran into centuries. The foremost description of spina bifida dated back to 1587 by Peter Van Forest who subsequently carried out the first reported surgical procedure of meningomyelocele sac ligation. However, Nicholas Tult noted spina bifida occulta as a congenital developmental defect. Subsequently the term 'spina bifida occulta was coined by Virchow in 1875 on his evaluation of a case of spina bifida concealed under the skin. This brings to mind, the broad classification of spina bifida into spina bifida occulta (SBO) and spina bifida aperta (spina bifida cystica). The distinction is not farfetched. As the later has a visible protusion of spinal cord and/or meninges via a defect in the spine. However our scope is limited to spina bifida occulta. The defect varies in severity from a mere failure of fusion of the spinous processes, to a bony defect with a major aberration in the development of the neural elements.
Spina bifida occulta is the mildest and the commonest. In this, the failure of the vertebral arches to fuse results in bifid spinous processes of vertebrae. This is common in the lumbo-sacral spine, being the commonest site. Externally, the skin may be normal or there may be tell tale signs in the form of a dimple in the skin, a lipomatous mass, a dermal sinus or a tuft of hair.
Neurological impairment is not related to the severity of the bone defect. The commonest manifestation of neurological involvement is a muscle imbalance in the lower limbs with selective muscle wasting. This leads to foot deformities because of muscle imbalance; common ones being equinovarus or cavus. The cause of neural impairment may be: tethering of the cord to the undersurface of the skin by a fibrous membrane (membrana reuniens), tethering of the cord to the filum terminale, bifid cord, transfixed with an antero-posterior bone bar and defective neural development (myelodysplasia).
A symptomless patient, where the lesion is detected on an X-ray taken for some other problem, needs no treatment. Cases presenting with backache respond to physiotherapy. Cases presenting with a neurological deficit need to be evaluated regarding the cause and likelihood of worsening of the neurological deficit. MRI is the imaging modality of choice. Surgical treatment may be required in some cases.
Spina bifida aperta is a developmental defect involves not only the vertebral arches but also the overlying soft tissues, skin, and often the meninges. In severe cases, the nerve tube itself may be exposed. The dorso-lumbar spine is affected most commonly. There is a variable structural defect of closure of the embryonal neural tube giving rise to meningocele which is the protrusion of meninges through a defect in the neural arch. This contains only CSF, meningomyelocele is the protrusion of the meninges along with some neural elements (normally developed spinal cord or cauda equina), the central canal of the cord is dilated (syringomyelia), and the cord lies within the protruded meningeal sac together with the nerves arising from it this is called syringomyelocele and myelocele results from an arrest in the development at the time of closure of the neural groove. An elliptical raw surface, representing the ununited groove is seen. At the upper end of this surface opens the central canal through which CSF may be seen leaking. With the exception of spina bifida occulta, myelocele is the commonest type of spina bifida; though many of these cases are stillborn. If the child is born alive, death ensues within a few days from infection of the cord and meninges.
There may be mild to severe paralysis of the lower limbs. These children are often born with deformities, particularly flexion-adduction contracture of the hip, and deformities of the foot. These deformities are the direct result of muscle imbalance due to paralysis. There may be urinary and bowel incontinence. Treatment of this condition consists of, treatments of the basic defect, orthopaedic treatment to prevent and correct the deformities, and to use the residual motor power in the best possible way; and urological treatment for bladder incontinence.