Neurological Diseases: Spina Bifida

Introduction

Spina bifida is a congenital abnormality (present at birth) and results from the defective closure of neural tube.

Neural tube is a tube like structure from which the central nervous system (brain & spinal cord) develop during the embryonic & fetal development.

There are several types of neural tube defects and spina-bifida is one among them and occurs when the caudal end of the neural tube doesn’t close properly. This causes the posterior elements of vertebrae (the lower spine) not formed properly and a gap exists.

Classification/Types

There are mainly 2 types;

1) Spina-bifida occulta
2) Spina-bifida Cystica

In the 1st type which is also the commonest type there is just a vertebral bone defect but no meninges (coverings of spinal cord) or spinal cord /spinal nerve roots come out through it. This is the mildest form with the best prognosis. In fact majority of the patients are not even aware that they have got it. It is many times found incidentally during radiological work up on the lower back area.

In the 2nd type there are two subtypes; meningocele & myelomeningocle. Meningocele happens when the meninges alone protrude through the spina-bifida bone defect. Myeomeningocele happens when the meninges and spinal cord elements both protrude out through the defect. This is the most serious type.

Patients with myelomeningocele may also have chiari type 2 malformation where the lower end of cerebellum (the cerebellar tonsils) herniated to the spinal canal. These patients may also have hydrocephalus.

What causes spina-bifida?

This results due to certain damage occurring to the neural tube during the embryonic stage of development. It is thought to be related to genetic and/or environmental factors. For example using anticonvulsant like valproate has been found to be associated with increased risk of neural tube defects.

How does patient present?

Spina bifida-occulta may go unnoticed since majority of these patients are asymptomatic. However all these patients may have a skin dimple or a tuft of hair or a lipoma corresponding to this defect.

Patients with spina bifia cystica will present with a cystic swelling in the lower back. Patients with the severe form, the myelomeningocele, will also present with leg weakness, bowel/bladder disturbances, decreased sensory perception in the legs secondary to a cauda equina or conus medullaris syndrome.

Additional manifestations related with chiari type 2 and hydrocephalus may be seen with myelomeningocele.

Diagnosis

The following investigations are usually necessary;

• Radiological study of the spine (x-ray, CT or MRI; MRI is the best)
• EMG/NCS (electromyography and nerve conduction study)
• CT or MRI of brain etc

Treatment

Spina bifida occulta patients do not require any treatment,

The spin bifida cystica patients generally require surgical interventions of the lower spine area.

Otherwise treatment is essentially symptomatic and supportive that includes physical therapy, treatment of bladder infections etc.

The neural tube defects can be prevented to some extent by giving pregnant women with folic acid. And this is especially important for those who are on anticonvulsants during pregnancy.

Ultrasound and AFP (alpha fetoprotein) tests can detect these conditions in the intrauterine stage itself so giving an option of medical termination of pregnancy or now-a-days even intrauterine surgical options.

Neurologist, neurosurgeon and orthopedic surgeon are the specialists usually involved in the care of these patients.



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