Definition
Spina bifida is a congenital malformation caused by a disorder of the so-called neural tube during fetal development. The neural tube usually closes towards the spinal canal. This occurs in the third to fourth week of pregnancy. If this closure remains, spina bifida results.
Synonyms in a broader sense
Open spine, open back, spinal cord
Occurrence (Epidemiology)
Defects of the neural tube during development in the womb are the most common malformations of the nervous system. In Germany, this applies to about one in 1000 pregnancies. Due to better prevention of pregnancies, the incidence (occurrence) has decreased significantly.
Causes of spina bifida
How exactly the defect of the neural tube originates is still unclear today. Environmental factors as well as a lack of supply of folic acid to the fetus seem to play a major role. In the third and fourth week of pregnancy, the mother’s folic acid deficiency has a great influence on the development of the spinal canal of the fetus.
Normally, the parts of the vertebral arches fuse together and form the spinal canal. The spinal cord lies here protected by meninges in the spinal fluid. In spina bifida, this channel is not completely closed, since one or more vertebral arches do not close at one point. The spinal cord can now emerge from this gap together with the cerebrospinal fluid.
Forms of spina bifida
There are two forms of spina bifida: In the form of spina bifida occulta, there is only a defect in the bony structures around the spinal cord, i.e. the vertebrae. The vertebral arches are not closed. This form of spina bifida is usually asymptomatic.
The malformation is only noticed on X-ray. Symptoms are only present if the malformation also affects the spinal cord. A so-called dermal sinus (pilonidal sinus) is often associated with spina bifida occulta.
This is a small channel that begins at the surface of the skin and ends either inside or outside the spinal cord. It appears as a pore and is usually more hairy than its surroundings. If the sinus is connected to the spinal cord, meningitis can often occur.
This is a serious complication at any age. The spina bifida cystica is not only the bony mantle surrounding the spinal cord that is malformed, but the spinal cord itself is also affected. Through the gap formed by the unsealed vertebral arches, the membranes of the spinal cord bulge out.
The region of the lumbar (lumbar vertebrae) and sacral (sacral vertebrae) vertebrae is often affected. Roughly speaking, these vertebral groups are located between and above the pelvic bones. The protrusions created here are filled with neural fluid and can be distinguished according to their content.
There are forms in which only the spinal fluid is contained. Other forms of these cysts contain additional spinal cord tissue and nerve roots. Cysts are fluid-filled cavities.
In the worst case, an entire part of the spinal cord bulges out of the gap.
- Spina bifida occulta (closed concealed spina bifida)
- Spina bifida cystica (cystic spina bifida)
Spina bifida aperta (“obvious” spina bifida; also known as spina bifida cystica) is a final disorder of the bony vertebral arch. This means that the posterior part of a vertebral body, the so-called vertebral arch, is not or only partially present.
This part is normally intended to protect the spinal cord, which lies within the vertebral arch. Due to the final disorder, the spinal cord has lost its bony protection. In contrast to spina bifida occulta, in spina bifida aperta, the meninges (meninges, synonymous with spinal cord membranes) and possibly also the spinal cord are not in the right place, but bulge outwards.
As a result, the skin over the site of the defect thins out and bulges outward like a cauliflower. The meninges (meningocele) and possibly also the spinal cord (meningomyeolocele) then lie in this thin sack of skin. The meninges and spinal cord have prolapsed (i.e. are no longer in their original position, but have protruded through the opening in the spinal column), similar to intestinal loops in an inguinal hernia.
Depending on the severity of the hernia, water may also be present in the hernial sac (myelocystocele, myelocystomeningocele). The most severe form is called myeloschisis.Here, the not completely matured spinal cord, called neural plate, lies open at the back without being covered by protective meninges or skin. The spina bifida aperta is usually located in the area of the lower lumbar spine, or in the sacrum.
It is usually accompanied by significantly more severe symptoms than spina bifida occulta, such as paralysis, foot malpositions, sensitivity disorders, lack of control over the bladder and rectum. Hydrocephalus (hydrocephalus) is also more common in spina bifida aperta. Spina bifida occulta (“hidden” spina bifida) also refers to a final disorder of the bony vertebral arch.
Here, too, the spinal cord has lost its bony protection. In contrast to spina bifida aperta, the spinal cord and meninges are not affected by the final disorder, but lie fully developed in the place intended for them. The skin above is also intact.
People with spina bifida occulta often have no symptoms at all and the condition is eventually discovered by chance on an X-ray or similar. As long as no symptoms occur, spina bifida occulta has no further medical significance. In some cases, it can be conspicuous by skin changes such as increased hairiness (hypertrichosis) at the site of the spina bifida occulta or by a dermal sinus.
A dermal sinus is a small duct in the skin that ends blind. A meningo- or myelomeningocele is a spina bifida aperta (also spina bifida cystica). Similar to an inguinal hernia, when the intestine is in a hernia sac, the meninges with (myelomeningocele) or without (meningocele) spinal cord are located in a sac of skin at the site of the spina bifida. Normally, both the skin sack and the meninges are closed so that the very sensitive spinal cord is at least slightly protected. Sometimes, fluid is also stored in the hernial sac, so that one can speak of a cyst.
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