The encephaloceles are the result of the incomplete occlusion of the fetal neural tube. The neural tube is the fetus tissue that will create the brain, the spinal cord as well as the bones that surround them. The result of the incomplete occlusion is to create bone deficits in the facial skeleton and skull from where protruding thin membranes that resemble as a small sac that cover the brain (meninges), the cerebrospinal fluid or/and brain tissue.
Encephaloceles occur at a frequency of about 1/5000 births. In some areas of Southeast Asia, they are more common (especially in the front of the skull).
The exact causes that are responsible for encephalocele are unknown. It is believed that multiple factors are required for the development of an encephalocele including both genetic and environmental factors as well as the nutritional status of the mother (lack of folic acid) and the mother's exposure to teratogenic agents during early in pregnancy. A small percentage, finally, is due to bone defects of the cranial skeleton in cases of craniofacial clefts, or bone loss from infection or injury.
LOCATION & CLASSIFICATION
Most of the encephaloceles are located at the posterior part of the skull (in the base). These encephaloceles have the worst prognosis and often fetus dies before pregnancy is completed. The rest types of encephaloceles that constitute a smaller percentage have much better prognosis, they are located in the inferior part of the skull, and depending on their exact projection, they are characterized as:
- Nasofrontal when projecting between the frontal and nasal bones.
- Naso-Orbital when projecting in the orbit.
- Nasoethmoidal when projecting below the nasal bones (between nasal bones and nasal cartilages).
The size of the encephalocele varies from very small, where in this case it may remain unnoticed, up to very large, with projection of substantial amount of brain tissue.
The prognosis depends on the location, the size of encephalocele as well as the brain malformations that may coexist. In many cases, the brain tissue that projecting is not functional and therefore it can be removed without any problems.
The functional problems that may arise depending on the location and the size of encephalocele. These are the following:
- Hydrocephalus (a condition in which excess cerebrospinal fluid in the skull causes pressure on the brain)
- Neurological problems
- Vision problems
- Growth problems
It may be emphasized, however, that many cases are not accompanied by functional problems and the mental development may be entirely normal.
Encephalocele treatment in most cases is surgery to put the part of the brain that is outside the skull back into place and close the opening. The encephaloceles concerning the posterior part of the skull fall exclusively in the specialty of Neurosurgery, while the anterior encephaloceles require the combination of Neurosurgical and Craniofacial techniques. The surgical rehabilitation is usually performed during the neonatal or infancy period. Some factors such as if the encephalocele is covered by skin or not as well as the general condition of the newborn play a decisive role for the exact time of the surgery. The basic principle of rehabilitation is the excision of the area (part) that is projected and the definitive closure of the deficit, after a detailed assessment of the possible consequences of the excision.
The repair of craniofacial deformity that accompanies each case, may be performed during the initial surgery or if this is not possible, at a second time.