Encephalocele
Background
An encephalocele is a very rare congenital defect in which nervous tissue protrudes through openings in the skull, resulting in a skin covered sac outside the skull. Less frequently, the sac may be covered only by a membrane, increasing its vulnerability. The contents of the sac can vary, and may include meninges (the membranes that surround the central nervous system), blood vessels, and neural tissue from the underlying area of the brain. The prognosis for this condition depends upon the location of the sac and its contents, with the outlook being most favorable when no functional neural tissue is contained in the sac.
Causes
During fetal development, the central nervous system develops from a precursor called the neural tube. This tube is formed when folds along the back of the embryo become elevated and eventually meet and coalesce to form a hollow canal, which is the future home of the spinal cord and brain. Improper closure of the neural tube may result in a groove down the midline of the upper, lower, or frontal part of the skull. Encephalocele results if the brain begins to grow through these openings.
There is a genetic component of this condition, as it is sometimes generational and also occurs more frequently in families with a history of neural tube defects, such as spina bifida. However, the interplay of genetic and developmental variations that combine to produce this condition is not fully understood.
Risk Factors
- a family history of spina bifida or anencephaly (other defects of the neural tube)
- folic acid deficiency may contribute to neural tube defects.
Symptoms
In most cases encephaloceles can be detected during gestation by ultrasound imaging and present as dramatic deformities visible at birth. For encephaloceles which are not outwardly apparent, symptoms may include hydrocephalus, cerebrospinal fluid leak, developmental delays, uneven gait and seizures.
Diagnosis
Ultrasound images of the fetus can reveal the presence of a herniated, fluid-filled sac outside the skull. Other developmental anomalies usually accompany encephalocele, so a positive diagnosis should be followed by a search for other conditions or abnormalities, such as hydrocephalus, microcephaly (abnormally small head), paralysis and mental retardation. Encephaloceles that, for whatever reason, go undetected during gestation are usually diagnosed at birth by observation of the deformity.
In rare cases, a small encephalocele in the nasal cavity can remain undetected for years, even into adulthood.
An MRI is the preferred test to identify the contents of the encephalocele, which is essential for determining the best treatment process.
Treatment
Surgery to remove the herniated tissue and repair the opening in the skull is the only treatment. If the encephalocele is covered by normal skin rather than a thin membrane, surgery may be postponed until the child is older. In most cases, any neural tissue contained in the sac is abnormal and is removed. However, if healthy neural tissue is present in the sac, one of the goals of surgery is to preserve it.
The surgical approach depends upon the location and contents of the encephalocele. If the sac does not contain vital nervous tissue, the encephalocele is simply removed and the opening in the skull is repaired. In cases that do involve functional nervous tissue, a craniotomy is usually performed, whereby the affected area of the skull is further opened so as to place the external tissue inside.
Encephaloceles of the skull base can be directly approached through expanded endonasal approach (EEA). This state-of-the-art, minimally invasive surgical procedure uses the nose as a natural corridor to reach these lesions. There are no incisions in the skin of the face or head.
Prevention
The exact causes of this condition are not fully understood, so there are currently no guidelines for prevention. Some studies have shown that taking folic acid supplements in the early weeks of pregnancy may reduce likelihood of neural tube defects by as much as 50 percent.