Encephaloceles are rare birth defects associated with skull defects characterized by partial lacking of bone fusion leaving a gap through which a portion of the brain sticks out (protrudes). In some cases, cerebrospinal fluid or the membranes that cover the brain (meninges) may also protrude through this gap. The portion of the brain that sticks outside the skull is usually covered by skin or a thin membrane so that the defect resembles a small sac. Protruding tissue may be located on any part of the head, but most often affects the back of the skull (occipital area). Most encephaloceles are large and significant birth defects that are diagnosed before birth. However, in extremely rare cases, some encephaloceles may be small and go unnoticed. The exact cause of encephaloceles is unknown, but most likely the disorder results from the combination of several factors (multifactorial).
Encephaloceles are classified as neural tube defects. The neural tube is a narrow channel in the developing fetus that allows the brain and spinal cord to develop. The neural tube folds and closes early during pregnancy (third or fourth week) to complete the formation of the brain and spinal cord. A neural tube defect occurs when the neural tube does not close completely, which can occur anywhere along the head, neck or spine. The lack of proper closing of the neural tube can lead to a herniation process which appears as a pedunculated (having a stalk-like base) or sessile (attached directly to its base without a stalk) cystic lesion protruding through a defect in the cranial vault referred as encephalocele. They may contain herniated meninges and brain tissue (encephalocele or meningoencephalocele) or only meninges (cranial meningocele). Encephaloceles containing tissue from the brain and spinal cord are called encephalomyeloceles.
The symptoms of an encephalocele can vary from one individual to another depending upon many different factors including size, location and the amount and kind of brain tissue protruding from the skull. Encephaloceles are congenital malformations i.e. present at birth. The location of the encephaloceles is very important since there are distinct clinical implications for treatment and prognosis for anterior and posterior encephaloceles. Posterior encephaloceles are more often associated with neurological problems. Encephaloceles toward the front of the skull usually do not contain brain tissue and generally have a better prognosis.
Most registries and epidemiological studies classify encephaloceles using broad categories like frontal, parietal, occipital and sphenoidal.
The most common area of skull for the development of an encephalocele is the upper portion from the forehead to the lower back of the skull in the area of the occipital bone. Encephaloceles can also occur near the sinuses, forehead and nose or near the base of the skull.
Symptoms that can develop include delays in reaching developmental milestones, intellectual disability, learning disabilities, growth delays, seizures, vision impairment, uncoordinated voluntary movements (ataxia), and hydrocephalus, a condition in which excess cerebrospinal fluid in the skull causes pressure on the brain. Hydrocephalus can result in a variety of symptoms. Some affected individuals develop microcephaly, a condition that indicates that head circumference is smaller than would be expected for an infant’s age and sex. Also in some cases, affected individuals experience progressive weakness and loss of strength in the arms and legs due to increased muscle tone and stiffness (spastic paraplegia). However it is important to note that not all affected individuals may have the symptoms discussed above and some children may have normal intelligence, while others experience intellectual disability. Parents should talk to their child’s physician and medical team about their specific case, associated symptoms and overall prognosis.
In some cases, encephaloceles occur in association with other neurological conditions such as Dandy-Walker malformation or Chiari malformation. Dandy-Walker malformation is a brain malformation with partial or complete absence of the cerebellar vermis and enlargement of the fourth ventricle. Chiari malformation of the brain is characterized by a downward displacement of the cerebellar tonsils through the opening at the base of the skull (foramen magnum) which may result in the obstruction of cerebrospinal fluid (CSF) circulation leading sometime to a non-communicating hydrocephalus. (For more information on these disorders, choose the specific disorder name as your search term in the Rare Disease Database.)
According to data from the Metropolitan Atlanta Congenital Defects Program (Siffel et al., 2003), the majority of deaths of children with encephalocele occurred during the first day of life and the estimated survival probability to 20 years of age was 67.3%, In addition, factors associated with increased mortality were low birth weight, presence of multiple defects instead of single defect, and Black or African American ancestry.
The exact underlying cause of an encephalocele is unknown. Most cases occur sporadically. Most researchers believe that multiple factors are required for the development of an encephalocele including both genetic and environmental factors.
Encephaloceles are more common in individuals who have a family history of neural tube defects such as spina bifida or anencephaly. In such cases, individuals might have a genetic predisposition to developing a neural tube defect and may develop an encephalocele. A person who is genetically predisposed to certain disorders may carry a gene (or genes) for the disease, which may not necessarily be expressed unless it is triggered or “activated” under certain circumstances, such as the exposure to particular environmental factors.
No specific environmental factors have been confirmed as contributing to the development of an encephalocele. Researchers speculate that certain toxins or infections may be involved.
An encephalocele may occur as part of more than 30 different syndromes, including Meckel syndrome, Fraser syndrome, Roberts syndrome, and Walker-Warburg syndrome. Amniotic band syndrome can also be associated with an encephalocele.
The Centers for Disease Control and Prevention (CDC) estimates that approximately 375 babies are born each year in the United States with an encephalocele. That would be approximately 1 in 10,000 babies each year. Females are more likely to have an encephalocele in the back (occipital area) of the skull, while males are more likely to have one in the front of the skull. In Western populations, encephaloceles are more common in the back of the skull. In Southeast Asia, they are more common in the front of the skull.
Most encephaloceles are diagnosed on a routine prenatal ultrasound or seen right away when a baby is born. In some cases, small encephaloceles may initially go unnoticed. These encephaloceles are usually located near the baby's nose or forehead.
Clinical Testing and Work-Up
An ultrasound exam is a routine examination in which reflected sound waves are used to create an image of the developing fetus. An encephalocele may appear as a cyst on an ultrasound examination. If an encephalocele is diagnosed prenatally, further tests may be recommended to detect whether additional anomalies are present. Such tests can include a prenatal magnetic resonance imaging (fetal MRI).
Surgical intervention is usually necessary for children with an encephalocele. Surgery is usually performed sometime between birth and 4 months of age depending upon the size, location and associated complications as well as whether a layer of skin covers the encephalocele. If a layer of skin is present and acts as a protective cover, surgery can be delayed for a few months. If no layer of skin protects an encephalocele, surgery might be recommended shortly after birth.
Surgery is done to put the protruding contents of an encephalocele back into the skull. The neurosurgeon will cut and remove a portion of the skull (craniotomy), allowing access to the brain. Then, a neurosurgeon will cut through the dura mater, the tough outer covering of the brain.
Next, the neurosurgeon will relocate any herniated portion of the brain, meninges and fluid back into the skull and will remove the surrounding sac. Afterward, the dura mater is closed and the skull is repaired either by replacing the piece of the skull that was initially removed or using an artificial replacement. Surgical correction of an encephalocele can be achieved without causing any further functional disability, even in cases of large encephaloceles.
Additional treatment is based on the specific symptoms present in each individual case. Craniofacial abnormalities or additional abnormalities of the skull are treated surgically. Hydrocephalus may be treated by surgically implanting a shunt that allows excess cerebrospinal fluid to be drained.
Services that may be beneficial to the patient may include special remedial education, and other medical, social, and/or vocational services. Genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.
Studies have shown that adding folic acid (a form of B vitamin) to the diet of women who might become pregnant can lower the risk of some neural tube defects. The CDC and other health agencies have advocated that women of childbearing age should have 400 micrograms of folic acid daily.
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FROM THE INTERNET
National Institute of Neurological Disorders and Stoke. Encephaloceles Information Page. February 12, 2007. Available at: http://www.ninds.nih.gov/disorders/encephaloceles/encephaloceles.htm Accessed On: October 24, 2011.
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Accessed on: 10/24/2011