Encephaloceles

Definition

Encephaloceles refers to defects in the development of a fetal structure called the neural tube. The tube fails to close completely during development of the fetus, resulting in portions of the brain and its surrounding membranes that protrude from the skull in sac-like formations. Often, normal brain function is impaired and children with encephaloceles experience delays in development.

Description

In normal fetal development, the neural tube forms by the closure of the neural structure. When this does not occur in the case of an encephalocele, the result is a groove. The groove can form down the middle region of the upper part of the skull, or between the forehead and the nose, or down the back of the skull. The incomplete closure also creates areas where the brain and its overlaying membrane can bulge outward in sac-like protrusions. The larger deformities, in particular those that occur at the back of the skull, are readily evident and are recognized very soon after birth. These deformities are also associated with abnormal structure and functioning of the brain. Some encephaloceles are less evident, even to the point of being undetectable at birth. Defects in the region of the forehead and nose are examples.

Demographics

Encephaloceles occur rarely. At a rate of one per 5,000–10,000 live births, an encephalocele is less common than spina bifida , another neural tube defect. Geographical differences occur with respect to the type of encephalocele. Malformation of the back portion of the head is more common in Europe and North America, whereas involvement of the front portion of the head occurs more frequently in Southeast Asia, Malaysia, and Russia.

Causes and symptoms

The exact cause of encephaloceles is not yet known. The disorder is passed on from generation to generation, and is more prevalent in families where there is a history of spina bifida. It is clear that one or more genetic abnormalities lie at the heart of the condition. However, fetal development is an extremely complex process, with interactions between various genes, and influence of the external environment determining which genes are activated at which time. Thus, pinning down the crucial genes whose expression or changed activity produces abnormal neural tube formation is a difficult task.

Research using animal models has shown that teratogens, compounds like x rays, trypan blue, and arsenic, which can damage the developing fetus, cause encephaloceles in the animals. Whether exposure of a human fetus to such agents contributes to encephalocele formation in humans is not known.

Most often, the symptoms of encephaloceles are not difficult to recognize. These include the excessive build-up of cerebrospinal fluid in the brain (a condition called hydrocephalus ), paralyzed arms and legs (spastic quadriplegia), an abnormally small head (microcephaly ), difficulty in tasks like walking and reaching because of a lack of coordination (ataxia ), delayed or impaired mental and physical development (although intelligence is not always affected), problems with vision, and seizures .

If the bulging portion contains only cerebrospinal fluid and the overlaying membrane, the malady can also be called a cranial meningocele or a meningocele. If brain tissue is also present, the malady can also be referred to as an encephalomeningocele.

Diagnosis

Diagnosis is based at the discovery of the physical abnormalities at birth or sometime later, and on the failure to attain the various physical and mental developmental milestones that are a normal part of early life.

Treatment team

Medical treatment involves family physicians, neurosurgeons, and nurses. Special education professionals, physical therapists, and caregivers are also an important part of the treatment team, as an affected person may require assistance in everyday activities throughout life.

Treatment

Treatment typically involves surgery. The surgery is usually accomplished soon after birth, and re-positions the bulging brain back into the skull, removes any of the sac-like protrusions, and corrects the skull deformities. Often, shunts are placed during surgery to drain excess cerebrospinal fluid from the brain. While delicate, the operation typically relieves the pressure that would otherwise impede normal brain development. Other treatment involves dealing with specific symptoms and producing as comfortable and satisfying everyday life as is possible.

Recovery and rehabilitation

Prospects for recovery are difficult to predict prior to surgery. Nonetheless, if surgery is successful, and other developmental difficulties have not occurred, an individual can develop normally. Where neurological and developmental damage has occurred, the focus shifts from recovery to maximizing mental and physical abilities.

Clinical trials

As of April 2004, no clinical trails for specific study of encephaloceles were being conducted. However, research is underway to more clearly define the mechanisms of brain development, and several clinical trials related to neural tube defects are recruiting participants. Updated information can be found at the National Institutes of Health clinical trials website at: http://clinicaltrials.gov.

Prognosis

As for recovery and rehabilitation, the prognosis is varies and cannot be predicted beforehand. In general, when the bulging material consists of mainly cerebrospinal fluid, a complete recovery can occur 60–80% of the time. However, the presence of brain tissue in the protruding material can reduce the chances of a complete recovery considerably.

Special concerns

Folic acid, a B vitamin, has been shown to help prevent neural tube defects when taken before and in early pregnancy. The March of Dimes organization and the United States Public Health Service recommend that all women who may become pregnant take a multi-vitamin that contains 400 micrograms of folic acid every day.

Resources

BOOKS

McComb, G. G., ed. Neural Tube Defects. American Association of Neurological Surgeons, 1998.

PERIODICALS

"Beaumont surgeons correct rare defect for Caribbean boy." Health Week (July 1, 2002): 17.

OTHER

NINDS Encephaloceles Information Page. National Institute of Neurological Disorders and Stroke. (April 7, 2004). <http://www.ninds.nih.gov/health_and_medical/disorders/encephaloceles.htm>

Prevention of Neural Tube Defects. The Arc. (April 10, 2004). <http://www.thearc.org/faqs/folicqa.html>

ORGANIZATIONS

Birth Defect Research for Children. 930 Woodcock Road, Suite 225. Orlando, FL 22808. (407) 895-0802 or (800) 313-2232; Fax: (407) 895-0824.

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Avenue, White Plains, NY 10605. (914) 428-7100 or (888) 663-4637; Fax: (914) 428-8203. askus@ marchofdimes.com. <http://www.marchofdimes.com>.

National Institute for Neurological Diseases and Stroke (NINDS). 6001 Executive Boulevard, Bethesda, MD, 20892. (301) 496-5751 or (800) 352-9424. <http://www.ninds.nih.gov>.

National Organization for Rare Disorders. 55 Kenosia Avenue, Danbury, CT 06813-1968. (203) 744-0100 or (800) 999-6673; Fax: (203) 798-2291. [email protected]. <http://www.rarediseases.org>.

Brian Douglas Hoyle, PhD