Encephaloceles Health Article

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.