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NORD is very grateful to J. Fernando Arena, MD, PhD, FACMG, Medical Officer, Birth Defects Epidemiology Team, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, for the assistance in the preparation of this report.
Synonyms of Encephalocele
- cranium bifidum
- cranial meningocele
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.
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