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.
Causes of encephaloceles
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.
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.
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).
Diagnosis of encephaloceles
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.
An ultrasound exam is a routine examination in which reflected sound waves are used to create an image of the developing foetus. 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 (foetal 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.
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.