Encephalocele

Encephalocele is a potentially dangerous, rare birth defect that prevents the neural tube from fully closing.The neural tube is responsible for forming the baby’s skull by closing it completely to form the brain and spinal cord, this process happens during pregnancy. For babies with encephalocele, this tube does not close properly, leading to brain tissue (sac) protruding through the opening gap.¹

The most common area for encephaloceles to occur is at the back of the head. However, it can also develop in other areas of the skull and face, including the top of the head, or between the forehead and nose (frontal).² 

Epidemiology

• The average incidence of around 0.8 to 4 per 10,000 births² 
• For all Neural Tube Defects (NTDs), meningocele, anencephaly, myelomeningocele, and encephalocele make up 80% of all recorded cases; encephalocele accounts for 15-20% of those cases¹
• Encephalocele prevalence rates are suggested to be higher than current statistics, due to pregnancy termination after prenatal screening¹
• Prevalence varies based on geographical area; those in ‘low-resource’ countries have a higher encephalocele rate including countries in South East Asia or Africa¹
• It has been reported that females with encephalocele are more likely to have it at the back of their head (occipital), whereas males are more likely to have it at the front (sincipital)⁴
• The most common location of encephalocele depends on the geographical location. For instance, those in the Western regions are more likely to have it in the back, whilst those in Southeast Asia regions are more likely to have it at the front⁴  

Aetiology

Most cases of encephalocele are congenital, meaning that they arise during pregnancy when the neural tube fails to close completely, preventing proper skull formation. In a smaller number of cases, the condition may result from factors like tumours, trauma, and iatrogenic injury(harm/injury caused by medical treatment or intervention, rather than the underlying disease itself). Genetic, infectious, and environmental factors can also play a role. Infections such as rubella (Rubivirus rubellae) or human herpesvirus type 1 and 2 have been associated with some cases. Additionally, individuals with a history of one or more pregnancies affected by an NTD may have an increased risk of their baby developing encephalocele. Encephalocele can also occur randomly.¹ 

Cognitive outcomes

Encephaloceles can sometimes impact cognitive function, though not in every case, and the severity varies depending on the person. The extent of cognitive issues often depends on the size of the sac, location and amount of brain tissue protruding, as well as any related brain damage resulting from its development, either short-term or long-term. There are four main types of encephaloceles, which are classified according to the location of the sac:³

• Occipital: Back of the head
• Sincipital: Front of the head
• Basal: Near the nasal or forehead area
• Convexity: Side or top of the head

Developmental delay

Encephalocele has been linked to developmental delays, though the severity varies depending on the encephalocele itself and any associated brain damage, meaning the impact is different for each individual.

A study evaluating the long-term developmental delays in cases of cephaloceles found 85 cases, including 48 boys and 37 girls. Among these, 68 were encephaloceles and 17 were meningoceles:⁵ 

Another cognitive outcome associated with encephalocele in children is intellectual disability. While some children with encephaloceles exhibit normal intellectual development and perform at the same educational level as their peers, others may experience mild to severe intellectual impairments. These are often referred to as long-term complications of encephaloceles, often indicating persistent challenges that the individual may face throughout their life. Developmental delays, intellectual disabilities, or any kind of cognitive impairment are more commonly observed in children with larger encephaloceles. This is due to the encephalocele containing a greater amount of brain tissue, which can affect certain areas of the brain that are responsible for cognitive function. Furthermore, increased tissue damage correlates with a greater likelihood of cognitive impairments.¹ 

Neurological issues

Hydrocephalus is a condition that occurs when there is an excess of cerebrospinal fluid (CSF) in the brain, specifically in the ventricles. This buildup can damage brain tissue, leading to several neurological issues, including dementia or physical disabilities. Hydrocephalus has a well-documented association with occipital encephaloceles, occurring in an estimated 60-90% of affected individuals One study examined 17 children (10 girls and 7 boys) with both occipital encephaloceles and hydrocephalus. The diagnosis of hydrocephalus was based on their abnormally large head circumference combined with an enlarged ventricular size on imaging. The researchers reported that the average age at the time of surgery ranged from birth to 15 months. They also observed the following findings:⁶ 

They concluded that occipital encephalocele frequently leads to the development of hydrocephalus, and stated that children who have occipital encephalocele and hydrocephalus tend to have poorer outcomes, which should be considered during prenatal and neonatal counselling.⁶ 

Another retrospective analysis study examined 70 children with encephaloceles between 1994-2012. They observed the following findings:⁷

Neurological outcomes

The neurological impact of encephaloceles varies greatly, with specific outcomes determined by the size and location of the encephalocele, as well as the amount of brain tissue it contains.

Seizures

While not all encephaloceles lead to seizures, epileptogenic encephaloceles, which are often located in the temporal lobe, are recognised as lesional causes of focal epilepsy.⁸ However, research examining the link between seizures and encephaloceles has produced mixed findings. One study investigating temporal encephaloceles and epileptiform activity concluded that these lesions are not a frequent cause of seizures, but also noted that encephaloceles can be difficult to detect on standard scans like brain imaging, which means they may be overlooked during the initial evaluation of seizure aetiology. In cases where seizures are resistant to medication, healthcare professionals should consider the possibility of a temporal lobe encephalocele. When identified, surgical removal of the epileptogenic tissue along with repair of the skull base defect in the temporal lobe may provide a permanent solution to these seizures.⁹ 

The exact prevalence of seizures for individuals with encephalocele varies. A retrospective analysis was implemented to examine the incidence of seizures in affected patients and found that out of the 102 cases included in the analysis, 25.5% (26 patients) experienced seizures.10 Research claims that this may be due to scarring and irritation of brain tissue contained within the encephalocele. A barrier for these individuals to receive timely care and treatment often relates back to it being hard to detect via brain scans, meaning healthcare professionals don’t suspect related encephaloceles right away. It might often be misinterpreted as something that looks normal or be mistaken for a different pathology, causing seizures to persist or worsen over time. In some cases, encephalocele is not found until during brain surgery.¹¹ Related research claims that 17% of those who have occipital encephalocele suffer from seizures and state that it is uncommon in basal and sincipital encephalocele.¹ 

Motor deficits

Children with encephaloceles may also experience motor impairments, the most common being spasticity (muscle spasm), which tends to occur more often in cases of larger occipital encephaloceles that contain a greater amount of brain tissue. Other motor impairments include muscle weakness and coordination difficulties (ataxia). These issues arise because the exposed brain tissue within the encephalocele can affect the underlying structures of the brain that control motor function. The severity of motor deficits is influenced by both the size of the encephalocele and the specific brain structures involved. Larger encephaloceles often result in more severe motor impairment since greater amounts of brain tissue protrude outside the skull. 

This can lead to increased compression in the area and compromise surrounding brain regions, particularly those responsible for motor control.¹ 

Vision and hearing impairments

Vision impairments or loss are commonly seen in basal encephaloceles due to facial defects near the nose and forehead region. It is more common in basal encephaloceles due to it affecting the optic system.¹ 

Encephalocele can also result in hearing problems; for instance, temporal lobe encephaloceles are frequently linked to hearing loss.¹² The ear contains air-filled spaces that help transmit sound, but also create pockets for other tissue toexpand if the surrounding bone barrier is weak. The bone that separates the brain from the ear is covered by a protective membrane called the dura mater, which holds cerebrospinal fluid (CSF). In a way, this fluid helps cushion the brain and is maintained under constant pressure. Constant CSF pressure can push brain tissue into areas of weakened bone, forming an encephalocele, which is essentially a hernia of the brain tissue. Although the bulging area of the brain itself is usually not damaged, the actual problem arises when the encephalocele stretches the dura to the point of tearing, which results in CSF leaking into the ear. In addition, the protruding brain tissue can press on the ear’s structure, which causes hearing loss and the feeling of constant pressure.¹³ 

Summary

Encephalocele is a congenital condition that occurs when a sac containing brain tissue and cerebrospinal fluid protrudes through an opening in the skull. There are four types of encephalocele, which are diagnosed based on their location: occipital (back of the head), sincipital (front of the head), basal (nose or forehead area), and convexity (side of the head). This condition can cause cognitive and neurological complications, and the severity of these complications depends on the size of the encephalocele, the volume of brain tissue involved, and the affected brain area. Larger encephaloceles are associated with a higher likelihood of moderate to severe cognitive or neurological complications, including intellectual and developmental delays, hydrocephalus, seizures, and difficulties with motor functions. Timely care and treatment, such as surgery, is extremely important when it comes to encephalocele to avoid long-term complications and to improve the child’s overall quality of life.