Introduction

Encephalocele is a congenital neural tube defect (NTD) in which intracranial contents such as the brain, meninges, and ventricles prolapse through a skull defect.¹ The brain and spinal cord are developed from the neural tube. It is created by the neural plate folding upward early in pregnancy, which is followed by the opposite side of the neural tube closing. Neural tube abnormalities resulting from incomplete closure are fatal, with the exception of milder cases of spina bifida.² Most encephaloceles are congenital, with a smaller proportion acquired due to trauma, tumours, or injury. The incidence of inherited encephalocele is one in 10,000 live births; however, the true incidence may be higher due to termination of pregnancy after prenatal diagnosis.³ Seventy-six per cent of the deaths that occur in encephalocele patients take place within the first day after delivery. Half of the survivors have some form of neurodevelopmental delay.¹ 

Overall, assigned males at birth (AMAB) and assigned females at birth (AFAB) are equally impacted; however, for some encephalocele forms, distinct patterns show up. AFAB are more likely to have occipital (back of the head) encephaloceles. On the other hand, AMAB are slightly more likely to have anterior cranial fossa encephaloceles. The occipital region is where between seventy to ninety per cent of encephaloceles occur, especially in North America and Western Europe. Anterior skull base encephaloceles are more prevalent in Asia, Africa, and Russia, occurring in one out of every 3500–6000 live births. However, these particular illnesses are much less common in North America and Europe, where there is only one case for every 35,000 live births. Encephaloceles are linked to more than 30 syndromes, such as amniotic band syndromes (ABS), Fraser, Walker-Warburg, and Meckel-Gruber syndromes (MKS).³

What are the features of Encephalocele?

Encephalocele is characterised by the protrusion of a sac containing meninges and/or brain tissue outside the skull, known as herniation of intracranial contents. Although the position of a lesion varies, it is most frequently found in the occipital area, where it occurs in around seventy-five per cent of cases. The frontonasal (nose bridge), nasoethmoidal (nose-forehead), parietal (top-rear portion of the skull), frontal (forehead), temporal (base of the skull), and nasopharyngeal (nasal) regions are other less frequently found sites.¹

Syndromes associated with encephalocele?

Meckel-gruber syndrome 

MKS has autosomal recessive inheritance. If the illness has happened before, there is a twenty-five per cent chance that it may repeat in subsequent pregnancies.⁴ It is caused by mutations in genes encoding proteins that are structural or functional components of the primary cilium, which regulates developmental signalling pathways. MKS is characterised by two severely cystic kidneys, polydactyly, and encephalocele, particularly occipital encephalocele.⁵ In addition to the basic triad, MKS can manifest with a variety of additional abnormalities, such as heart problems, cleft lip and palate, abnormalities of the AMAB genitalia, bowing and shortening of the long bones, and hepatic developmental disorders.^{4, 5} Due to pulmonary hypoplasia, MKS is fatal in utero or immediately after birth, though there have been a few documented prolonged survivors.⁴

Walker-warburg syndrome

Walker-Warburg syndrome presents at birth with neurological and developmental impairments, hypotonia, muscle weakness, and seizures. It is linked to congenital muscular dystrophy, cerebellar deformities, hydrocephalus, and abnormalities of the eyes. Brain abnormalities such as hypoplasia of corpus callosum, occipital encephalocele and Dandy-Walker malformation have also been described.⁶

Fraser syndrome

Fraser syndrome is an uncommon condition that has autosomal recessive inheritance. The prominent feature is cryptophthalmos, which is also known as a hidden eye. Developmental delay, craniofacial dysmorphism, ear malformations, cleft lip and palate, laryngeal malformation, syndactyly, ambiguous genitalia, renal malformation, and musculoskeletal abnormalities are further characteristics linked to this condition. Meningoencephalocele and spina bifida are common neurological anomalies associated with Fraser syndrome. Less commonly reported abnormalities include hydrocephalus, encephaloceles, mild cerebellar hypoplasia, and periventricular leukomalacia.⁷

Amniotic band syndrome

In rare cases, encephaloceles are linked to ABS, which is best described as many secondary abnormalities that are caused by the development of thin membrane bands during pregnancy. ABS-related encephaloceles may have multiple locations. Asymmetry and nasal deformity are the most common craniofacial abnormalities linked to ABS. Unlike normal encephaloceles, those associated with ABS might only have meninges covering them instead of skin. The additional tissue may differently influence cranial skeleton development, the lesion must be corrected to permit normal brain growth and development.⁸

Diagnosis

Prenatal diagnosis

It is possible to do genetic testing for chromosomal abnormalities as early as week ten of pregnancy. However, abnormal ultrasound results may be found in approximately three per cent of patients who have a negative screening test. Around eight per cent of cell-free DNA screenings of maternal plasma samples may miss chromosomal abnormalities.³ One of the main techniques for prenatal detection is abdominal ultrasound. When ultrasound results are unclear or imaging is restricted due to a severe shortage of amniotic fluid, fetal magnetic resonance imaging is used. A reliable diagnosis of abnormalities of the central nervous system can be made due to better soft-tissue resolution, which produces more detail of intracranial structures. Usually, it is done after eighteen weeks of pregnancy.⁵

Postnatal diagnosis

The visible sac of the encephalocele and any related limb or craniofacial abnormalities might be seen during a physical examination. Abdominal and cranial ultrasonography are examples of postnatal imaging that can provide more information about brain abnormalities and the involvement of abdominal organs.⁴

Management

Surgery is used to treat encephaloceles. The main objectives of surgery for encephaloceles are to remove nonfunctioning brain tissue, fix the bony defect, close the membrane securely, and remove excess skin. To prevent postoperative cerebrospinal fluid (CSF) leaks, intraoperative lumbar drainage is frequently used for five to seven days. Although they can occur in as many as six per cent of instances, postoperative CSF leaks usually go away after lumbar drainage. In approximately one to two per cent of instances, further investigation is required for chronic CSF leakage. Significant facial skeleton remodelling may naturally develop over time in cases of anterior encephaloceles removed during infancy or early childhood. However, in difficult situations with severe craniofacial malformations, reconstruction could be necessary to restore function and appearance.³ Hydrocephalus is a common and accompanying condition in patients with encephalocele. To improve prognosis results, hydrocephalus must be well-managed.¹

Outcomes

Encephalocele is a serious condition with significant risks of morbidity and mortality.¹ About half of patients who survive beyond the first day of life experience some degree of neurodevelopmental delay and cognitive deficits. Neurological issues include hydrocephalus, spasticity, apathy, paraplegia and seizures. Poor prognostic factors include a sac diameter greater than five cm, the presence of encephalocele with functional neural tissue, and the presence of additional abnormalities such as hydrocephalus. Good prognosis indicators include a dysplastic sac, meningocele (containing only meninges), a sac diameter of less than five cm, the lack of other abnormalities, and normal ventricles.¹ 

Evaluations of children with encephaloceles over an extended period of time have revealed that eleven per cent had mild impairment, 16 per cent had moderate impairment, 25 per cent had severe impairment, and 48 per cent had appropriate development. The prognosis for occipital encephaloceles is poorer than that of frontal encephaloceles because of the higher incidence of seizures and hydrocephalus. About half of the people who have occipital encephalocele are unable to live independently in society. Seventy-one per cent of patients survive to one year, and sixty-seven per cent live to twenty.³ When encephalocele is part of a severe syndrome such as MKS, the condition is often lethal either in utero or immediately after birth.⁵ 

Summary

Encephalocele is a congenital neural tube defect where brain tissue, meninges, and sometimes ventricles herniate through a skull defect. They most commonly occur in the occipital region; however, there are multiple locations. The condition carries high mortality, with most deaths occurring within the first day of life, and survivors often face neurodevelopmental delays and neurological complications such as hydrocephalus and seizures. Encephaloceles may occur alone or as part of syndromes such as MKS. There are over 30 syndromes associated with encephalocele, including Walker-Warburg, Fraser, and ABS. Diagnosis relies on prenatal ultrasound, fetal MRI, and genetic testing, while postnatal evaluation involves clinical and imaging assessment. The treatment for encephalocele is surgical, and the prognosis is dependent on the size, contents, as well as associated abnormalities.