Introduction

Encephalocele is a rare congenital neural tube defect characterized by the herniation of brain tissue and meninges through a defect in the skull. It occurs due to abnormal closure of the neural tube during embryonic development, typically between the third and fourth weeks of gestation. Although relatively uncommon, encephalocele represents a significant cause of neonatal morbidity and mortality, often associated with neurological deficits, hydrocephalus, and developmental delays.

Understanding the risk factors associated with encephalocele is crucial for both prevention and early detection. Research indicates that its development is multifactorial, involving a complex interplay between genetic predisposition and environmental exposures. Genetic syndromes, chromosomal abnormalities, maternal nutritional deficiencies, and teratogenic agents have all been implicated in its pathogenesis. Identifying these risk factors not only provides insight into the underlying mechanisms of neural tube closure but also supports the development of preventive strategies, such as preconception counseling and folic acid supplementation.¹

Understanding encephalocele

Encephalocele is a neural tube defect (NTD) characterized by the protrusion of brain tissue, meninges, and sometimes cerebrospinal fluid (CSF) through a defect in the skull. This cranial defect usually occurs along the midline, most commonly in the occipital region, although frontal, parietal, and basal encephaloceles have also been reported. The severity of the condition depends on the size and location of the defect, as well as the amount of neural tissue involved.

The global prevalence of encephalocele is estimated at approximately 0.8–4 per 10,000 live births, with significant geographic variation. In some regions, particularly where maternal malnutrition is prevalent, the incidence is higher. Encephaloceles are often associated with other congenital anomalies, such as hydrocephalus, microcephaly, cleft lip/palate, and craniofacial malformations, making early recognition essential for comprehensive management.³

Clinically, infants with encephalocele may present with a visible sac-like protrusion at birth. The contents of the sac may range from meninges alone (cranial meningocele) to brain tissue and ventricles (encephalomeningocele or hydroencephalomeningocele). Associated neurological manifestations can include developmental delays, seizures, motor deficits, and visual or hearing impairments.

Genetic risk factors

Genetic predisposition plays a key role in the development of encephalocele, with both chromosomal abnormalities and single-gene mutations contributing to its occurrence. While most cases are sporadic, a subset is associated with hereditary syndromes, indicating a strong genetic component.

Associated risk factors include:

Chromosomal abnormalities

Encephaloceles have been reported in association with trisomies (such as Trisomy 13 and Trisomy 18) and other chromosomal rearrangements. These anomalies may disrupt genes essential for neural tube closure, leading to skull defects and brain herniation.

Single-gene mutations and syndromic associations

Several genetic syndromes include encephalocele as part of their phenotype:

• Meckel–Gruber syndrome: Characterized by encephalocele, polycystic kidneys, and polydactyly, this autosomal recessive disorder is strongly linked to ciliopathy genes
• Walker–Warburg syndrome: A severe congenital muscular dystrophy presenting with lissencephaly, eye malformations, and encephalocele
• Knobloch syndrome: Associated with occipital encephalocele and retinal detachment, caused by mutations in the COL18A1 gene

Familial clustering and recurrence risk

Although rare, familial recurrence of encephalocele has been observed, suggesting polygenic or multifactorial inheritance. Parents with one affected child have a slightly increased risk of recurrence in future pregnancies, particularly if additional relatives are affected

Candidate genes and ongoing research

Research continues to identify candidate genes involved in neural tube development, including those regulating folate metabolism, cell polarity, and ciliary function. Variants in MTHFR and VANGL genes have been implicated, though their exact contribution to encephalocele risk remains under investigation.⁴

Environmental risk factors

While genetics play a significant role in the development of encephalocele, environmental factors are equally important in influencing risk. These factors often act during the critical period of neural tube closure in early embryogenesis (weeks 3–4 of gestation), either by directly interfering with cellular processes or by modifying gene expression.

Maternal Nutritional Deficiencies

• Folate deficiency: One of the most well-established risk factors for neural tube defects, including encephalocele. Folate is essential for DNA synthesis and methylation, and its deficiency disrupts normal neural tube closure
• Vitamin B12 deficiency: May also increase risk, particularly when combined with low folate status

Maternal health conditions

• Pre-gestational diabetes: Poorly controlled blood glucose levels during early pregnancy are linked to a higher risk of neural tube defects
• Maternal obesity: Excess maternal weight has been associated with increased rates of encephalocele and other birth defects, possibly due to metabolic, inflammatory, or hormonal factors

 Teratogenic exposures

• Certain medications: Such as valproic acid (used for epilepsy), carbamazepine, and isotretinoin, are known teratogens that may increase NTD risk
• Alcohol consumption, smoking, and recreational drug use: During pregnancy, these have been implicated in abnormal fetal development, including neural tube defects
• Exposure to environmental toxins: Pesticides, heavy metals, and industrial solvents may also elevate risk, though evidence is still emerging

Maternal infections

Infections such as rubella, cytomegalovirus (CMV), and toxoplasmosis during early pregnancy can interfere with fetal brain and skull development, potentially contributing to encephalocele formation.

Socioeconomic and geographic factors

Populations with limited access to prenatal care, poor maternal nutrition, and lack of folic acid supplementation programs may have a higher incidence of encephalocele. Seasonal variations in incidence have been noted in some studies, possibly linked to dietary changes and infection patterns.

Environmental risk factors are often preventable or modifiable, making them a key target for public health interventions. Maternal health optimization, folic acid supplementation, and avoidance of teratogens can significantly reduce the risk of neural tube defects, including encephalocele.⁴

Interaction between genetic and environmental factors

The development of encephalocele is rarely the result of a single cause; rather, it reflects a multifactorial etiology, where genetic susceptibility interacts with environmental triggers. This interaction is crucial for understanding why some pregnancies are affected despite similar exposures, while others remain unaffected.

Gene–environment interplay

Variants in genes involved in neural tube development, such as those regulating folate metabolism (e.g., MTHFR, MTRR), may increase vulnerability to folate deficiency. In such cases, inadequate maternal folic acid intake may amplify the effect of the genetic predisposition, leading to abnormal neural tube closure.

Epigenetic modifications

Environmental factors can alter gene expression through epigenetic mechanisms, including DNA methylation and histone modification. For example, maternal malnutrition, hyperglycemia, or toxin exposure during early gestation can disrupt normal epigenetic regulation, silencing or activating key developmental genes.

Threshold effect

Encephalocele is often considered a threshold trait in multifactorial inheritance models—meaning the combined genetic and environmental burden must cross a certain threshold for the defect to manifest. This explains why recurrence risk is higher in families with one affected child, as the genetic predisposition remains constant, but environmental optimization can lower risk.

Clinical and public health implications

Recognizing the combined effect of genes and environment underscores the importance of preconception counseling, targeted folate supplementation, and careful medication review for women planning pregnancy. Genetic testing may help identify at-risk families, allowing for closer monitoring and early prenatal screening.

Diagnostic approach

Early and accurate diagnosis of encephalocele is essential for guiding pregnancy management, surgical planning, and parental counseling. The diagnostic process combines prenatal imaging, postnatal assessment, and in some cases, genetic evaluation.

Prenatal diagnosis

• Ultrasound screening:
  
  • Second-trimester anomaly scan (18–20 weeks) is the most common method of detecting encephalocele
  • Appears as a cystic or solid mass protruding through a skull defect, often along the midline
  • Color Doppler can help differentiate encephalocele from other masses by demonstrating vascular structures
    
• First-trimester detection:
  
  • High-resolution transvaginal ultrasound may detect large defects earlier, particularly in high-risk pregnancies

Advanced Imaging

• Fetal MRI:
  
  • Provides superior visualization of brain structures, the extent of herniated tissue, and associated anomalies
  • Helps refine prognosis and surgical planning

Postnatal Evaluation

• Clinical examination:
  
  • Inspection of the skull defect, assessment of neurological function, and evaluation for other congenital anomalies.
    
• Neuroimaging:
  
  • CT scan or MRI confirms diagnosis, defines skull defect size, and detects complications such as hydrocephalus.

Genetic testing and counseling

• Chromosomal microarray or whole-exome sequencing:
  
  • Recommended when encephalocele is associated with other anomalies or suspected genetic syndromes
  • Identifies chromosomal abnormalities or gene mutations that can influence recurrence risk counseling

Multidisciplinary Assessment

Diagnosis should involve a team including obstetricians, radiologists, neonatologists, neurosurgeons, and genetic counselors to plan perinatal care, discuss prognosis with parents, and consider timing and approach for surgical repair.

Early and comprehensive diagnosis improves outcomes by allowing timely decision-making, preparation for delivery in a tertiary care center, and optimal management of associated complications.

Prevention Strategies

Preventing encephalocele relies on reducing modifiable risk factors and optimizing maternal health before and during pregnancy. Although not all cases can be prevented—especially those with a strong genetic component—several interventions have been shown to significantly lower the risk of neural tube defects.

Folic Acid Supplementation

• Preconception supplementation: Using supplements such as folic acid is the single most effective preventive measure against neural tube defects, including encephalocele
• Recommended dose:
  • 400 mcg/day for women of reproductive age
  • 4 mg/day for high-risk women (previous child with NTD, diabetes, or use of anticonvulsants)
• Supplementation should begin: At least one month before conception and continue through the first trimester

Maternal health optimisation

• Diabetes management: Achieving good glycemic control prior to conception reduces risk
• Weight management: Maintaining a healthy BMI lowers the likelihood of obesity-related pregnancy complications and congenital anomalies
• Management of chronic illnesses: Preconception counseling for conditions such as epilepsy (with review of teratogenic medications) helps minimize exposure risks

Avoidance of Teratogenic Agents

• Careful review of medications: Particularly antiepileptics and retinoids, with substitution of safer alternatives when possible
• Avoidance of alcohol, tobacco, and illicit drugs during pregnancy
• Limiting exposure to environmental toxins: Pesticides and heavy metals can have damaging effects

Public Health and Nutritional Interventions

• Food fortification programs: With minerals such as folic acid have proven effective in reducing neural tube defect incidence at the population level
• Education and awareness campaigns: Used to inform women of reproductive age about the importance of periconceptional folate intake

Genetic Counseling

• For families with a history of encephalocele or other neural tube defects: Preconception genetic counseling helps assess recurrence risk and plan for early prenatal screening.

By combining nutritional, medical, and public health approaches, the incidence of encephalocele can be significantly reduced, improving neonatal survival and long-term outcomes.

Summary

Encephalocele remains a rare but serious congenital neural tube defect with significant implications for neonatal health, development, and quality of life. Its occurrence is shaped by a complex interplay between genetic predisposition and environmental influences, such as maternal nutrition, health status, and teratogen exposure. Advances in prenatal imaging and genetic testing have improved early detection, enabling informed decision-making and multidisciplinary management.

Preventive strategies, particularly periconceptional folic acid supplementation and optimization of maternal health, play a vital role in reducing risk. Public health interventions, education, and genetic counseling further strengthen prevention efforts, particularly in high-risk populations.

Continued research into the molecular mechanisms of neural tube closure and gene–environment interactions will pave the way for better prediction, prevention, and targeted therapies. Ultimately, a comprehensive approach—spanning genetic insight, environmental risk reduction, and early clinical intervention—offers the best opportunity to improve outcomes for infants affected by encephalocele and support families in managing this challenging diagnosis.⁵