What Is Encephalocele?
Brain encephalocele is a rare congenital cranial malformation in which a developmental fusion defect of the fetal skull bones allows brain tissue and/or its protective membranes to protrude outward through a bone defect. It is classified under neural tube defects (NTDs) and represents one of the severe forms of congenital central nervous system anomalies.
Neural tube closure normally occurs around the 3rd to 4th week of embryonic development. When this critical fusion process fails, an opening remains within the cranial bones, creating a pathway for herniation and leading to the formation of an encephalocele.
The content of the herniated sac varies; therefore, encephaloceles are divided into subtypes:
Types of Encephalocele
Meningocele: A sac containing only cerebrospinal fluid and meninges protrudes externally. No brain tissue is present within the sac.
Meningoencephalocele: Both meninges and brain tissue form the herniated sac. This is the most common encephalocele subtype.
Encephalomyelocele: A more severe form where both brain and spinal cord tissues herniate through the cranial defect.
Most cases present at birth with a visible, sac-like mass on the head and are frequently associated with additional structural anomalies.
Embryology and Pathophysiology
Failure of neural tube closure during early embryogenesis disrupts cranial bone formation and fusion. The resulting skull defect allows cerebrospinal fluid pressure to push neural tissues outward, forming a herniated sac.
The sac may contain:
Cerebrospinal fluid
Meninges
Brain parenchyma
In rare cases, vascular structures
The severity of clinical outcomes correlates strongly with the sac contents and associated intracranial abnormalities.
Anatomical Locations
Encephaloceles may occur in several cranial regions, including:
Occipital region
Frontonasal region
Parietal region
Bregmatic area
Rarely, Sphenoidal region
Etiology and Risk Factors
There is no single definitive cause of encephalocele. A multifactorial etiology involving genetic, environmental, and maternal metabolic factors is recognized.
Genetic and Chromosomal Associations
Encephalocele may occur with certain genetic syndromes and chromosomal anomalies, such as:
Trisomy 13 (Patau syndrome)
Trisomy 18 (Edwards syndrome)
Walker–Warburg syndrome
Knobloch syndrome
Roberts syndrome
Frontonasal dysplasia
Dissegmental dysplasia
Pseudo-Meckel syndrome
These conditions commonly feature craniofacial malformations and increased susceptibility to neural tube defects.
Environmental and Maternal Factors
Documented maternal risk contributors include:
Folate deficiency
Maternal diabetes
Teratogenic medication exposure (e.g., antiepileptics)
Alcohol and tobacco consumption
Radiation exposure
Amniotic band sequence
Maternal obesity
Among these, insufficient folic acid intake before conception and in early pregnancy is one of the strongest modifiable risk factors.
Clinical Features and Symptoms
The clinical presentation of encephalocele varies according to lesion size, sac contents, and associated brain malformations.
Local Signs
Externally visible cranial mass
Thinned or stretched overlying skin
Possible cerebrospinal fluid leakage
Craniofacial deformities
Neurological Manifestations
Intellectual disability
Global developmental delay
Motor dysfunction
Visual or auditory impairment
Hydrocephalus
Seizures
Brainstem-related symptoms
Symptom severity parallels the complexity of the herniated structures: Small meningoceles may produce minimal neurologic deficit, while large meningoencephaloceles are often associated with significant neurodevelopmental impairment.
Prenatal Diagnosis
Today, encephalocele can usually be detected during routine prenatal screening.
Ultrasonography
Identifies cranial bone defects
Demonstrates sac morphology and contents
Commonly visualized during second-trimester examinations
Fetal MRI
Superior in differentiating lesion contents
Guides postnatal surgical planning
It is also essential to evaluate for coexisting anomalies such as:
Hydrocephalus
Chiari malformation
Corpus callosum defects
Spinal abnormalities
Early diagnosis helps in parental counseling, pregnancy decision-making, and preparation for postnatal management.
Treatment Approach
Surgical Management
Surgery is the primary treatment for encephalocele. Goals of the operation include:
Removal of the herniated sac
Preservation of viable brain tissue
Secure closure of cerebrospinal fluid pathways
Reconstruction of cranial defects
Surgery is typically scheduled during early infancy, depending on lesion complexity and the baby’s clinical condition.
Postoperative and Long-Term Care
Hydrocephalus may develop, requiring ventriculoperitoneal shunting.
Long-term neurological rehabilitation is often needed.
Ongoing developmental screening and supportive treatment improve outcomes.