Prenatal Diagnosis of Encephalocele
What is an Encephalocele?
Herniation of intracranial contents through a bony calvarial defect — a severe form of neural tube defect occurring during primary neurulation.
Meningocele
Sac contains CSF only. No brain parenchyma. Relatively favorable prognosis.
Meningoencephalocele
Sac contains CSF + brain tissue ± ventricles. Significantly worse outcomes.
The distinction between these two subtypes is the single most important prognostic determinant in prenatal counseling.
Incidence & Geographic Distribution
U.S. prevalence: approximately 1 in 9,100 live births (CDC, 2018-2022). Frequency and phenotype vary by population.
| Region | Predominant Location | Notes |
|---|---|---|
| Western Hemisphere | Occipital (80–90%) | Female predominance (~70%) |
| Southeast Asia | Anterior / Sincipital | Frontoethmoidal subtype |
A closed, skin-covered defect may not produce a clearly elevated maternal serum AFP. Detailed ultrasound remains central to diagnosis.
Ultrasound: Primary Screening
Detection is possible in the first trimester. Targeted neurosonography defines the skull defect, sac contents, and associated findings.
- ▶ Paracranial cystic or heterogeneous mass in direct continuity with intracranial space
- ▶ Visualized bony calvarial defect — the hallmark finding
- ▶ Microcephaly: head circumference <3rd percentile suggests significant brain herniation
- ▶ MSAFP often normal in closed defects — do not rely on biochemistry alone
3D ultrasound enhances delineation of the calvarial defect and sac morphology.
Fetal MRI: Characterizing What Matters
After ultrasound suspicion or diagnosis, fetal MRI can refine counseling and neonatal planning by clarifying intracranial anatomy and sac contents.
- ✓ Distinguishes meningocele (CSF) from meningoencephalocele (brain tissue)
- ✓ Maps dural venous sinuses — sagittal & transverse — critical for surgical safety
- ✓ Identifies associated CNS anomalies: Chiari, Dandy-Walker, ACC, ventriculomegaly
- ✓ Assesses remaining supratentorial brain volume
- ▶ Venous sinus involvement = high surgical risk for catastrophic hemorrhage
Cystic Hygroma vs. Occipital Encephalocele
Cystic Hygroma
Septated, posterior neck. Intact skull. No intracranial connection. Strongly associated with chromosomal aneuploidies (Turner syndrome, T21, T18).
Occipital Encephalocele
Posterior skull defect present. Direct intracranial communication. May contain brain parenchyma. Requires neurosurgical planning.
Key imaging question: Is the cranial vault intact? Doppler may help identify venous flow within the sac in encephalocele.
Sincipital (Frontoethmoidal) Encephalocele
Anterior defects (nasofrontal, nasoethmoidal, nasoorbital) are more common in Southeast Asia and carry unique clinical challenges.
- ▶ Facial deformity and airway compromise at birth
- ▶ High association with hypothalamic-pituitary dysfunction
- ▶ Screen for: central adrenal insufficiency, growth hormone deficiency, diabetes insipidus
- ✓ Generally better cognitive outcomes than occipital lesions
- ✓ Complex craniofacial reconstruction often achieves good cosmetic results
Endocrine evaluation is mandatory in the neonatal period for all anterior encephaloceles.
Syndromic Associations
Encephalocele may be isolated or a component of a major genetic syndrome. The distinction dramatically changes recurrence risk counseling.
Meckel-Gruber Syndrome
Autosomal recessive. Triad: occipital encephalocele + postaxial polydactyly + bilateral multicystic dysplastic kidneys. Lethal. Recurrence risk: 25%.
Chromosomal Aneuploidies
Trisomy 13 and Trisomy 18 are strongly associated. Amniotic band syndrome produces asymmetric, non-midline defects.
Offer diagnostic testing with chromosomal microarray when a structural anomaly is identified. Consider sequencing with genetics guidance when additional anomalies or a syndromic pattern are present.
Pregnancy Surveillance & Delivery Planning
Multidisciplinary Consultation
MFM + Pediatric Neurosurgery + Neuroradiology + Neonatology + Genetics + Palliative Care
Serial Surveillance
Individualize follow-up to monitor ventricles, growth, amniotic fluid, lesion evolution, and family goals
Genetic Testing
Offer diagnostic testing with microarray; consider sequencing when phenotype suggests a monogenic syndrome
Delivery Planning
Individualize timing and route according to lesion size and contents, rupture risk, hydrocephalus, obstetric factors, planned neonatal care, and goals of care.
Postnatal Care & Surgical Repair
Immediate Stabilization
Sterile warm saline-moistened non-adherent dressings. Prevent desiccation, rupture, and CSF leak. Careful airway management.
Surgical Repair
Timing depends on skin coverage, CSF leak or rupture, airway concerns, associated anomalies, and neonatal/neurosurgical assessment.
Hydrocephalus Surveillance
Assess for evolving hydrocephalus; some neonates require CSF diversion after repair.
Endocrine Screening (Anterior Lesions)
Screen for central adrenal insufficiency, GH deficiency, and diabetes insipidus. Prevent adrenal crisis.
The Giant Encephalocele Paradox
A dramatic external sac does not by itself define neurologic prognosis. Modern imaging clarifies the structures involved.
Giant Sac — Mostly CSF
A large sac with limited neural tissue may be more surgically approachable than its size suggests.
Small Sac — Eloquent Tissue
A smaller lesion involving critical neural tissue may carry substantial neurologic risk.
Contents, remaining brain, venous anatomy, hydrocephalus, and associated anomalies matter more than size alone.
