Occipital encephalocele

Findings

There is a large occipital encephalocele, containing mixed solid and cystic areas. The calvarial defect is between 1-2 cm, through which brain tissue is seen to herniate

Differential diagnosis:
- Occipital encephalocele
- Cystic hygroma
- Teratoma
- Branchial cleft cyst
- Scalp edema
- Epidermal scalp cyst


Diagnosis: Occipital encephalocele


Key points

An encephalocele results from failure of the surface ectoderm to separate from the neuroectoderm. The final result is a bony defect in the skull table, which allows herniation of the meninges (cranial meningocele) or herniation of brain tissue.
Encephaloceles represent 10-15% of all neural tube defects.
Of encephaloceles, occipital encephaloceles are most common (75-80%). 90% are midline.
The absence of brain tissue within the herniated sac is the single most favorable prognostic feature for survival.
Incidence ranges from 1 in 3000 (Southeast Asia) to 1 in 10,000 live births (North America).
Once an encephalocele is diagnosed, a search for associated intracranial and extracranial abnormalities (60-80%) should be performed. 15-20% have additional severe CNS defects including additional neural tube defects, Dandy-Walker malformation, Chiari malformation, hydrocephalus and optic nerve malformations.
The risk of chromosomal abnormalities is 13-44%; therefore, karyotyping should be offered to the mother. Most common chromosomal anomaly is Trisomy 18.
Associated with genetic syndromes such as Meckel-Gruber, von Voss, Chemke, Roberts, and Knobloch syndromes. Important to evaluate digits for polydactyly, kidneys, and for oligohydramnios to exclude Meckel-Gruber syndrome.
Diagnosis is thought to be impossible before skull ossification starts at 10 weeks gestation. Earliest U/S diagnosis has been at 13 weeks.