Cephalocele

Cephalocele refers to the outward herniation of CNS contents through a defect in the cranium. The vast majority are midline.

Epidemiology

The estimated incidence is 0.8-4:10,000 live births ¹³ with a well recognized geographical variation between types; however, this has been speculated to be underestimated as many may result in elective termination, in utero demise, or stillbirth. There may be a female predilection ¹¹.

Clinical presentation

The presentation may vary widely depending upon the type of defect.

Examples include:

• large mass seen extending from cranium on prenatal ultrasound
• small cranial soft tissue mass palpated in childhood (e.g. atretic cephalocele)
• in utero demise (severe defect)

Pathology

It is thought to arise due to failed closure of the rostral end of the neuropore. This may result from either overgrowth of neural tissue in the line of closure, or failure of induction by adjacent mesodermal tissues which interferes with normal skull closure.

Classification

Cephaloceles can be classified into 5 types, based upon the herniated contents ¹⁵:

• meningocele: CSF lined by meninges
• gliocele: CSF lined by glial tissue
• meningoencephalocele: CSF, brain, and meninges
• meningoencephalocystocele: CSF, brain, meninges, and part of a ventricle and choroid plexus
• atretic cephalocele: dura, fibrous tissue, and degenerated brain

Location

• occipital cephalocele: most common, up to 75%
• parietal cephalocele: up to 37% ¹²
• frontal cephalocele/fronto-ethmoidal cephalocele: ~10%, this type is most common in Asia
• petrous apex cephalocele ⁵: rare
• intra sphenoidal cephalocele ¹⁰: rare 

Associations

Additional congenital anomalies may be present in up to 50 % of cases. They include

• aneuploidic
  • trisomy 13
  • trisomy 18 ⁶
• non-aneuploidic syndromic
  • Meckel-Gruber syndrome: occipital ⁶
  • Walker-Warburg syndrome
  • fronto-nasal dysplasia
• non-syndromic CNS anomalies
  • fetal hydrocephalus/neonatal hydrocephalus
  • microcephaly: ~20% of cases ^ref
  • Dandy-Walker continuum
  • dysgenesis of corpus callosum
  • spina bifida
• non-syndromic non-CNS anomalies
  • cleft lip and palate
  • congenital cardiovascular anomalies
  • hypertelorism
  • amniotic band syndrome ⁶: if there is an unlucky slash defect around the occipital region

Markers

• maternal serum alpha-fetoprotein (MSAFP) may be elevated

Radiographic features

Ultrasound

Sonographically, these lesions may appear as:

• a cyst protruding from the fetal calvarium representing a meningocele or cyst within cyst appearance
• a solid mass protruding from the calvarium representing a herniated brain: encephalocele 
• either or both of the above associated with a defect in the calvarium

Treatment and prognosis

The overall prognosis is variable dependent on severity and other associations (presence of hydrocephalus, microcephaly, etc). If a large cephalocele is noted in an antenatal ultrasound scan, it generally implies a poor prognosis.