Cephalocele

Cephalocoele 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 recognised geographical variation between sub types. Thee may be a greater female predilection ¹¹.

Pathology

It is thought to arise due to failure of closure of the rostral end of the neuropore resulting from either overgrowth of neural tissue in the line of closure or a failure of induction by adjacent mesodermal tissues which in turn interfere with normal closure of the skull.

Sub types

There are two main subtypes:

• encephalocoele: herniation of meninges and CSF and brain parenchyma
• cranial meningocoele: herniation of meninges and CSF only

Classification

Cephalocoeles can also be subclassified into 5 subtypes ¹⁵:

• meningocele: contains CSF and lined by meninges
• gliocele: contains CSF and lined by glial tissue
• meningoencephalocele: contains CSF and brain
• meningoencephalocystocele: CSF, brain and ventricles
• atretic cephalocele: small nodule of fibrous-fatty tissue

Location

• occipital cephalocoele: most common, up to 75%
• parietal cephalocoele: up to 37% ¹² 
• frontal cephalocoele/fronto-ethmoidal cephalocoele: ~10%, this type is most common in Asia
• petrous apex cephalocoele ⁵: rare
• intra sphenoidal cephalocoele¹⁰: 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: ~ 20~20% of cases ^ref
  • Dandy-Walker continuum
  • dysgenesis of corpus callosum
  • spina bifida 
• non-syndromic non CNS-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 feto proteinfetoprotein (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 -: encephalocoele 
• 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 cephalocoele is noted in an antenatal ultrasound scan it generally implicates a poor prognosis.