What is a cephalocele?

What is a Cephalocele?

A cephalocele is a congenital malformation characterized by herniation of intracranial contents (meninges with or without brain tissue) through a focal defect in the skull. 1, 2

Pathophysiology and Classification

Cephaloceles are thought to arise after neurulation from a defect in the calvarial mesenchyme rather than as a classic neural tube defect. 1 They represent focal herniation of cranial contents through skull defects and can be classified based on:

By Contents:

• Meningocele: Contains only meninges and cerebrospinal fluid, without neural tissue 2, 3
• Encephalocele (or meningoencephalocele): Contains brain tissue in addition to meninges 1, 2
• Encephalocystocele: Contains central nervous system tissue with the ventricular system 4

By Anatomical Location:

• Calvarial encephaloceles: Can arise anywhere along the midline skull from the orbits to the craniocervical junction 1
• Occipital: Most common in European and North American populations 1, 3
• Frontal/sincipital (fronto-ethmoidal): Most common among Asian populations 1, 2
• Parietal, ethmoidal, sphenoidal: Less common variants 3, 5

Special Variant: Atretic Cephalocele

Atretic parieto-occipital encephaloceles deserve special mention because they can be confused with cutis aplasia congenita. 1 These present as:

• A small area of dysplastic skin overlying the parietal or occipital bones 1
• Surrounded by whorls of distinctly colored hair, sometimes called a "horse collar" 1
• May show an underlying small bony defect and/or bifid superior sagittal sinus on neuroimaging 1
• MRI with magnetic resonance venography reveals a characteristic venous drainage pattern where the straight sinus is atretic or absent and deep cerebral veins drain through an embryonic primitive prosencephalic (falcine) vein 1, 6

Clinical Significance and Prognosis

The outcome for encephaloceles is variable and depends largely on the amount and type of neural tissue within the sac. 1 Specifically:

• Large occipital encephaloceles containing solely or largely CSF may have an excellent prognosis 1
• Those containing large amounts of occipital lobe or brainstem generally have a poor prognosis 1
• Occipital cephaloceles are frequently associated with hydrocephalus (found in approximately 59% of cases based on surgical series) 3

Associated Conditions

Cephaloceles may be:

• Isolated malformations 1
• Associated with a wide variety of genetic syndromes and malformation sequences 1
• Accompanied by other brain malformations including hydrocephalus, corpus callosum hypoplasia, and cerebellar abnormalities 4

Diagnostic Approach

MRI is the preferred imaging modality and provides superior visualization of both the extent and type of neural tissue within the sac. 1 The diagnostic workup should include:

• MRI with magnetic resonance venography to identify associated brain malformations and characteristic venous drainage patterns 6
• CT scan may play a supplementary role in identifying bony defects and intracranial calcifications 1
• Three-dimensional CT scan of the facial skeleton for sincipital encephaloceles 2

Critical Pitfalls

A midline cutis aplasia congenita that exposes the superior sagittal sinus can be dangerous for two reasons: 1

1. It can serve as a portal of entry for bacterial meningitis or intracranial infection 1, 6
2. If allowed to desiccate from exposure to air, the dura lining the superior sagittal sinus can crack and bleed significantly 1

Such lesions should be immediately covered with sterile, saline-soaked gauze or petroleum gel. 1