- Congenital bony defect in skull base
- Traditionally classified with neural tube defects (NTD), but embryogenesis can occur after closure of neural tube.
- Most cases sporadic
- Exact cause unknown
- Can be isolated or associated with other malformations.
- Agenesis of corpus callosum, Dandy-Walker malformation, hydrocephalus, holoprosencephaly (Bersani, OPRS 2006)
- Traumatic skull base or orbital roof fracture
- Relatively small (2–4 mm) roof fractures can cause delayed encephaloceles in children (Cayli, Pediatr Neurosurg 2003).
- Orbital or skull base surgery
- Tumor resection
- LeFort III osteotomy (Ridgway, J Craniofac Surg 2011)
- Medial orbital decompression (Murchison, OPRS 2012)
- Malignant or inflammatory conditions of bone, meninges, or sinuses (e.g., eosinophilic granuloma, natural killer T-cell lymphoma, cocaine abuse)
- Gorham-Stout syndrome ("disappearing bone disease") (Krohel, AJO 2002)
- Rare idiopathic osteolytic condition, often affects skull and face
- Worldwide incidence of encephalocele (all types) 1 in 5000 births; lower in North America: 1 in 10,000–15,000 (Sever, Teratology 1982)
- Posterior (occipital) location predominates in North America, Europe, Australia, Japan (Hunt, Plast Reconstr Surg 2003).
- Anterior more common in Southeast Asia and Russia
- No familial pattern
- Traumatic: Typically children or young male adults
- Congenital cases usually apparent at or shortly after birth
- Associated with numerous craniofacial anomalies and clefting syndromes
- Undiagnosed cases can sometimes present with meningitis, CSF leak, seizures, or nasal airway obstruction.
- Acquired: history of craniofacial trauma, orbital or skull base surgery
Herniation of intracranial tissue into orbit:
- Meningocele: meninges
- Encephalocele: brain tissue (often disorganized or infarcted)
- Meningoencephalocele: meninges and brain tissue
- Frontoethmoidal: majority of cases involving orbit
- Neurofibromatosis type 1 (NF1): sphenoid greater wing
- Fracture or surgery: orbital roof and/or medial wall
Orbital mass effect causes proptosis and/or downward/medial displacement of globe:
- Straining and crying might result in increased size of mass
- Pulsation of globe or mass
- Vision loss might result from strabismus or amblyopia (meridional or occlusional)
Herniated tissue can cause subcutaneous bulging or even peduculated mass in nasal or medial canthal region (Figure 1):
- Location typically above medial canthal tendon
Figure 1. Congenital bilateral frontoethmoidal meningoencephalocele.
- Elongation of face
- Nasal airway obstruction
- Dental malocclusion
Associated intracranial abnormalities:
- Cerebral dysplasia
- Agenesis of corpus callosum
Sometimes associated with other ocular anomalies:
- Morning glory syndrome
- Corneal clouding
- Nasolacrimal duct obstruction
- CT scan is best modality to demonstrate bony defect.
- 3D reconstruction can be helpful for operative planning (Figure 2).
- MRI provides excellent soft-tissue resolution.
Figure 2. Neuroimaging of patient in figure 1. A. 3-dimensional orbital CT reconstruction showing bilateral orbital roof and medial wall defects with herniated cranial tissue (yellow). B. Same study with coronal cut showing communication of brain with orbit. C. Orbital MRI, coronal view.