37 Congenital Encephaloceles

• Encephaloceles refers to a herniation of brain tissue, which protrudes through a defect in the skull base and maintains a connection to the subarachnoid space.1

• They can broadly be classified as either primary or secondary:

Primary encephaloceles (Table 37.1) are congenital and are present at birth. They are a type of neural tube defect and can occur in isolation or with other syndromes, resulting from the failure of separation from the surface ectoderm and the neuroectoderm.

Secondary encephaloceles are more common and can be a result of trauma (accidental or iatrogenic), infection, tumor related, or possibly secondary to elevated intracranial pressures (i.e., spontaneous).³ Frequently associated with cerebrospinal fluid (CSF) fistula (see Chapter 32).

• By definition, cephalocele refers to the sac-like protrusion of cranial contents through a defect in the skull base/cranium.

An encephalocele contains brain tissue alone.

A meningoencephalocele contains brain tissue and meninges.

A meningocele contains only meninges.

Epidemiology

• Incidence: 0.8 to 5 per 10,000 live births.^4,5 Males and females are equally affected. Occipital encephaloceles are most frequent in North America and Western Europe,⁶ and sincipital and basal encephaloceles are more frequent in Southeast Asia, Russia, and central Africa (incidence of 1 in 3,500 to 1 in 5,000 live births).7

Table 37.1 Classification of Primary Encephaloceles Based on Location and Anatomic Defect

Occipital Encephaloceles2,8

• Present at birth.

• May be diagnosed prenatally by ultrasound.

• Neural tissue is covered with skin.

• Neural tissue can involve nonfunctioning gliotic tissue, cerebral tissue, or cerebellar tissue.

• Can have cranial nerve defects, developmental delay, blindness, seizures.

• Neurologic symptoms often related to degree of cerebral or cerebellar dysplasia.

• May be progressive if hydrocephalus develops after birth.

• May be associated with Chiari malformations or other syndromes (e.g., Meckel-Gruber syndrome).⁹

Sincipital Encephaloceles¹⁰

• Are typically visible on the face.

• Can range from small occult lesions to large pulsatile masses with significant facial deformity.

• They can be classified according to the exit point on the face11: interfrontal, nasofrontal, nasoethmoidal, naso-orbital.

• Unlike dermoids and gliomas, sincipital encephaloceles on the face are pulsatile because of their connection to the subarachnoid space.

Basal Encephaloceles^2,10

• Because of their location at the base of the skull, basal encephaloceles may not have any external manifestations.

• Some patients may have a concurrent broad nasal bridge or other midfacial anomalies.

• Frequently presents as nasal obstruction, CSF rhinorrhea, or recurrent meningitis. They may not become apparent until later in life.

• Have been classified based on their anatomic location along the skull base¹²: transethmoidal, sphenoethmoidal, spheno-orbital, sphenomaxillary, transsphenoidal.

Temporal Lobe Encephaloceles

• Can be further classified based on location¹³ (Table 37.2):

Congenital temporal encephaloceles are present at birth but may not have significant clinical symptoms until adulthood.¹⁴

Diagnosis is challenging, as symptoms may be nonspecific and can include otorrhea, recurrent ear infections, conductive hearing loss, and recurrent meningitis.¹⁵

Occasionally, the associated CSF leak may present as clear rhinorrhea, as the CSF flows into the nasal cavity via the eustachian tube.

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Hi-Tech Tools in Skull Base Surgery Pediatric Skull Base Skull Base Imaging Skull Base Infections Skull Base Reconstruction Techniques Transcranial Approaches to the Skull Base

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