Encephalocele

An encephalocele is a protrusion of brain tissue and meninges through a defect in the skull. Congenital encephaloceles result from incomplete closure of the neural tube and are classified by location: occipital (the commonest type in Western populations), parietal, frontoethmoidal (sincipital; common in Southeast Asia) and basal (transethmoidal, sphenoethmoidal, transsphenoidal, spheno-orbital). Acquired encephaloceles follow trauma or surgery, or arise spontaneously at thin areas of the skull base.

Spontaneous adult skull-base encephaloceles are strongly associated with raised intracranial pressure, typically in obese middle-aged women with features of idiopathic intracranial hypertension. Common sites are the lateral recess of the sphenoid sinus, the cribriform plate and the tegmen of the temporal bone^[1].

Congenital lesions present as a visible mass at birth, with associated brain malformations, hydrocephalus and developmental delay. Basal encephaloceles may present as a nasal mass, nasal obstruction, hypertelorism or CSF rhinorrhoea. Adult spontaneous lesions present with clear rhinorrhoea or otorrhoea (often mistaken for rhinitis or serous otitis media), recurrent bacterial meningitis, or conductive hearing loss in temporal-bone lesions. Seizures can occur when temporal-lobe tissue herniates.

Thin-section CT localises the bony defect; MRI (especially T2-weighted imaging) shows the contents of the sac and distinguishes brain from fluid, mucosa or tumour. Beta-2 transferrin testing of fluid confirms CSF. MRI signs of raised pressure (empty sella, flattened posterior globes, transverse sinus stenosis) and multiple bony defects suggest IIH, and lumbar opening pressure may be measured. A nasal mass in a child must not be biopsied until an encephalocele has been excluded.

The principles are reduction or amputation of the non-functional herniated tissue, closure of the dural defect, and multilayer reconstruction of the skull base. Anterior and sphenoid encephaloceles are now mostly repaired endoscopically through the nose, using free grafts or vascularised flaps such as the nasoseptal flap^[2]. Lateral recess sphenoid defects may require a transpterygoid approach. Tegmen defects are repaired through a middle-fossa craniotomy, a transmastoid approach, or both^[1,3].

Untreated raised intracranial pressure is the main cause of failure and of new leaks at other sites, so pressure is assessed and treated (weight loss, acetazolamide, or CSF diversion) as part of the plan^[1].

Primary endoscopic repair succeeds in most patients. Risks include recurrent leak, meningitis, intracranial haemorrhage from the herniated tissue, and, in congenital lesions, worsening hydrocephalus after closure. In children, outcome depends mostly on the associated brain malformations and the amount of brain within the sac.