Skull base surgery is a surgical procedure that treats lesions at the skull base. It is used for tumours, congenital defects at the skull, cerebrospinal (CSF) fluid leaks and blood vessel lesions while protecting critical neurovascular structures. This multidisciplinary surgery integrates both neurosurgery and otorhinolaryngology, employing two major approaches: open transcranial and endoscopic endonasal approach (EEA). EEA is often preferred, yet open transcranial techniques are still being employed to treat complex or laterally extended lesions. This field has evolved from early open procedures in the late 19th century to modern endoscopic techniques, leading to widened indications and improvements in surgical outcomes. The field continues to focus on the advancement of surgical visualisation and reconstruction techniques, complication management, and addressing global challenges in its accessibility.
Uses Skull base surgery focuses on treating lesions (damaged tissues) in the intricate anatomical region of the skull base. Surgeons select between the minimally invasive endoscopic endonasal approach (EEA) and the traditional open transcranial approach.
Neoplastic lesions (tumours) A major indication for skull base surgery is tumours. They can be classified by their benign (non-cancerous) or malignant (cancerous) nature and their anatomical location (at the anterior, middle, or posterior cranial fossa). For craniopharyngiomas, the tumour is removed to achieve a higher gross total resection (GTR) rate, improvements in visuals, lower recurrence and lower permanent diabetes insipidus rates when EEA is used compared with the transcranial approach. For chordomas, both approaches have similar survival outcomes after tumour removal, but EEA reduces worsening cranial nerve function better. For pituitary adenomas, both approaches have similar GTR rates, with EEA associated with better recovery of vision. EEA is generally favoured for tumours due to its advantages. However, surgeons still need to retain open approaches in their toolkit as it is reserved for skull base tumours that have invaded structures like orbit and intradural compartments (i.e. sphenoorbital meningioma) or further disease developments that result in the inability of a second endoscopic approach. Other cases of favouring an open approach over EEA include considerations like the tumour extending over the orbital roof or prioritising olfaction (smelling) preservation.
Congenital lesions Congenital (present from birth) skull base lesions (e.g. encephaloceles, fibrous dysplasia or other developmental defects) are rarer indications. Intervention is required when they cause complications such as mass effect (a growing mass that pushes its surrounding tissue), cerebrospinal fluid leakage or recurrent infections leading to meningitis or forming brain abscess. For anterior congenital cephaloceles (a subtype of encephaloces), EEA removes the protruding tissue with lower complications and mortality post-operation than open surgery.
Cerebrospinal fluid (CSF) leaks CSF leaks are classified as traumatic (resulting from accidental or iatrogenic injury: healer-caused harm) or non-traumatic (birth defects, infections, inflammation). For CSF rhinorrhea (CSF leakage into the nose), EEA seals the leak site and is established as the gold-standard treatment, with meta-analyses reporting the pooled primary repair success rate and overall success after surgery redo being 93.7% and 99.7% respectively.
Vascular abnormalities In rare selected cases, EEA provides access to treat vascular abnormalities such as paraclinoid aneurysms (bulges in the wall of the internal carotid artery) or cavernous malformation that lie next to the brainstem. However, EEA currently plays a limited role and is continuously evolving, although it may already offer improvements in visualisation and vascular control.
Contraindications Absolute contraindications of endoscopic endonasal surgery (EEA), where the approach should never be used, include the presence of active bacterial sinusitis, as no surgery should be performed until the infection is cleared. If the tumour has extended laterally beyond boundaries set by critical neurovascular structures, EEA should not be used as the only approach, as a microscopic, open transcranial or combined approach may be required instead. Other absolute contraindications include total maxillectomy (removal of upper jawbone), orbital exenteration (removal of eye socket), resection of fascial skin or anterior wall of frontal sinus and aggressive tumour wrapping around the internal carotid artery. Relative contraindications to EEA, which make the procedure risky but not completely forbidden, include medical comorbidities (co-occurrence of chronic diseases), such as severe sleep apnea or granulomatosis with polyangiitis. Others include decreased sinus pneumatization (presence of air spaces between bones), narrow piriform aperture(significant for patients less than 2 years old). Furthermore, the surgeon's insufficient experience, as this surgery requires extensive familiarity with vital neurovascular structures, and lack of advanced hospital equipment, are considered relative contraindications.
Preference for non-surgical alternatives Stereotactic radiosurgery can be applied to benign tumours such as meningioma that are asymptomatic or mildly symptomatic, and is even used as a standard treatment for those that are especially small or incidentally discovered. This alternative is suitable for elderly patients with serious comorbidities and poor health status, with the consequences of surgical risks outweighing tumour control.
Risk and complications
Cerebrospinal fluid leak and meningitis Cerebrospinal fluid (CSF) leak is the most common risk of skull base surgery. The incidence rate is around 2.5-3%. The risk is significantly higher when tumours develop in the functional areas of the brain. CSF leakage can cause severe morbidity, including meningitis. Treatment includes a lumbar drain, ventriculoperitoneal shunt (a medical device to drain CSF) and surgical repair. It was found that the introduction of injectable hydroxyapatite and nasoseptal flap (a patient's own tissue from the nose) during the surgery would be an effective way to minimise CSF leakage, when compared with using nasoseptal flap alone.
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