Endoscopic endonasal skull base approaches: an overview

Key points

The expanded endonasal approach (EEA) divides the skull base into modules extending in the sagittal plane from the cribriform plate to the foramen magnum and in the coronal plane to the petrous apex, cavernous sinus and infratemporal fossa (Kassam et al., 2005).
The approach is best suited to midline lesions in which neurovascular structures are displaced laterally; lateral extension and vascular encasement are the main limits.
The vascularised nasoseptal flap (Hadad–Bassagasteguy flap) has markedly reduced the rate of postoperative CSF leak in large dural defects.
The most common complication is CSF leak; meningitis, internal carotid artery (ICA) injury, olfactory loss and sinonasal morbidity are other important risks.
This surgery requires a team model in which ENT and neurosurgery work together, and a stepwise training process.

Modular classification

Sagittal plane

Transcribriform: the anterior skull base from the crista galli to the planum sphenoidale; used for olfactory groove meningiomas, intracranial extension of sinonasal malignancies and encephaloceles.
Transplanum/transtuberculum: access to the suprasellar region; for lesions such as craniopharyngioma and tuberculum sellae meningiomas.
Transsellar: the standard endonasal approach for pituitary adenomas and the foundation of extended approaches.
Transclival: access to the upper, middle and lower thirds of the clivus; for tumours such as chordoma and chondrosarcoma.
Transodontoid: access to the craniocervical junction; described, together with the transclival module, in the second part of Kassam et al., which covers the region from the posterior clinoids to the foramen magnum.

Coronal plane

Coronal plane modules are based mainly on transpterygoid access through the pterygopalatine fossa and cover the region around the petrous ICA, the middle third of the clivus, the petrous bone, cavernous sinus, middle cranial fossa and the medial infratemporal fossa. Kassam et al. defined zones in this region above and below the petrous ICA and emphasised that the approach is feasible when the lesion is centrally located and neurovascular structures are displaced laterally.

Main indications

Pituitary adenomas and other sellar lesions (the most common pathology in the first 800-patient series of Kassam et al.).
Craniopharyngioma and selected midline meningiomas (olfactory groove, planum, tuberculum sellae); lateral extension and vascular relationships determine selection.
Clival and petroclival tumours such as chordoma and chondrosarcoma.
Sinonasal malignancies including olfactory neuroblastoma; alone or in a combined approach, provided oncological principles (negative surgical margins) can be maintained.
CSF leaks and encephaloceles; repair in spontaneous, traumatic or iatrogenic cases.
Juvenile nasopharyngeal angiofibroma (JNA); usually considered together with preoperative embolisation.

Reconstruction

Skull base reconstruction is usually multilayered: inlay and/or onlay grafts (such as fascia lata or collagen matrix), fat and a vascularised flap on top. The septal mucoperiosteal–mucoperichondrial flap pedicled on the nasoseptal artery, described by Hadad et al. in 2006 (Hadad–Bassagasteguy flap), can be used for anterior, middle, clival and parasellar defects. In the first 43-patient series, postoperative CSF leak was reported at 5%.

In the Pittsburgh group's 800-patient series, the overall postoperative CSF leak rate was 15.9% and fell below 6% with the use of vascularised tissue. When the flap is likely to be needed, it is usually raised at the start of surgery. In a randomised trial of intradural surgery with high-flow leak risk, short-term lumbar drainage together with the nasoseptal flap reduced CSF leak (8.2% vs 21.2%).

Limits and complications

Limits

Tumours extending well lateral to the ICA or optic nerve may not be safely removable through the endonasal corridor; transcranial or combined approaches are then considered.
Encasement of major vessels, firm tumour consistency and previous radiotherapy make dissection harder and may change the resection goal.
If the septum or sphenopalatine vessels were affected by previous surgery, the nasoseptal flap may not be available; alternative flaps should be planned.

Complications

CSF leak and related meningitis; intracranial infection was reported at 1.6% in the 800-patient series.
ICA injury is rare but life-threatening; navigation, Doppler and a prepared haemorrhage management plan are important.
Temporary or permanent neurological deficit, cranial nerve injury and pituitary dysfunction (including diabetes insipidus).
Olfactory loss and sinonasal morbidity: crusting at the flap donor site continues until mucosalisation is complete (usually 6–12 weeks); saline irrigation and endoscopic debridement may be needed during this period.

Teamwork and the learning curve

Endonasal skull base surgery relies on a "two surgeons, four hands" model in which ENT and neurosurgery work together in the same operation; multidisciplinary assessment with endocrinology, ophthalmology, neuroradiology, interventional radiology, radiation oncology and pathology is required. Snyderman et al. described a stepwise training programme based on technical difficulty, neurovascular risk and familiarity with endoscopic anatomy, and recommended mastery of each level before moving to the next.

Implications for clinical practice

The choice of approach depends on the lesion's pathology, relationship to the midline, lateral extension and neurovascular relationships; endonasal and transcranial routes can be complementary rather than alternatives.
The reconstruction plan should be made before surgery; if intradural dissection is anticipated, a vascularised flap and, where needed, lumbar drainage should be considered in advance.
Patients should be clearly informed about signs of CSF leak (unilateral clear nasal discharge, headache, fever) and about the crusting period.

Limitations and currency note

The rates given here come largely from retrospective series of a single experienced centre and a single randomised trial; their generalisability is limited and results may differ between centres. Because modular classifications and reconstruction techniques continue to evolve, current literature and guidelines should be followed. This text is not a treatment recommendation for an individual patient; the final decision is made through multidisciplinary assessment.

Frequently asked questions

No. Small, low-flow defects can often be repaired with grafts. A vascularised flap is recommended especially for large dural defects, high-flow leaks and when postoperative radiotherapy is anticipated.

High-level direct comparative evidence is limited. In appropriately selected midline lesions it has the advantage of avoiding brain retraction, but for lesions with lateral extension a transcranial or combined approach may be more appropriate.

Sources

The general information on this page is based on the guideline and institutional sources below. Individual diagnosis and treatment decisions require an examination.