Trans-nasal Endoscopic Skull Base Surgery (TNESBS)

1. Introduction / Definition

2. Advantages over Open/Craniofacial Approaches

• Avoidance of large transfacial and scalp incisions -> no facial scars
• Better visualization through magnification and angled scopes
• Avoidance of brain retraction
• Reduced surgical morbidity and blood loss
• Shorter hospital stay, faster recovery, improved quality of life
• Wide exposure with minimal trauma to normal tissue

3. Relevant Anatomy

• Anterior - anterior wall of sphenoid sinus
• Posterior - middle third of clivus
• Superior - planum sphenoidale
• Inferior - floor of sphenoid sinus
• Lateral - optic nerve, lateral optico-carotid recess, cavernous sinus, parasellar carotid artery

• Sellar type (75%) - most common, pneumatization extends below sella to clivus
• Presellar type (24%) - pneumatization does not extend beyond the anterior sellar wall plane - landmarks harder to identify
• Conchal type (1%) - solid bone block, no pneumatization

• Tuberculum recess - junction of anterior sellar wall and planum sphenoidale
• Medial optico-carotid recess - where tuberculum recess meets optic nerve (site of middle clinoid)
• Lateral optico-carotid recess - junction of optic nerve and anterior genu of carotid artery (site of optic strut/anterior clinoid)
• Clival recess - junction of clivus and pituitary fossa
• Optic strut - bone separating optic foramen from superior orbital fissure; oculomotor nerve lies close to lateral optico-carotid recess here
• Onodi cell - a posterior ethmoid cell pneumatized posteriorly into the sphenoid; the optic nerve may run within it, putting it at risk during sphenoid surgery

4. Indications

5. Contraindications

• Orbital involvement
• Involvement of the far lateral maxillary sinus
• Dural involvement lateral to the orbit
• Invasion of brain parenchyma
• Cavernous sinus or carotid artery involvement
• Lesion lateral to the cavernous carotid or superolateral to the optic nerve

6. Surgical Technique (Standard Transsphenoidal Steps)

1. Correct significant septal deviation via Killian/hemitransfixion incision so both nasal cavities can be used bilaterally.
2. Lateralize or remove middle turbinates bilaterally; identify superior turbinate and remove its lower two-thirds.
3. Identify the sphenoid ostium (just medial to the superior turbinate); make a horizontal mucosal incision from the ostium's lower edge, angled superiorly on the septum - this protects the posterior septal artery (for a nasoseptal flap if later needed).
4. Widen the sphenoid ostium bilaterally and inferiorly for instrument passage under the pituitary fossa floor to the clival recess.
5. Remove the posterior 1 cm of septum and enlarge the sphenoid ostium up to the lateral sinus wall, allowing lateral access to the carotids and optic nerves bilaterally.
6. Remove sphenoid sinus mucosa medial to lateral, leaving it pedicled laterally/inferiorly.
7. Remove the intersinus septum flush with the pituitary fossa; drill the anterior sellar wall thin if thick, until soft, then remove.
8. For extended (tumor) approaches: harvest nasoseptal flap and park it in the nasopharynx first; debulk tumor endonasally; perform maxillary antrostomies/ethmoidectomy/sphenoidotomy for landmark identification; resect bone (frontal sinus floor, orbital medial wall, sphenoid roof, septum) as needed for margins; ligate anterior/posterior ethmoidal arteries at skull base; open dura around the tumor with margin; transect olfactory roots if needed; confirm margins with frozen section.

7. Reconstruction / Skull Base Closure

• Multilayered reconstruction uses both inlay (underlay) and onlay (overlay) grafts:
  • Inlay grafts (between dura and skull base): abdominal fat, acellular dermis, fascia lata
  • Onlay grafts (extracranial): avascular grafts or pedicled vascularized flaps (nasoseptal flap, turbinate flap, pericranial flap)
• Vascularized flaps have a lower leak rate than free grafts, lower donor site morbidity, and faster healing.
• Small defects (<1 cm) can be repaired with any multilayer technique with >90% success.
• Reconstruction is buttressed with nasal packing; nasal trumpets or, rarely, tracheostomy can divert airflow and reduce pneumocephalus risk.

• Vertical incision parallel to the anterior inferior turbinate; superior incision starts at the inferior sphenoid ostium edge, running below the septum's superior edge; inferior incision runs along the posterior choana, free septal edge, and maxillary crest.
• Elevated as a mucoperichondrial flap, mobilized into the nasopharynx or maxillary antrostomy, then rotated to cover the defect.
• Blood supply: posterior septal branch of the sphenopalatine artery.
• A "rescue" nasoseptal flap (limited superior incision) can be pre-planned in cases where intraoperative CSF leak is only a possibility, preserving the vascular pedicle in case a full flap is later needed.

8. Complications

• Postoperative CSF leak - the most common complication; risk reduced substantially (to ~5%) by vascularized flap reconstruction.
• Tension pneumocephalus - less common than with open approaches; presents with rapid neurological decline, confusion, loss of consciousness.
• Perioperative bleeding - venous to carotid injury; managed with warm irrigation, gelfoam/thrombin packing, Floseal, cautery, or aneurysm clipping.
• Carotid artery injury (rare but life-threatening) - immediate tamponade with a pattie plus muscle graft (harvested from neck/thigh) placed over the injury, covered by a nasoseptal flap and gentle packing, followed immediately by interventional radiology for angiographic assessment.
• Cerebrovascular accident - from direct vascular injury, venous infarct (due to abrupt CSF pressure changes), or embolism.
• Infectious complications - rare, usually from postoperative crusting harboring bacterial overgrowth.
• Minor complications - sinusitis, vestibular (nasal) burns, anosmia, synechiae.

9. Recent Evidence (for context)

• A 2024 systematic review/meta-analysis on tissue sealants in skull base reconstruction found they influence CSF leak rates when combined with standard multilayer closure (PMID: 38470297).
• A 2024 review on the learning curve in endoscopic transsphenoidal skull base surgery highlights that complication rates fall significantly with surgeon experience and case volume (PMID: 38705991).
• A 2024 review of quality-of-life outcomes after anterior skull base surgery supports the functional advantages of endoscopic over open approaches (PMID: 38431213).

10. Summary (exam recall points)

• Gold standard for sella and expanding to whole ventral skull base (crista galli to foramen magnum, per Kassam's modules).
• Best for midline lesions; avoid if lateral to cavernous carotid, orbital, or brain parenchymal invasion.
• Key landmarks: optico-carotid recesses, clival recess, optic strut, Onodi cell.
• Closure = multilayer (inlay + onlay), nasoseptal flap is workhorse vascularized flap (supplied by posterior septal artery).
• Most common complication = CSF leak; most feared = carotid injury.