Anterior Skull Base Approaches

Anatomy of the Anterior Skull Base

• Anterior ethmoidal artery — lies posterior to the frontal recess, sometimes "slings" down as a pedicle within the ethmoid; retraction into the orbit causes acute orbital hematoma and blindness
• Posterior ethmoidal artery — lies just anterior to the sphenoid sinus
• The skull base is highest anteriorly and slopes downward posteriorly — dissection should proceed from posterior to anterior once the skull base is identified

Overview of Surgical Approaches

"For anterior cranial base lesions, the most commonly used open approaches employ some form of frontal craniotomy (unilaterally or bilaterally) with some form of transfacial exposure (transnasal, transmaxillary, or transorbital)."

1. Open Craniotomy-Based Approaches

Anterior Craniofacial Resection (ACR)

• Bifrontal craniotomy (intracranial component — neurosurgeon)
• Transfacial exposure (extracranial component — usually lateral rhinotomy ± contralateral Lynch incision, or midfacial degloving)

1. Transfacial exposure first — periosteum elevated from nasal bones and medial/inferior orbit; naso-lacrimal duct identified and transected; anterior and posterior ethmoidal arteries cauterized/clipped
2. Bifrontal craniotomy — if large frontal sinus, an osteoplastic flap is used; if small, a frontal bone flap with bur holes above the hairline
3. Frontal lobe elevation — dura incised and olfactory nerves severed at the cribriform plate; dural closure made watertight (temporal fascia, fascia lata, or pericranium)
4. Planum exposure — dura elevated to expose orbital roofs and planum sphenoidale; if disease involves the planum, optic canals are unroofed to protect intracranial optic nerves
5. En bloc ethmoidectomy with osteotomies using sagittal saw; orbital exenteration added if orbital soft tissue invasion confirmed

• Placed in the true coronal plane at the level of the top of the helix (or slightly anterior)
• Preserves anterior branches of the superficial temporal artery
• High placement maximizes length of vascularized pericranial flap available for reconstruction
• Lateral elevation in subgaleal plane, with an interfascial incision at the temporal lines to protect the frontal branch of the facial nerve

Keyhole / Supraorbital Craniotomy

• Craniotomy centered anterolaterally at the orbital roof/anterior fossa floor
• Incisions: transciliary, supraciliary, upper blepharoplasty, or transpalpebral
• Orbital osteotomy (Raza modification): increases visualization, limits frontal lobe retraction, expands working space; transpalpebral incision avoids frontalis palsy
• Access: anterior fossa, parasellar region, interpeduncular cistern
• Advantages: no facial scar, minimal brain retraction, wide exposure

2. Craniofacial Disassembly Techniques (Historical / Selected Cases)

• Le Fort I and II osteotomies, maxillary splitting
• Removal of the frontonasal unit
• Midfacial degloving with sublabial incisions

3. Endoscopic Endonasal Approaches (EEA)

Sagittal Plane Modules for Anterior Skull Base

Coronal Plane Modules

EEA Surgical Setup

4. Algorithm for Approach Selection

• Tumor involves overlying skin, nasal bones, frontal bone, or orbital soft tissue?
  • No → endoscopic approach feasible
    • No intracranial extension → Endoscopic alone
    • Intracranial extension, medial to orbital wall, adequate nasoseptal flap → Endoscopic alone
    • Intracranial extension, extension lateral to medial orbital wall → Endoscopic + Craniotomy
  • Yes → open transfacial required
    • No intracranial extension → Transfacial
    • Intracranial extension → Transfacial + Craniotomy

Contraindications to Purely Endonasal Approach

• Involvement of nasal bones or anterior table of frontal sinus
• Overlying skin of nasal dorsum or frontal sinus
• Orbital involvement requiring exenteration
• Need for vascular reconstruction
• Relative: expected very long operative duration

Summary Table: Anterior Skull Base Approaches

Transsphenoidal Approach to the Anterior Skull Base

Overview

"The great majority of the transnasal endoscopic skull base operations directly involve the sphenoid sinus, which is the focal point for several of the surgical approaches."

Methods of Sphenoid Sinus Access

1. Direct Transnasal Access

• Performed through one nostril
• Septoplasty first if nasal cavity is narrow
• Superior turbinate removed with through-cutting forceps; posterior middle turbinate also removed if access remains narrow
• Sphenoid ostium identified → opened with micro-Kerrison punch → enlarged inferiorly (avoiding the septal artery on the anterior wall)
• Both sphenoid sinuses exposed: anterior wall, rostrum, and all intersinus septa resected with semicutting or diamond burs

2. Transseptal Access

• Provides midline access through the nasal septum — specifically designed to avoid the lateral sphenoid wall, ICA, and optic nerve
• Submucoperichondrial/submucoperiosteal infiltration with ropivacaine 0.75% + epinephrine 1:100,000 (hydraulic dissection)
• Vertical hemi-transfixion incision at the caudal septal edge → septal flaps elevated (as in septoplasty)
• Osseocartilaginous junction disarticulated; posterior septal bone resected with Jansen-Middleton forceps
• Mucoperiosteum of anterior sphenoid wall elevated bilaterally; sphenoidotomy made with Kerrison punch enlarged with 5-mm diamond bur — large enough for simultaneous 4-mm endoscope + instrument

3. Transseptal-Transnasal (Binostril) Access (Stamm et al., 2008)

• Enables two-surgeon, four-hand technique without septal perforation
• Middle turbinates compressed and outfractured laterally
• Septal hemi-transfixion incision made → nasoseptal flap harvested on one side and stored in nasopharynx
• Contralateral septal mucosa kept intact (Fig. 177.15)
• Creates a wide bilateral working corridor through both nostrils simultaneously

4. Transnasal + Transethmoid Access

• Combines nasal and ethmoid corridors
• Used when disease involves both ethmoid and sphenoid sinuses, the ethmoid roof, or orbits

Transsellar and Parasellar Phase (Pituitary Fossa Opening)

• ICA prominences (bilateral)
• Optic nerve canal prominences (bilateral)
• Optic-carotid recesses (OCR)
• Planum sphenoidale (superiorly)
• Clivus (inferiorly)
• Floor of the sella turcica (centrally)

1. All intersinus septa resected with strong through-cutting forceps
2. Mucoperiosteum over sellar floor displaced laterally and preserved for reconstruction
3. Wide sellar bone resection with diamond bur + Kerrison punch — from ICA to ICA (lateral) and from planum to clivus (superoinferiorly)
4. U-shaped dural incision made after confirming locations of cavernous sinuses, superior/inferior intercavernous sinuses, and ICAs
5. Dura removed with attached tumor fragments (sent for histopathology)
6. Tumor resection begins laterally using 45° angled endoscope + curved suction; dissection is more important than curettage
7. Arachnoid (diaphragma sellae) = limit of superior/posterior dissection

Closure and Reconstruction

Extended Transsphenoidal Modules

Summary: Approach Selection by Target

1. Anatomy — Keros classification table, key surgical landmarks (ethmoidal arteries, skull base slope)
2. Overview of Approaches — spectrum from open to endoscopic
3. Open Craniotomy-Based Approaches — Anterior craniofacial resection (full step-by-step), supraorbital/keyhole craniotomy, craniofacial disassembly
4. Endoscopic Endonasal Approaches (EEA) — Sagittal plane modules table, coronal plane modules, surgical setup, contraindications
5. Transsphenoidal Approach — All four access methods (direct transnasal, transseptal, binostril, transethmoid), transsellar/parasellar phase with operative steps, closure/reconstruction table (Triple-F technique), extended modules table
6. Summary Tables — All approaches at a glance, approach selection by target region
7. 4 intraoperative/radiologic figures from Cummings embedded with captions