Indications
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The major advantages of this approach include broad exposure to the anterior cranial base with minimal brain retraction.
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The approach can facilitate the access to the anterior skull base, especially at the midline, including orbits, planum sphenoidale, sphenoid sinus, sphenoethmoidal and clival regions, as well as to the nasal and paranasal cavities with direct visualization of the adjacent vital structures.
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This combined approach is very useful for lesions at the sphenoid sinus and parasellar region that extend to the anterior cranial fossa. The endoscopic endonasal approach provides additional access, visualization and maneuverability to the ethmoidal cells, sphenoid sinus and frontal sinus.
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Management of anterior skull base fractures, defects and congenital anomalies.
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CSF leak repair.
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Treatment of extra-axial lesions, including chordomas, meningiomas, infectious and inflammatory disorders.
Contraindications
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Lesions that can be removed through only one approach, either endonasal or subfrontal.
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Patients that could not tolerate surgery due to medical conditions like advanced age with comorbidities or patients with several previous radiation treatments or advanced diabetes in which the healing process may be impaired.
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A lateral approach is better for retrochiasmatic and subchiasmatic lesions.
Surgical Procedure
Patient Positioning
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The patient is placed in the supine position with the body slightly elevated and the head is fixed with a Mayfield clamp, slight extension and contralateral rotation of approximately 30°, allowing the gravity effect on the frontal lobe. This 30° rotation positions the orbital rim horizontal to the floor and the maxilla is set as the highest point of the field.
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Careful positioning is required to allow neurosurgeons as well as ENT surgeons to work at the same time; the neurosurgeon will lead the subfrontal approach, while the ENT surgeon will proceed through the endonasal dissection.
Skin Incision
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Shaving of a 1–2 cm strip of hair behind the hairline for the skin incision which allows appropriate draping.
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A bicoronal skin incision is performed for the subfrontal approach. This starts at the level of the zygomatic arch, less than 1 cm in front of the tragus and extended to the other side. Care should be taken to preserve the facial nerve and its branches.
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A skin flap is elevated from the cranial vault to the supraorbital rim bilaterally, leaving the pericranium attached to the bone.
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Careful dissection is required at the inferior region of the bicoronal incision (in front of the tragus) since the superficial temporal artery runs through that area. An inadvertent lesion of this artery can produce profuse bleeding.
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A subfascial dissection is performed at the temporal fossa to elevate the temporal fat pad separately in order to preserve the facial nerve during the scalp flap elevation as one would do in the orbitozygomatic approach.
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In some cases a transbasal approach with bilateral or unilateral orbitotomy may be required. In those cases, the zygomatic arch is exposed and the temporal muscles are partially elevated. If a unilateral orbital osteotomy is planned, this maneuver can be performed on one side only.
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In a planned osteotomy, the periorbita is detached from the orbital roof to uncover the bone, avoiding laceration of the periorbita.
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To avoid damage to the supraorbital nerve, the supraorbital notch can be widened with a chisel or if the nerve is restrained by a bony foramen it can be freed with an osteotome.
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An anterior pediculated galea and pericranial flap is liberated and raised from the bone and ideally kept intact and in one piece.
Craniotomy
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For the subfrontal approach the craniotomy may include:
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Unilateral subfrontal approach or bilateral subfrontal approach: Frontal squama and the anterior portion of the parietal bones with or without the orbital bar.
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Transbasal approach: Includes the orbital rim, nasion and anterior part of the ethmoid bone. This can be extended to the orbital roof and lateralized to elevate part of the zygoma if required.
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Burr Holes ( Figure 28.1 )
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For the subfrontal craniotomy, several burr holes can be made. A burr hole is drilled in the midline facing the anterior third of the superior sagittal sinus (SSS). Two burr holes, one on each side of the SSS, may also be used.
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If the bilateral orbital osteotomy is planned, burr holes are placed at the right and left MacCarty keyhole.
