There are a variety of different techniques that can be used to surgically manage anterior skull base lesions. In this chapter we demonstrate the value of the standard and extended subfrontal craniotomies.
Indications
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The subfrontal approach allows access and excellent visualization to the majority of the anterior cranial fossa floor. This includes vital structures adjacent to the anterior midline and parasellar regions such as the tuberculum sella, anterior communicating artery, optic chiasm and optic nerves, posterior orbit, orbital apex and the internal carotid arteries.
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With appropriate pre-surgical management, minimal cerebral retraction is required, reducing the potential retraction-related cortical injury. With a bilateral orbital osteotomy, the extended subfrontal approach allows decompression of the optic nerves bilaterally, and increases the clival exposure while brain retraction is minimized. The expanded subfrontal approach is indicated in smaller and more posterior lesions (those that would require extensive fontal lobe retraction without the elevation of the supraorbital osteotomy) or those lesions with substantial superior extension.
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Both approaches provide a large and direct surgical view allowing en bloc resection of craniofacial malignancies that require negative margins for optimal oncological control. In such cases the subfrontal/extended subfrontal can be combined with a transfacial or endoscopic approach depending on the extension of the tumor to the soft tissues (transfacial preferred when soft tissue is involved) (see Chapters 28 and 30 ).
Potential Contraindications
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Patients with less extensive lesions that can be accessed through an endoscopic minimally invasive approach.
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Active sinonasal infection (infection can be spread after opening the frontal sinus to the intracranial space).
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Lesions located in the middle cranial fossa can be difficult to access using the bifrontal approach and therefore it is not indicated in such circumstances. Lesions positioned retrochiasmatically and subchiasmatically are preferably approached via a lateral exposure instead (e.g. pterional, orbitozygomatic osteotomy).
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However, the bifrontal/extended bifrontal approach can be combined with an orbitozygomatic osteotomy for anterior skull base tumors that are also extending posteriorly or to the temporal fossa.
Preoperative Considerations
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Preparation prior to surgery to reduce the intracranial pressure will allow reduced retraction. Intravenous mannitol, furosemide, steroid boluses (and antibiotics) as per protocol will also aid this. In some extreme cases this can be achieved by placing a lumbar drain, or external ventricular drain (EVD) if necessary, to bypass CSF as well as elevating the head above the level of the heart.
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These approaches allow harvesting of a pericranial flap for closure of the clival dura mater and anterior skull base reconstruction.
Surgical Procedure
Patient Positioning
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The patient is placed in a supine neutral position ( Figure 20.1 ). Alternatively, the chest can be slightly flexed with head extended. The three-pin headset is then placed.
Figure 20.1
Patient in supine position.
Reproduced with permission from Jandial, R., McCormick, P., Black, P. (Eds.), Core Techniques in Operative Neurosurgery. Saunders, Elsevier Inc., Philadelphia.
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Draping of towels is done in the standard meticulous way, with special consideration given to forehead draping to avoid creating excess pressure on the skin when the skin flap is turned forward (risk of flap ischemia).
Skin Incision
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The area around the skin incision is injected with local anesthesia. Supraorbital nerve block can be also useful ( Figure 20.2 ).
Figure 20.2
Patient position and skin incision.
© A. Quiñones-Hinojosa.
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Using a scalpel, a bicoronal scalp incision is made without incising the pericranium.
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The bicoronal incision is made posterior to the bregma extending to the zygomatic roots bilaterally.
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The incisions starts 0.5 cm anterior to the tragus (at the preauricular crease) bilaterally, extending it over the zygomatic root and then superior and anteriorly behind the hairline in a C-shaped fashion. At the sagittal midline the incision can be done with an anteriorly directed peak ( Figure 20.3 ).
Figure 20.3
Supraorbital nerve block.
© A. Quiñones-Hinojosa.
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The superficial temporal arteries are preserved bilaterally.
Deep Tissue Dissection
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The scalp is elevated preserving the vascular pericranium for posterior reconstruction. The anatomical landmarks that are exposed are the supraorbital rim bilaterally and the glabella.
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Careful dissection is required over the temporalis muscle since the superficial temporal fat pad needs to be elevated separately to preserve the frontal branches of the facial nerve.
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The fat pad, which is superficial to the temporalis fascia, is elevated with care with a curvilinear incision and using a subfascial technique to preserve the frontalis branch of the facial nerve ( Figure 20.4 ).
Figure 20.4
The superficial temporal fat pad is elevated with a separate flap to preserve the frontal branches of the facial nerve.
© A. Quiñones-Hinojosa.
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The scalp is reflected forward over the superior orbital rim. A cushion made with gauzes can be placed below the skin flap to avoid a steep curvature of the flap that may preclude optimal blood flow to the skin flap.
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A large rectangular-shaped pericranial flap is elevated. The base of the flap is at the orbital rims. The limits of the flap are the superior temporal lines bilaterally and the supraorbital ridge anteriorly. The flap is reflected anteriorly and well moisturized throughout the surgery ( Figure 20.5 ).
Figure 20.5
(A, B) View of the subfrontal craniotomy pericranial flap, maintaining adequate length and good vascular supply to further use it for reconstruction of the skull base defect.Related posts:
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