Introduction
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Transconjunctival and endonasal approaches provide direct access to the anterior skull base and can be employed in the surgical treatment of various pathologies.
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The combined transconjunctival and endonasal approach is a two-surgeon/four-handed technique designed to circumferentially access the anterior cranial fossa from both transcranial and transnasal trajectories in a minimally invasive fashion.
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The combined approach is associated with enhanced visualization, working area and angles of attack in the anterior skull base and it allows the surgeon to overcome the limitations of either approach alone. Combination of the two minimally invasive approaches may reduce the overall surgical morbidity and mortality.
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The combined approach is ideal for accessing pathologies that are situated anteriorly along the anterior cranial fossa that are in the midline with lateral extension over the orbital roof.
Indications
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Midline anterior skull base tumors involving the nasal cavity and/or the paranasal sinuses.
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Anterior skull base tumors with extension over the orbital roof or into the intraorbital space.
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Cerebrospinal fluid (CSF) leak due to the fovea ethmoidalis or planum sphenoidale defects.
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Blowout fractures of the orbital floor.
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Orbital tumors.
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Optic nerve tumors.
Contraindications
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Severe sphenoid sinusitis.
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Ecstatic midline carotid arteries.
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Hyphema.
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Ruptured globe or ipsilateral blindness.
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Small or asymmetric sellae (relative).
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Tumors with firm consistency (relative).
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Failed previous endonasal endoscopic surgery with significant alteration in normal anatomy.
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Intraocular surgery within the last 6 months, orbital inflammation, congestion, or infection.
Preoperative Considerations
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Detailed review of the medical history and physical examination are critical for differential diagnosis, patient selection and surgical planning.
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Preoperative computed tomography (CT) should be obtained to assess the bony anatomy of the paranasal sinuses and the anterior cranial fossa.
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Preoperative magnetic resonance imaging (MRI) with and without contrast is recommended to delineate the sellar anatomy and the relationship of the lesions to the surrounding structures, such as the optic chiasm, cavernous sinus and internal carotid arteries. Intensity of the lesion on T2 may correlate with the consistency of the tumor (i.e. hyperintense lesion may be soft whereas hypo- or isointense lesion may be firm and fibrous). Also, MRI can assist in preoperative diagnosis of the lesion of interest.
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An image-guided system can be used for intraoperative navigation.
Surgical Procedure
Patient Positioning
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After induction, the patient is placed in a Mayfield headholder with the head slightly extended at 15–20° for ease of access to the anterior fossa.
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The patient’s head must be rotated in such a way that the surgeon is working directly perpendicular to the floor, allowing the endoscope an insertion angle of approximately 25°.
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The level of the patient’s head must be placed higher than the level of the heart to keep cavernous sinus venous pressure low, thereby minimizing venous bleeding.
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To aid in local anesthesia and hemostasis for the endonasal approach, we suggest using a long hand-held nasal speculum and endoscope to delineate and infiltrate the nasal mucosa with 0.25% lidocaine and epinephrine (1 : 200 000).
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Meanwhile the transconjunctival approach is also prepared:
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A corneal shield is placed, and then the face and nose are prepared in a standard and sterile fashion.
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The conjunctiva, upper eyelid and medial canthal region are infiltrated with anesthetic and the lacrimal glands are protected with small probes.
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Incision
Transconjunctival Approach
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An incision is made with a No. 10 blade in the conjunctiva medial to the caruncle ( Figure 29.1 ) and extended superiorly and inferiorly following the posterior limbs of the medial canthal tendon to the posterior lacrimal crest ( Figure 29.2 ).
