Abstract
Endoscopic transnasal surgery has become an effective approach to the surgical management of diseases of the sinuses, orbit, and anterior skull base. Technologic advances have been critical in advancing endoscopic surgical procedures, with the introduction of improved optics and lighting, advanced instrumentation, and image-guided surgical navigation.
Multiple approaches to the optic nerve have been described, ranging from endonasal endoscopic to open craniotomy. The endonasal endoscopic approach offers many advantages, which makes this the preferred method for optic nerve decompression. Advantages include: decreased morbidity, avoidance of external incisions, preservation of olfaction, superior visualization of and access to the optic nerve, rapid recovery, and decreased operative stress compared to open approaches, especially for trauma patients.
A close working relationship with an ophthalmologist or neuro-ophthalmologist is recommended. The surgical approach presented is familiar to the otolaryngologist, but experience is recommended before this procedure is attempted. The decision to proceed with medical rather than surgical treatment is controversial in many cases.
Keywords
decompression, endoscopic, optic nerve, orbital, rhinology, sinus
Introduction
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Endoscopic transnasal surgery has become an effective approach to the surgical management of diseases of the sinuses, orbit, and anterior skull base. Technologic advances have been critical in advancing endoscopic surgical procedures, with the introduction of improved optics and lighting, advanced instrumentation, and image-guided surgical navigation.
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Multiple approaches to the optic nerve have been described, ranging from endonasal endoscopic to open craniotomy. The endonasal endoscopic approach offers many advantages, which makes this the preferred method for optic nerve decompression. Advantages include avoidance of external incisions, preservation of olfaction, superior visualization, and access to the medial optic nerve.
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A close working relationship with an ophthalmologist or neuro-ophthalmologist is recommended. The surgical approach presented is familiar to the otolaryngologist, but experience is recommended before this procedure is attempted.
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Indications for this procedure are limited. The decision to proceed with medical rather than surgical treatment is controversial in many cases.
Anatomy
Orbit and Orbital Apex
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The extraconal space consists mostly of orbital fat encased within the periorbita.
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The intraconal space is located within the fascia of the extraocular muscles. It contains the muscles, retrobulbar fat, optic nerve, and ophthalmic artery ( Fig. 19.1 ).
Fig. 19.1
Drawing of the posterior orbit in coronal view. CN, Cranial nerve; n., nerve.
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The annulus of Zinn is the fibrous thickening formed by the fusion of the pia and arachnoid. This is the most constricting portion of the fibrous tissue around the nerve. It is also a site of attachment of the extraocular muscles.
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The superior orbital fissure is located superolateral to the optic foramen, and the inferior orbital fissure is located inferolateral to the foramen.
Optic Nerve
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There are four segments of the optic nerve: intracranial, intracanalicular, intraorbital, and intraocular ( Fig. 19.2 ).
Fig. 19.2
Drawing of the four portions of the optic nerve.
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The optic canal is formed by two struts of the lesser wing of the sphenoid. Within it are the optic nerve and ophthalmic artery. The intracanalicular segment is the target of optic nerve decompression surgery.
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The optic nerve is a direct extension of the brain, with its three meningeal layers and cerebrospinal fluid (CSF)–containing subarachnoid space. The dura splits to form an outer layer, which contributes to the periorbita, and an inner layer, which fuses to the arachnoid ( Fig. 19.3 ). The ophthalmic artery travels inferolateral to the nerve in 85% of cases and is located inferomedial to it in 15% ( Fig. 19.4 ).
Fig. 19.3
Drawing of the layers of the optic nerve.
Fig. 19.4
Drawing showing the relationship of the optic nerve to the ophthalmic artery. In 85% of cases, the ophthalmic artery runs inferolateral to the optic nerve. In 15% of cases, it runs inferomedial to the nerve. A., Artery; Ant., anterior; Post., posterior.
Sinus
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The transethmoid route to the sphenoid sinus provides the pathway to the optic nerve. The middle and superior turbinates, skull base, and lamina papyracea form the boundaries of this pathway.
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The sphenoid sinus may be variably pneumatized. In the lateral aspect of the sphenoid sinus, the optic nerve (superior) and carotid artery (inferior) impressions are usually visible, as is the opticocarotid recess ( Fig. 19.5 ).
Fig. 19.5
Endoscopic view of a left sphenoid sinus with optic nerve (white arrow) and carotid artery (black arrow) impressions on the lateral wall. The asterisk indicates the opticocarotid recess.
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An Onodi cell is a posterior ethmoid cell that pneumatizes superolaterally into the sphenoid. This cell will contain a portion of the optic nerve.
Indications and Contraindications for Optic Nerve Decompression
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Indications for optic nerve decompression include traumatic optic neuropathy, thyroid eye disease associated with optic neuropathy, vision loss secondary to idiopathic intracranial hypertension, fibro-osseous lesions, and other neoplasms (sinonasal tumor, meningioma, orbital apex tumor).
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Contraindications for optic nerve decompression include complete disruption of the nerve or chiasm, complete atrophy of the nerve, carotid-cavernous fistula, and other medical comorbidities precluding the use of general anesthesia.
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If appropriate, a trial of medical therapy should precede consideration of decompression. Decompression for traumatic optic neuropathy is considered controversial. Patients with severe vision loss not improved with high-dose steroid therapy may benefit from surgery.
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Timing of decompression is also controversial for traumatic optic neuropathy. In general, earlier decompression is associated with a higher chance of recovery of vision.
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