Tuesday, February 7, 2023
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Optic Nerve Sheath Fenestration

Overview

Introduction

Optic nerve sheath fenestration (ONSF) procedures were first described by De Wecker in 1872 as an incision in the meninges surrounding the optic nerve in order to relieve elevated intracranial pressure.
The procedure is typically performed in instances of papilledema due to idiopathic intracranial hypertension (IIH), in which the main symptom is rapid and/or progressive vision loss rather than headache. The effect is normally limited to the ipsilateral optic nerve, although occasionally the procedure appears to have a filtration effect, which is propagated along the entire system, resulting in improvements in headaches and contralateral disc edema as well.
Typically however, the effect is limited to the ipsilateral optic nerve.

The image below depicts optic nerve sheath fenestration.

Incision of the dura arachnoid is made with a long

Incision of the dura arachnoid is made with a long-handled 15º blade once careful visualization is made with retraction. Cotton-tip applicators are gently used for hemostasis.

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Although the procedure is most commonly performed for vision loss due to idiopathic intracranial hypertension, some cases exist of successful stabilization or reversal of vision loss due to optic nerve sheath hemorrhage, cryptococcal meningitis with papilledema, and intracranial breast cancer metastases with papilledema.
This procedure has not proven to be helpful in treating vision loss due to anterior ischemic optic neuropathy.

A small study in the pediatric population showed efficacy of optic nerve sheath fenestration similar to that in adults.

IIH is also referred to as pseudotumor cerebri. It is a disorder of unknown etiology that must meet the following criteria:

Signs and symptoms of increased intracranial pressure (headache, nausea, transient visual obscurations lasting seconds, double vision, dizziness, emesis)

Elevated cerebrospinal fluid (CSF) pressure (>200 mmHg in nonobese adults and >250 mmHg in obese adults)

Normal neuroimaging studies

Normal neurologic examination (with the exception of papilledema and/or cranial nerve palsies)

No other identifiable cause such as medications (including vitamin A, tetracycline, oral contraceptive pills, nalidixic acid, lithium, steroid use, or withdrawal)

IIH usually occurs in obese females 20-45 years of age.

Key considerations

Patients must undergo a complete ophthalmic history, neurologic examination, and an ophthalmic examination including visual acuity, color vision, pupillary assessment, motility, visual field testing, and funduscopic examination to evaluate for presence and extent of papilledema (swelling of optic nerve). Emergent neuroimaging (CT scan or MRI) should be performed to rule out any intracranial processes such as dural sinus thrombosis, which can result in papilledema. Lumbar puncture must be done to check the CSF composition and opening pressure. Blood pressure should also be recorded.

Medical treatment of idiopathic intracranial hypertension should be instituted, including weight loss, acetazolamide or furosemide, and systemic steroids if needed. If vision loss continues despite these measures, ONSF should be considered. Preoperative discussion should include reviewing the risks of orbital surgery in such a proximity to the optic nerve and the need for continued treatment of the underlying disease process, as this procedure is not a cure for the disease. If bilateral vision loss is present, the eye with more severe vision loss should undergo the procedure first.

Indications

Indications include idiopathic intracranial hypertension with rapid or progressive vision loss.

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