_{What is Optic Nerve Sheath Fenestration?}

An optic nerve sheath fenestration is a procedure now performed almost exclusively to treat patients with pseudotumor cerebri. Pseudotumor cerebri is a condition of unclear etiology (cause) which occurs primarily in young overweight females. The sine qua non of this condition is increased intracranial pressure in the absence of other contributing conditions, such as intracranial tumor.

Patients with this condition typically present with intractable headaches and may even have vision loss due to chronic or severe papilledema (swelling of the optic nerves). Patients who fail to have a significant or incomplete response to medical management and, perhaps, weight loss, are often referred for surgery. In general, a neurosurgical procedure, known as a ventriculo-peritoneal (V-P) shunt or lumbo-peritoneal (L-P) shunt is recommended for patients who primarily suffer from headache. Patients who primarily suffer from papilledema and vision loss may be good candidates for an optic nerve sheath fenestration.

Occasionally, a unilateral optic nerve sheath fenestration procedure will result in bilateral reduction of optic nerve edema. However, if a unilateral procedure is completed, and fails to result in bilateral resolution of papilledema, the opposite optic nerve will likely require the same procedure. An optic nerve sheath fenestration does not produce substantial lowering of intracranial pressure, and therefore, will not typically result in resolution of headaches if this is a characteristic of the syndrome.

An optic nerve sheath fenestration is usually performed bilaterally (both eyes) under general anesthesia. The surgeon creates access to the optic nerves via an orbitotomy, which is an incisional approach to the eye socket. The surgeon may proceed either medial or lateral to the eye itself. Once the surgeon gains access to the optic nerve itself, a small “window” is created in the optic nerve sheath using delicate instrumentation. Once the optic nerve sheath fenestration is created, cerebrospinal fluid (CSF) will begin to drain from the optic nerve sheath via the window, thereby releasing pressure on the nerve. This procedure results in reversal of optic nerve swelling and at least partial recovery of optic nerve function in most cases.

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