Idiopathic Intracranial Hypertension
Pseudotumor cerebri or idiopathic intracranial hypertension is a poorly understood condition. The fluid (the CSF or cerebrospinal fluid) that bathes and protects the brain, spinal cord, and optic nerve (the neural connection from the eye to the brain) accumulates faster than it drains causing the pressure of the CSF to rise. Normally, this pressure is less than 200 mm (or 20 cm) of water as measured by a spinal tap (LP or lumbar puncture). High CSF pressures often cause headaches. In some individuals, the increased CSF pressure may cause double vision, visual field loss, and blindness.
Pseudotumor cerebri is treated first with medications, often under the management of a neurologist or neuro-ophthalmologist. Diamox and Lasix (diuretics or “water pills”) are commonly used. Oral and intravenous corticosteroids may also be used. If the medications do not adequately control the disease or a patient is unable to take these medications, then surgery may be considered.
Reasons to consider surgery include:
- Debilitating headaches that can not be controlled with medical therapy.
- Vision or visual field loss.
- The threat of or impending severe vision loss.
Severe headaches are often best treated by a synthetic shunt (VP or LP shunts) implanted by a neurosurgeon. This is a tube that allows the CSF to drain into the abdomen. Vision loss may be treated by either a shunt or an optic nerve sheath fenestration (ONSF).
Optic Nerve Sheath Fenestration (ONSF)
The eyes are connected to the brain by nerves called optic nerves. The optic nerves are delicate structures that can be damaged by a high CSF pressure. Optic nerve sheath fenestration (ONSF) is a microsurgical procedure developed to protect the optic nerves. Although quickly performed (less than one hour), ONSF surgery requires considerable skill, knowledge, and experience.
The surgery is performed under general anesthesia through an eyelid crease incision less than an inch long. Dr. Klapper utilizes an eyelid approach which permits less dissection and disturbance of the eyelid, eye muscle, and orbital tissues. Through careful dissection, the optic nerve is identified and utilizing specialized instrumentation a small window is cut in the covering of the optic nerve. The CSF can then escape through this window where it is absorbed by the surrounding tissue.
In most cases, only one nerve is operated on at a time. About 1/3 of patients require fenestration on only one side. This will usually become apparent within 6 weeks of the first surgery. Many patients regain some vision with this surgery (if surgery is performed before permanent damage has occurred due to long-standing, inadequately treated disease). Some patient’s vision will stabilize, and in some cases vision loss will progress after ONSF surgery. Up to 50% of patients will have improvement in their headaches following ONSF. Walking, reading, and other non-stressful activities may be performed the day after surgery. Strenuous activities should be avoided for 10-14 days.
As with any surgery involving the eye and surrounding structures, there are considerable risks. With ONSF the risks are rare but potentially serious. Infection (with spread to the brain), bleeding behind the eye, and partial or complete vision loss are all possible. Change in pupil size can occur but is infrequent. A special contact lens can help camouflage pupillary irregularities.
So knowing that there are significant surgical risks, when should ONSF be performed?
Most eye specialists would agree that if there is clear evidence that vision is being lost, and a patient is taking as much medicine as they can safely take, then an ONSF operation should be considered. Many physicians also argue that if there is no vision loss, but the CSF pressure is high and the optic nerves appear swollen (seen by looking in the eye with an ophthalmoscope) despite medical therapy, or there are hemorrhages (bleeding episodes) within the eye near the optic nerve, then an ONSF procedure should be considered before potentially permanent vision loss occurs. In the end, the final decision on whether to proceed with surgery must be made by an informed patient. We encourage all of our patients to learn as much as they can about their disease and to discuss their medical situation with their ophthalmologist and/or neuro-ophthalmologist.