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Optic Nerve Sheath Fenestration vs Cerebrospinal Diversion Procedures

What Is the Preferred Surgical Procedure for the Treatment of Idiopathic Intracranial Hypertension Failing Maximum Medical Therapy?

Spitze, Arielle MD; Malik, Amina MD; Al-Zubidi, Nagham MD; Golnik, Karl MD, MEd; Lee, Andrew G. MD

Editor(s): Lee, Andrew G. MD; Biousse, Valérie MD

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Journal of Neuro-Ophthalmology: June 2013 - Volume 33 - Issue 2 - p 183-188
doi: 10.1097/WNO.0b013e318292d06f
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Although most patients with idiopathic intracranial hypertension (IIH) can be effectively treated with conservative measures, such as lumbar puncture, weight loss, acetazolamide, medical treatment of headaches, surgery is sometimes necessary, particularly in patients with visual loss secondary to chronic papilledema (1–4). Recently, endovascular venous stenting of a stenosed dominant intracranial transverse venous sinus has been proposed as a possible treatment (5); however, cerebrospinal fluid (CSF) shunting and optic nerve sheath fenestration (ONSF) remain among the most commonly used surgical procedures to treat IIH in the United States (6). In the absence of any prospective, randomized clinical trials comparing these procedures for the treatment of IIH, opinions vary greatly between ONSF and CSF shunting procedures as the most appropriate recommended surgical treatment (7,8). The decision to use one or the other is often based on local preferences and the availability of specific surgeons; some centers always perform ONSF as a first-line treatment, some use both procedures based on patient’s symptoms and signs (ONSF for visual loss and shunts for headaches), while others exclusively recommend lumboperitoneal shunt (LPS) or ventriculoperitoneal shunt (VPS) when surgery is necessary (9).

PRO—ONSF is the preferred treatment for IIH patients who require a surgical treatment. Arielle Spitze, MD, Nagham Al-Zubidi, MD, Andrew G. Lee, MD

Opening Statement:

In our experience, ONSF is superior to CSF shunting based on the following: 1) ONSF directly treats the major morbidity of IIH, namely, visual loss from chronic papilledema; 2) ONSF may also treat the headache of IIH; 3) ONSF has less morbidity (and mortality) than CSF shunting; and 4) CSF shunting has poor long-term efficacy and may require multiple revisions.

ONSF is the preferred treatment of visual loss in IIH

There are numerous reports demonstrating the significant visual improvement following ONSF in IIH patients who have experienced uni- or bilateral visual loss from papilledema. Banta and Farris (10) studied 158 eyes of 86 IIH patients undergoing ONSF. All but 7 patients underwent bilateral ONSF. A 94% improvement in visual acuity (148 of 158 eyes) and an 88% rate of visual field stabilization or improvement (71 of 81 eyes) were reported. Additionally, there was only 1 eye (less than 1% of the patients) that experienced any severe, vision-limiting surgical complications. Chandrasekaran et al (11) reported visual acuity and visual field (mean deviation) outcomes in 51 eyes of 32 IIH patients having ONSF. Patients with mild visual loss improved or stabilized, and patients with more severe visual loss stabilized postoperatively. Complications in this series were all self-limited (e.g., diplopia, anisocoria, disc hemorrhage) and resolved without further surgical or medical intervention. Spoor and McHenry (12) retrospectively studied postoperative ONSF outcomes in IIH in 75 eyes and reported 68% improvement or stabilization in visual function.

Interestingly, unilateral ONSF may not only result in ipsilateral improvement of papilledema and visual function but also lead to improvement in the nonoperated fellow eye. This was emphasized in a recent retrospective study of 62 IIH patients who underwent unilateral ONSF (13). Although the reduction in papilledema was greatest on the operated eye, a reduction in papilledema grade was also seen in the contralateral eye at 3, 6, and 12 months postoperatively. The reduction in papilledema correlated with a corresponding increase in visual function in both operated and contralateral eyes. In a retrospective literature review by Feldon (14), the majority of ONSF were bilateral (59%), although he emphasized that in patients with significantly asymmetric loss of vision, unilateral ONSF can be employed in the more severe eye first. Although bilateral ONSF might require 2 surgical sittings with separate anesthesia compared with a single anesthesia session in a CSF shunting procedure, bilateral ONSF may not always be necessary even in patients with bilateral visual loss and papilledema.

ONSF may improve headaches in IIH patients

In one review, a significant improvement in or resolution of headaches was reported in more than half of the patients with IIH after ONSF (15). Some studies support the finding of up to 50% improvement in headaches following ONSF (16,17), while Banta and Farris (10) reported improvement in 31% of their ONSF cases. The mechanism for this is unclear. One hypothesis is that the reduction in headache is related to reduced intracranial pressure (ICP) secondary to CSF drainage through the fenestration, although this mechanism is questionable given the small size of the sheath fenestration slits or windows. Alternatively, this may result from placebo effect with increased patient compliance with medical therapy. A prospective standardized evaluation of the sustainability of any treatment effect of ONSF on headache does not exist, and this makes it difficult to draw any meaningful conclusions on the pathogenesis or long-term efficacy.

ONSF has low morbidity and mortality

The ONSF procedure initially was described using a lateral approach with or without disinsertion of the lateral rectus muscle (17). However, many important vascular structures and nerves as well as the lacrimal gland are located laterally. A medial subconjunctival approach was devised and is commonly used today, although it also requires medial rectus disinsertion and/or significant medial rectus retraction, which can still lead to muscle or third nerve–related surgical complications. Another technique gaining popularity is using an anterior medial upper eyelid crease approach to gain access to the medial intraconal space (18). This approach offers a relatively avascular plane between the superior oblique and medial rectus muscles and fairly offers direct access to the retrobulbar optic nerve. Although the risk for nerve or muscle injury is still present, it is minimized because there is no need to disinsert any of the extraocular muscle or use significant heavy traction on the muscles.

It is difficult to compare ONSF complication rates among institutions and studies because of the many different surgical techniques. Most studies of ONSF have reported that surgical complications are usually transient and resolve without sequelae (9–11,14). Chandrasekaran et al (11) found a 15.6% overall complication rate (5 of 32 patients) after ONSF. All complications were self-limited (3 patients had diplopia, 2 had anisocoria, and 1 patient had a disc hemorrhage). In this study, all surgeries were performed by the same surgeon using a medial subconjunctival approach. Plotnik and Kosmorsky (19) reported a higher (40% overall) complication rate, including temporary motility disorders (29%), and pupillary dysfunction (11%), in addition to more severe vascular complications (11%) (1 episode of transient outer retinal ischemia, 1 superotemporal branch retinal artery occlusion, and 2 central retinal artery occlusions). Mauriello et al (20) identified 5 patients with poor outcome after ONSF including 1 postoperative retrobulbar hemorrhage, 1 infectious postoperative optic neuropathy, and 3 patients with a gradual decline in vision without a particular surgical complication identified (the mechanism was suspected to be persistently elevated ICP).

Although a wide range of complication rates were reported to be associated with ONSF, most studies are in agreement with a range between 5% and 45% (9). The large range is likely secondary to variable surgeons and ONSF techniques, as surgical procedures between institutions are often not standardized, or can differ between surgeons within the same institution. Even with such wide variability, severe complications remained rare, and no fatalities were reported.

CSF shunting procedures have high morbidity and mortality compared with ONSF

Shunt-related complications in a study by the Karabatsou et al (21) included 17 shunt migrations, 1 case of temporary radiculopathy, 7 shunt-related infections (1% infection rate per procedure or 33% per patient), and 7 patients with tonsillar herniation (although only 2 patients were symptomatic). El-Saadany et al (22), although reporting an improvement in headaches in the majority of their 22 patients, also reported a 9% (2 of 22) shunt infection rate, a 27% (6 of 22) rate of shunt obstruction, and a 13% (3 of 22) rate of shunt overdrainage.

El-Saadany et al (22) found that the migration of the peritoneal catheter was the most common cause for shunt obstruction and result in the need for shunt revision. Tarnaris et al (23) reported on 29 patients who underwent a shunt procedure. Of these patients, 20.5% (6 of 29) had complications, and 35% (10 of 29) ultimately required a shunt revision. Complications in this series included shunt infection, shunt obstruction, intra-abdominal pain, and CSF leak. LPS procedures (n = 24) were advantageous in avoiding intracranial complications but involved more problems with infection, subdural hematoma, cerebellar tonsillar descent, and distal catheter migration and obstruction. VPS (n = 5) had lower revision rates, but this may be because of the fact that far fewer VPS were performed than LPS. VPS have a greater risk of intracranial complications and difficulty with shunt placement within the small ventricles of IIH patients (23). Newer techniques such as stereotactic VPS placement have been introduced, which could lower shunt placement complications in the future. More long-term, prospective studies are needed to compare shunt placement techniques (24).

Between 1988 and 2002, the incidence of CSF shunting for IIH reported by Curry et al (25) increased up to 350% nationwide. While this study had limitation, out of 2,779 admissions for CSF shunting in IIH patients, overall inpatient mortality was 0.5% (0.9% mortality rate for VPS and 0.3% for LPS). Thus, our strongest argument against CSF shunting as the primary surgical option in IIH is the unacceptable mortality rate of up to 0.9% for what is a non-life-threatening condition and for which there is a reasonable surgical alternative, namely, ONSF. In addition, shunts often require an inpatient hospital stay, unlike ONSF, which are performed on an outpatient basis.

CSF shunts (VPS, LPS, and ventriculoatrial) have weaker long-term efficacy in IIH

A large literature review summarized the findings of 7 different retrospective series including a total of 423 eyes of 252 IIH patients post-ONSF. In a mean follow-up period of 21.1 months, the revision or reoperation rate was 12%, with only 4% ultimately requiring CSF shunting (20).

In contrast, Sinclair et al (26) found that shunt revisions were commonplace, with 51% of the patients requiring a revision and 30% requiring multiple revisions. This high rate may be secondary to the large number of primary LPS (49 of 53 patients). This type of shunt is reported to have a higher revision rate than VPS. It may also be surgeon and institution dependent. Although CSF shunting was found helpful in halting visual deterioration, Sinclair et al (26) suggested that because of the high rate of shunt complications, shunt revisions, and persistent postshunt headaches, headaches alone should not be an indication for shunting. Karabatsou et al (21) retrospectively reviewed the outcomes of 21 patients post-LPS placement and also reported high shunt revision rates. There was an average of 3 revisions per patient, with a total of 63 revisions in 21 patients over an average follow-up period of 24 months. Only 3 patients did not undergo shunt revision.

Despite decreasing ICP, CSF shunts do not always improve symptoms. This finding could in part be the result of the non-ICP-related nature of many IIH-associated headaches. In their 10-year review, Sinclair et al (26) reported an overall improvement in visual symptoms after shunting, but headaches remained in a majority of patients (79%). The lack of improvement in headache after shunting may be because of the fact that not all headaches in IIH patients are related to increased ICP.

In summary, we argue that ONSF is a superior surgical option to CSF shunting in IIH because 1) ONSF effectively treats the major morbidity of IIH, namely, the papilledema and related vision loss; 2) ONSF may also treat the headache of IIH; 3) CSF shunting has poor long-term efficacy in IIH and may require multiple shunt revisions; and 4) ONSF has less morbidity and less surgical procedure–related mortality (compared with up to 0.9% mortality for VPS) for a non-life-threatening condition.

CON—Cerebrospinal diversion procedures are the treatment of choice in patients with IIH failing maximal medical therapy: Amina Malik, MD, Karl Golnik, MD, MEd

Opening Statement:

We would argue that in patients with both headache and visual loss, CSF shunting is the preferred treatment for IIH. We make this argument based on the fact that 1) CSF shunting works to directly lower the ICP, which is the underlying problem in IIH patients; 2) CSF shunting, unlike ONSF, does not pose any direct risk to vision, which is what our treatment is aimed toward improving; and 3) patients who undergo ONSF may eventually require CSF shunting procedures.

CSF diversion procedures lower ICP and improve signs and symptoms of IIH

Shunting procedures (LPS or VPS) often result in the improvement of neurologic symptoms related to increased ICP, including headache, nausea, vomiting, memory loss, pulsatile tinnitus, or diplopia from sixth nerve palsy (27). In a retrospective review of 30 cases of IIH treated with LPS, Burgett et al (28) reported that 82% of their patients experienced improvement in the symptoms of increased ICP, including headache. There was an improvement of at least 2 lines of visual acuity in 71% of patients with preoperative decreased vision, including one patient who improved from no light perception to 20/25. Only 1 eye had worsened visual acuity, for which the patient previously had undergone ONSF. Twenty-eight patients had preoperative abnormalities on kinetic visual field testing, of which 18 patients showed improvement and none worsened. Papilledema resolved in 96% of patients. The most common complication was shunt revision, with a total of 126 revisions in 30 patients, with a mean revision rate of 4.2. However, 87 of these revisions occurred in only 4 patients. Excluding these patients, the revision rate was 2.5 per patient. As noted in previous series, the need for shunt revision was not distributed evenly among all patients but was concentrated in a subgroup of patients who seemed particularly prone to shunt failure. Shunt infection, the only life-threatening complication, occurred in only 1 of the 30 patients (28).

Eggenberger et al (29) reported a series of 27 patients with IIH treated with LPS. The indications for LPS were intractable headache in 18 patients (67%) and progressive optic neuropathy in 14 patients (52%). Visual function improved to normal in both eyes of 6 patients, had no change in either eye in 4 patients, and improved in at least 1 eye in the remaining 4 patients. Additionally, 5 patients had sixth nerve palsies, all of which fully resolved postoperatively. All patients in this study had improvement in neurologic symptoms, and no shunt-related symptoms, such as low-pressure headache or abdominal pain, were noted within 2 months of the surgery. Although 56% (15 of 27) of patients required shunt revision, there were no major complications from LPS other than shunt failure. Angiari et al (30) reported 3 cases of IIH with significant visual defects who underwent LPS. All 3 patients experienced visual recovery and alleviation of neurologic symptoms without any life-threatening complications. Similarly, McGirt et al (31) reported 42 patients with IIH who underwent 115 shunt placement procedures. Forty patients (95%) experienced a significant improvement in their headaches immediately after the shunt was performed. Abubaker et al (32) reported 25 patients who underwent shunting procedures. Eighteen patients underwent LPS, of which all experienced immediate postoperative improvement in visual acuity and visual fields. The majority (11 of 19) experienced improvement in headache and papilledema. Ten patients required shunt revisions. Other complications seen were radicular pain in 1 patient, abdominal pain in 2, low pressure headaches in 2, and shunt infection in 1 patient.

The study by Curry et al (25) (cited above) reported that the mortality in CSF diversion procedures is 0.9%, which is an initially alarming number. However, this is a review from a national hospital discharge database where no individual cases can be identified. It is unclear exactly why these patients died, and why the CSF diversions were performed. We know of no documented cases of death directly related to CSF diversion for IIH.

These studies suggest that LPS is an effective treatment for both visual and neurologic symptoms in IIH patients with a low rate of overall morbidity and mortality, with the main complication being shunt revisions. Nevertheless, shunt revisions have low morbidity and mortality, and thus, CSF diversion procedures benefits outweigh the downside of this complication.

ONSF can pose a direct threat to vision

While improvement in visual function and papilledema after ONSF has been well documented (10–13,19,33), this surgical procedure can pose a direct threat to vision. In the study by Plotnik and Kosmorsky (19), 2 of 38 patients (5%) had permanent visual loss from central retinal artery occlusion. Mauriello et al (25) reported 5 patients with IIH who underwent ONSF and had postoperative visual loss. One had an abrupt decrease in vision 6 days after the surgery, caused by bleeding from a vessel on the nerve sheath. This patient had a 20/20 vision 1 day postoperatively but decreased to 20/200 after five days. High-dose intravenous corticosteroids failed to improve vision, but emergency LPS resulted in full visual recovery. An infectious optic neuropathy developed in another patient 3 days after the surgery, although visual acuity did improve from 20/600 to 20/15 after 72 hours of intravenous antibiotics. The other 3 patients had gradual visual loss after ONSD, all of which stabilized after LPS. In an animal study by Gellrich et al (34), ONSF was performed on 22 rats and with a significant reduction in the number and size of retinal ganglion cells and amacrine cells 30 days after the surgery, compared to rats that did not undergo ONSF. Although ONSF is thought to have “low” risk, in patients with relatively good vision, even a 1% risk of permanent visual loss is too high. We argue that because vision preservation (and improvement) is the primary treatment goal in IIH patients, performance of a surgery with a direct threat to vision is less desirable than CSF diversion, which poses no direct risk to vision.

Patients who undergo ONSF may go on to require CSF diversion procedures

Headache is the most common symptom in IIH and present in 92%–94% of patients (8). While CSF diversion procedures have been documented to improve headaches (28–32), only 50% of patients who undergo ONSF will experience significant, persistent relief from headache (29). Banta and Farris (10) documented that only 31% of patients who underwent ONSF experienced improvement in headache. Even a 50% reduction in headaches is not adequate for patients debilitated by this symptom.

Additionally, patients who undergo ONSF may require future CSF diversion procedures to treat intractable visual loss (35). In a study by Acheson et al (35), 20 eyes of 14 patients underwent ONSF. Of these, 11 patients had IIH. Eleven eyes had reduced vision preoperatively, of which 5 improved, 3 stabilized, and 3 deteriorated. Four patients (20%) required additional CSF diversion surgery for persistent headache and/or visual loss. Herzau and Baykal (36) reported a long-term follow-up of ONSF in 23 eyes of 14 patients. Improvement or stabilization in visual acuity and visual field testing was documented in 17 eyes. Six eyes, however, showed a recurrence of papilledema after an interval of 7–121 months. Three eyes of 2 patients progressed to develop optic atrophy and extensive visual loss. In performing ONSF in 75 cases, Spoor and McHenry (12) found only 36% sustained improvement in visual function, 32% had stabilization, and 32% experienced deterioration. In their series, 24 eyes required repeat ONSF for decreasing visual function. Of these, 6 eyes had persistently decreased visual function and required either repeat ONSF or shunting procedure. In the cases that required yet another ONSF, extensive scarring and arachnoidal adhesions were found at the site of previous surgery, and these patients rarely enjoyed long-term improvement in visual function. Since many patients may end up requiring CSF diversion procedures after undergoing ONSF, we maintain that it is not worth subjecting patients with IIH to 2 surgeries, when CSF diversion procedures can alleviate both visual and neurologic symptoms.

In summary, we believe that in patients with IIH who present with neurologic symptoms and visual loss, CSF diversion procedures are preferred to ONSF because 1) CSF diversion procedures address the underlying problem and lower ICP, 2) ONSF can pose direct threat to vision, and 3) patients who undergo ONSF may go on to require CSF diversion procedures. We reserve ONSF for patients with rapid visual loss or progressing visual loss without headaches or other neurologic symptoms.

Rebuttal: Arielle Spitze, MD, Nagham Al-Zubidi, MD, Andrew G. Lee, MD

We offer the following point-by-point rebuttal to the advantages of shunting proposed by Malik and Golnik. First, they propose that CSF diversion procedures address the underlying problem of IIH by lowering ICP. This is true, but only if the shunt is functional. Our main contention with CSF shunting is that the effect may not be sustained and the long-term efficacy of CSF diversion procedures remains problematic. Second, although we acknowledge that ONSF can pose a direct threat to vision, so can shunting—both from failure of the shunt (shunt related visual loss) or from direct or indirect injury by the shunt catheter—shunt infection (e.g., meningitis related visual loss), or problems related to overdrainage. We also acknowledge that patients who undergo ONSF may still require a CSF diversion procedure. In fact, we believe that it is appropriate in some settings to have both procedures (fulminant IIH with severe and progressive visual losses). Malik and Golnik state that they have no direct knowledge of shunt-related mortality and question the nature of underlying etiologies for death from shunting in the study by Curry et al (25). In our referral practice, we see many patients with shunt-related complications that are potentially life threatening including shunt infection (bacterial and fungal), proximal or distal shunt obstruction, migration, disconnection, slit ventricle syndrome, overdrainage (with worsening of headaches), acquired Chiari 1 malformations, and both intraventricular and subdural hemorrhages. In addition, we speculate that some of the causes of mortality may be related to the more prolonged recovery time for CSF shunting vs ONSF and may increase the risk of deep venous thrombosis and pulmonary embolus. Other cases with morbidity or mortality after shunting may have included occult dural arteriovenous fistulas with venous sinus thrombosis mimicking IIH for which an LPS might create a dramatic ICP gradient change, tonsilar herniation, or autoregulatory failure at the disc head and worsening visual loss. Cognard et al (37) stated that an LPS in this setting would be contraindicated.

Rebuttal: Amina Malik, MD, Karl Golnik, MD, MEd.

First, we do acknowledge that while CSF shunting often requires revisions over time, the surgery still works by lowering the overall ICP, in contrast to ONSF. Even if revisions are performed, the surgery addresses the underlying problem of increased ICP in IIH. Second, we would still argue that CSF diversion does not pose a direct threat to optic nerve function. We know of no cases of direct vision loss because of the performance of a CSF diversion procedure, while cases of blindness after ONSF have been reported, as discussed above. Third, we acknowledge and have observed complications related to CSF shunting procedures, but unlike our colleagues, we have not experienced mortality as a complication of shunting.

Conclusion: Andrew G. Lee, MD and Valérie Biousse, MD

This debate confirms the need for a study directly comparing ONSF with CSF-shunting procedures in the treatment of IIH. In most cases, the decision to perform an ONSF or a CSF shunting procedure in a patient with severe IIH is based on local preference: some centers mostly have access to ONSF, whereas others do not have skilled surgeons able to perform a safe ONSF, and therefore choose a CSF shunting procedure (or even an endovascular stenting procedure [5]). The risk of shunt-related complications should decline with newer surgical techniques such as VPS placed under stereotactic guidance and with programmable valves in order to maximize their efficacy and tolerance. However, because the expertise of the surgeon strongly correlated with the surgical outcomes, decisions based on local preferences and expertise need to be followed until a clinical trial demonstrates the superiority of one surgical procedure over the other or allows better characterization of which patients will benefit most from a specific procedure.


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