Update on the application of optic nerve sheath fenestration

Abstract

Background:With the ongoing development of surgical procedures and instruments, the safety of optic nerve sheath fenestration (ONSF) has been improved.

Objective:Through the past three decades, progress has been made in preventing visual loss from chronic optic nerve swelling in idiopathic intracranial hypertension (IIH), secondary intracranial hypertension and local optic nerve diseases. We now review the updated application of ONSF in those diseases.

Methods:The application of ONSF in papilledema due to IIH, secondary intracranial hypertension to cerebral venous sinus occlusion, Cryptococcal meningitis, and intracranial mass or tumors is reviewed. Additionally, the potential benefits of ONSF in local optic neuropathy from optic nerve sheath meningioma, optic nerve drusen, traumatic optic neuropathy and optic nerve/sheath biopsy are also described.

Results:Although ONSF has little or no effect on intracranial pressure, it is a safe, relative easy and effective surgical procedure to prevent or reverse visual loss in IIH. When other treatment modalities fail to timely protect vision, ONSF can be useful in protecting visual function or delay visual loss in secondary intracranial hypertension.

Conclusion:We recommend that ONSF should be considered as a meaningful alternative or an adjunct therapy to reduce or delay the visual morbidity of these diseases, although the use of ONSF for some of them remains controversial.

Keywords

Optic nerve sheath fenestration (ONSF)idiopathic intracranial hypertension (IIH)secondary intracranial hypertension optic neuropathy

1 Introduction

Optic nerve sheath fenestration (ONSF), also known as optic nerve sheath decompression, was first proposed by Wecker in 1872. The procedure involves cutting incisions or windows into the optic nerve sheath to release the cerebral spinal fluid (CSF) from the subarachnoid space of the optic nerve, reducing the pressure surrounding the optic nerve. ONSF was not widely used until 1964, when Smith and Hayreh succeeded in developing animal models of papilledema, thus avoiding the further deterioration of vision. In the 1990s, Sergott published a series of articles and reviews utilizing ONSF, further supporting its effectiveness in relieving papilledema and visual loss (Sergott, 1991a; Sergott et al., 1988; Sergott et al., 1990; Sergott, 1991b). With the development of surgical instruments and procedures (Spiegel et al., 2016), the safety of ONSF has been established with infrequent complications. Most complications are transient and resolve without sequel (Moreau et al., 2014; Banta & Farris, 2000; Obi et al., 2015).

Through the past three decades, more and more ophthalmologists realized that ONSF is an effective surgical treatment to stabilize or improve visual loss in idiopathic intracranial hypertension (IIH) (Banta & Farris, 2000; Agarwal & Yoo, 2007; Ramsey et al., 2006). Additionally, much progress in the use of ONSF has been made on secondary intracranial hypertension due to cerebral venous sinus occlusion (CVST), Cryptococcal meningitis, and intracranial mass or tumors. There have been anecdotal reports of the use of ONSF in local optic neuropathy such as optic nerve sheath meningioma (ONSM), optic nerve drusen, traumatic optic neuropathy (TON) and optic nerve or sheath biopsy. In this paper we review the application of ONSF in IIH, secondary intracranial hypertension and local optic neuropathy.

2 IIH

IIH, typically affecting young obese women of childbearing age, is a syndrome of elevated intracranial pressure in the presence of normal neuroimaging and normal cerebrospinal fluid (CSF) studies. The disease course is generally self-limiting within 6–18 months. However, some patients experience a disabling condition of chronic severe headache and transient obscurations of vision, intracranial noises and diplopia. Severe visual loss occurs in up to 10% of patients (Banta & Farris, 2000).

General recommendations for IIH include evaluation and treatment of potential contributing factors, weight loss, serial lumbar puncture and medical management. After conservative measures are exhausted or intolerable and there is progression of disease, surgery should be considered to avoid further deterioration of visual function (Killer et al., 2009; Acheson, 2006). There are two main surgical procedures: ONSF and shunt procedure. Neither procedure is perfect, either because of their complications, or failure in controlling the symptoms over time, or inability to decrease the intracranial pressure. There are no randomized controlled trials to guide the decision as to which procedure is best (Acheson, 2006). The choice between these two procedures depends on the predominant problem in IIH.

Shunt surgery, usually performed by neurosurgeons, is able to decrease the intracranial pressure and considered to have a better opportunity of relieving headache (Feldon, 2007). However, for traditional CSF diversion procedures, such as LP (lumboperitoneal) shunts and VP (ventriculoperitoneal) shunts, it has been reported that the failure rates of VP shunts are 14%, and LP are 11%; revision rates are higher with LP shunts (60%) than with VP shunts (30%) (Abubaker et al., 2011).

ONSF is an ophthalmological operation. The effects of ONSF on the intracranial pressure are none or modest. It is recommended mainly in those who have limited headache symptoms but significant papilledema or visual impairment and/or in those who have undergone unsuccessful treatment with a shunt or have a contraindication for shunt surgery (Biousse et al., 2012; Acheson, 2006). As early as 1988, Brourman reported and confirmed that ONSF is a preferred surgical procedure to improve and protect visual function in IIH (Banta & Farris, 2000). In 1991, Spoor reported 69 eyes with acute papilledema uniformly had improved visual function after ONSF, and 10 eyes with chronic papilledema had improved visual function after ONSF (Spoor et al., 1991). In 2000, Banta reported an overall 97% rate of visual acuity stabilization or improvement, and an 88% rate of visual field stabilization or improvement following ONSF (Banta & Farris, 2000). Later, multiple cases were studied and concluded that ONSF is safe and effective to manage patients with visual loss and papilledema (Feldon, 2007).

Regarding the appropriate time to perform ONSF, Obi et al recommended that prompt and aggressive performance of ONSF is essential to stop progressive visual decline, and increase the chances for maintaining and preserving of visual function (Obi et al., 2015). More recent studies have suggested that early surgical intervention in those patients with lumbar opening pressures greater than 50 cm may further reduce the risk of permanent visual loss (Robinson et al, 2016).

Additionally, some have found that unilateral ONSF may result in bilateral improvement of papilledema and visual function, suggesting bilateral ONSFs may not always be necessary in patients with bilateral visual loss and papilledema. However, in many cases bilateral surgery may be necessary to completely resolve all papilledema (Sergott et al., 1988; Banta & Farris, 2000).

Although it is debatable which procedure is better, indeed, it is not uncommon that both ONSF and shunt procedures are performed and it is thought that occasionally both procedures may be necessary to control headache as well as arresting visual loss (Sergott et al., 1988; Banta & Farris, 2000). It is mutually complimentary to shunt surgery.

However, after either primary shunt surgery or ONSF surgery, patients with IIH should be closely monitored with both ICP and visual function due to the possibility of failure in controlling symptoms. If symptoms recur or vision deteriorates, repeat ONSF could be performed and improve the patient’s visual function (Spoor et al., 1991; Banta & Farris, 2000). Although repeat ONSF is more complicated than the primary ONSF, it is still safe in general (Spoor et al., 1991; Banta & Farris, 2000).

3 Secondary intracranial hypertension due to CVST, cryptococcal meningitis, intracranial tumors

3.1 CVST

CVST is the obstruction or thrombosis of cerebral venous sinuses producing a clinical syndrome that resembles IIH. Somewhat different from more typical IIH, the increased intracranial pressure (ICP) secondary to CVST can develop fast, with fulminant papilledema and rapid visual loss. Blindness from unremitting papilledema constitutes a major threat to the patient. With the current recommendation of using heparin or low molecular weight heparin in the initial treatment, followed by warfarin, provided there are no other bleeding risks that would make these treatments unsuitable, makes the decision to pursue urgent ONSF challenging (Einhaupl et al., 2006; Sacco et al., 2006). The use of thrombolysis remains controversial and is only recommended in patients who deteriorate despite adequate treatment due to the disease process (Einhaupl et al., 2006). Typical treatment options for raised intracranial pressure include repeated therapeutic lumbar puncture, medication (acetazolamide), CSF shunting or ONSF (Stam, 2005). Obviously, with anticoagulation, hemorrhage is a major concern with repeated lumber punctures or shunting (Sergott, 1991a; Murdock et al., 2014). In these patients, ONSF is a reasonably safe (Moreau et al., 2014) and effective alternative to protect visual function (Sergott, 1991a; Murdock et al., 2014).

In 1991, Sergott first reviewed his preliminary results in five patients with sagittal sinus thrombosis (10 eyes) treated by ONSF. Vision improvement occurred in all 10 eyes (Sergott, 1991b). However, he found that the poorest results for primary ONSF was associated with chronic papilledema secondary to sagittal sinus thrombosis during follow-up. Unfortunately, all ten eyes progressed to no light perception despite bilateral optic nerve sheath decompression and reoperation on two nerves. In 1994, Archeson et al. reported two cases of intracranial hypertension due to dural venous sinus thrombosis treated by ONSF. After surgery the vision in one case maintained stable (6/6) and visual field improved, with unfortunate progression in the other patient (Acheson et al., 1994). In 2005, Gunha et al. reported a patient with chronic papilledema and thrombosis of the superior sagittal, transverse and sigmoid sinuses treated with an optic nerve sheath decompression in the left eye. Although papilledema resolved, severe vision loss remained (Cunha et al., 2005). Sergott noticed that these patients were referred for neuro-ophthalmic evaluation at a much more advanced stage of the disease process (visual acuities were 20/400 or worse) than those with IIH (Sergott, 1991b), which he felt contributed to the poor outcomes. These cases may typify the need for combined ONSF and shunting procedures when vision continues to deteriorate in spite of ONSF.

In 2008, Nithyanandam et al. reported the treatment experience of intracranial hypertension secondary to CVST by ONSF in a tertiary center in India (Nithyanandam et al., 2008). They treated seven patients (14 eyes) with postpartum CVST and nine patients with other causes of CVST (17 eyes). 78% achieved visual improvement and 22% maintained vision in postpartum CVST, while 40% improved and 47% maintained in other causes of CVST three months postoperatively, with 40% improved and 60% maintained in IIH (Nithyanandam et al., 2008). 7 eyes of four patients with CVST and no light perception were treated by ONSF and analyzed separately. Among them 4 eyes showed mild improvement in visual acuity which remained stable during 12 to 24 months follow up (Nithyanandam et al., 2008). They concluded that ONSF was an effective and safe procedure to improve or stabilize vision in patients with visual loss caused by intracranial hypertension from CVST. In 2014, Murdock et al. reported a female patient of CVST with Factor V Leiden mutation, G20210A mutation, Factor XII deficiency, decreased antithrombin III and protein S levels, as well as the use of oral contraceptive pills. She was successfully treated while anti-coagulated by bilateral ONSF without complications. Four months after surgery, the visual acuity improved bilaterally, and papilledema was completely resolved with improved visual fields (Murdock et al., 2014). The author recommended that in selected cases, ONSF was an effective surgical option for the treatment of papilledema due to CVST after medical treatment had failed. In 2014, Moreau et al. published seven cases (14 eyes) of venous sinus thrombosis by ONSF. Although no detailed postoperative visual function changes were described, they concluded that ONSF was safe with minimal complications (Moreau et al., 2014).

Although there are no controlled data, ONSF can help visual function with or without producing or requiring a drop in ICP (Sergott, 1991a; Murdock et al., 2014), The EFNS guideline in 2010 suggested that ONSF should be considered in those patients wherein the vision continues to deteriorate despite repeated lumbar punctures and/or acetazolamide (Einhaupl et al., 2010).

3.2 Cryptococcal meningitis

Cryptococcal meningitis is a global disease with significant morbidity and mortality, in which abnormal ocular findings are seen in about 40% of patients, with papilledema being the most common presenting sign and blurred vision the most common symptom (Lipson et al., 1989; Milman et al., 2008). Even when treated timely with intravenous amphotericin B and oral fluconazole, it has a poor prognosis, where permanent neurologic and ophthalmologic sequelae are common, often with optic atrophy secondary to papilledema. Visual failure is the most important cause of morbidity among those who survive (Milman et al., 2008; Tan, 1988). Vision loss is thought to originate from a combination of chronically elevated intracranial pressure, adhesive arachnoiditis, and/or direct invasion of the visual sensory pathway by the organism (Tan, 1988; Cremer et al., 1997). Apart from medical therapy with antifungal agents, much effort has been made to decrease intracranial pressure and or to protect the optic nerve by repeated lumbar punctures and CSF diverting procedures. Limited success in visual protection has been achieved, with common postoperative complications and relapse (Saeed et al., 2003). In 1987, Tan reported intensive aggressive treatment of papilledema in cryptococcal meningitis by shunting procedures (Tan, 1988). Seven patients showed substantial improvement in vision. He concluded that papilledema and visual failure in cryptococcal meningitis was due to raised intracranial pressure and therefore should be treated vigorously (Tan, 1988).

In 1993, Garrity and associates reported two patients with papilledema and visual loss from cryptococcal meningitis with intracranial hypertension (Garrity et al., 1993). Both patients were treated by ONSF, with cryptococcal organisms present in the dural sheath specimens of both patients despite ongoing antifungal medical therapy. One patient had bilateral non-simultaneous optic nerve sheath fenestrations with visual function improved in one eye. The other patient had bilateral visual improvement after a unilateral optic nerve sheath fenestration. Garrity concluded that when high intracranial pressure appeared to contribute to visual loss, ONSF offered an effective treatment alternative for papilledema and visual loss that occurs with cryptococcal meningitis (Garrity et al., 1993).

Additionally, in 1997, Cremer et al. reported three cases of intracranial hypertension due to cryptococcal meningitis (Cremer et al., 1997). The papilledema in two patients was successfully treated with a combination of ONSF and CSF shunting procedures. The successful treatment of acquired immunodeficiency syndrome (AIDS) complicated with cryptococcal meningitis was reported by Milman et al. (Milman et al., 2008). The patient presented with papilledema and severe progressive visual loss despite medical therapy. Bilateral ONSF resulted in significant improvement in visual acuity and resolution of papilledema.

In Cryptococcal meningitis, the possible spread of the organisms after invasive surgical procedures may occur; this may give pause to pursuing CSF shunting or ONSF in this disease. In fact, for ONSF procedures, postoperative orbital infectious complications have not occurred despite histopathologic evaluation of the optic nerve sheath demonstrating numerous cryptococci (Milman et al., 2008; Cremer et al., 1997; Garrity et al., 1993). Regarding the safety of shunting procedures in cryptococcal meningitis, Tang reported his successful experience of seven CSF shunts inserted even before the starting of antifungal therapy (Tan, 1988). The successful recent applications of shunting procedures in active cryptococcal meningitis seems to support that the active stages of cryptococcal meningitis do not seem to contraindicate the necessity of shunting procedures (Petrou et al., 2012; Liu et al., 2014).

The literature appears to support that ONSF should be considered early in the patients with papilledema who are even in the active stage of Cryptococcal meningitis, in hopes of avoiding further visual function impairment. Moreover, an ONSF might be the preferred initial procedure to CSF shunting for protection of visual function due to common shunt failure, as well as the placing of a foreign body into an infected space (Cremer et al., 1997).

3.3 Intracranial mass or tumors

Intracranial masses or tumors can lead to intracranial hypertension. More often than not, most of the mass or tumor can be removed by neurosurgery. However, some mass lesions can only be partly excised or are non-resectable, thus potentially leading to refractory intracranial hypertension. For those patients, to restore or maintain good visual function for quality of life can be immeasurable. Thus, the consideration of ONSF in these cases may be a reasonable alternative treatment with little complications.

In 1991, Sergott first described the indications for ONSF in patients with chronic papilledema due to non-resectable central nervous system masses such as arteriovenous malformation of the vein of the Galen, meningioma of the falx, and prostate carcinoma metastatic to the region of the superior sagittal sinus (Sergott, 1991a). Although only 2 of 10 patients (4 of 14 eyes) demonstrated visual improvement after ONSF, the other patients stabilized postoperatively. The author noted that the poorest results for primary ONSF were associated with those patients with intracranial mass. However, those patients were all referred in the late stages of their illnesses, thus ensuring a suboptimal outcome (Sergott, 1991b).

In 1992, Horton et al. reported in detail four cases of obstruction of the dural sinuses from intracranial tumors, resembling the presentation of pseudotumor cerebri (Horton et al., 1992). Those lesions described were a presumed meningioma abutting the right transverse sinus which had never been excised, a removed meningioma at the junction of the left transverse and sigmoid sinuses, a removed left acoustic neuroma with occluded left transverse and sigmoid sinuses, and a removed meningioma arising from the falx cerebri that compressed the superior sagittal sinus. After ONSF, both the papilledema and visual function improved rapidly in each patient. The authors concluded that ONSF was an effective operation for the preservation of vision in patients with obstruction of the dural sinuses by meningioma. They recommended that early, aggressive ONSF intervention was essential before chronic atrophic visual pathway changes with incomplete visual restoration occur (Horton et al., 1992).

In 2014, Moreau et al. reported 578 eyes of three hundred thirty-one patients who underwent ONSF for progressive vision loss due to various indications, including cases of frontal astrocytoma (2 eyes), brain stem astrocytoma (2 eyes), glioblastoma multiforme (2 eyes), ependymoma (4 eyes), and meningioma (5 eyes). Although arrest of progression and resolution of papilledema were achieved, no long-term follow-up data were available (Moreau et al., 2014). We have had similar experiences, and therefore agree with Sergott and Horton’s recommendation that ONSF should be considered earlier as an option to prevent or slow the progression visual loss in those patients with chronic increased intracranial pressure due to venous sinus mass compression, or increased intracranial pressure from non-resectable tumors for other palliative reasons (Sergott, 1991a; Horton et al., 1992).

4 Local optic nerve diseases

In addition to the above applications in the secondary intracranial hypertension, in which the optic nerve is compromised by chronic increased intracranial pressure, ONSF has also been performed in some local optic neuropathies such as ONSM, optic nerve drusen, traumatic optic neuropathy as well as several other causes.

4.1 Optic nerve sheath meningioma

ONSM accounts for one-third of primary optic nerve tumors, are the second most common optic nerve tumors after glioma, and are the most common tumors of the optic nerve sheath. The management of ONSM has undergone significant evolution over time. Although radiation therapy has been supported as the primary treatment of choice in ONSM, its management is still somewhat controversial (Turbin et al., 2002). ONSF as an adjuvant therapy to maintain or improve vision in a selected subset of patients may be necessary not only to confirm diagnosis, but reduce transient visual loss in ONSM.

In 2003, Saeed et al. reported ten patients who underwent ONSF for patients with ONSM and impaired vision (Saeed et al., 2003). ONSF was offered by one center (Amsterdam) to patients experiencing progressive visual loss with contraction of visual fields. Eight had an extremely poor visual outcome either immediately or within 2 years of surgery. Only one patient had improved vision that lasted for 10 years, and one retained stable vision (20/50) for 3 years. On the basis of these findings, the authors concluded that they would not recommend optic nerve sheath decompression as a primary treatment to retain vision in ONSMs (Saeed et al., 2003).

Turbin et al. reported in 2006 two patients with unilateral optic nerve sheath meningioma treated with the combination of fractionated stereotactic radiotherapy and ONSF (Turbin et al., 2006). Their first patient had previously undergone fractionated stereotactic radiotherapy. After excision of a dural window and biopsy of the tumor from the nerve sheath, visual acuity improved from 20/200 to 20/25, although immediate postoperative vision fell transiently to no light perception for 12 hours. Seven years later, the visual acuity remained in 20/25 and visual field remained stable with no signs of orbital spread of meningioma at the site of the ONSF (Turbin et al., 2006). The second patient’s visual acuity had fallen to no light perception for two months. He first underwent ONSF and was subsequently treated with fractionated stereotactic radiotherapy. The disc edema improved immediately after ONSF. Light perception returned by the second week after surgery and before the initiation of radiotherapy. By postoperative week 4, the vision had improved to 20/200, with visual field improvement as well. Three and half years later, visual function remained stable with no orbital tumor spread (Turbin et al., 2006). The authors recommended that in patients with optic nerve sheath meningioma presenting with severe disc edema and rapid vision loss, ONSF should be considered as an adjuvant vision-preserving therapy either before or after the radiation therapy (Turbinet al., 2006).

VanderVeen et al. in 2009 reported a case of a child with neurofibromatosis type 1 and an isolated optic nerve glioma in which the orbital MRI showed a large intraorbital optic nerve glioma with kinking and fluid within the sheath (Vanderveen et al., 2009). After ONSF, the relative afferent pupillary defect, disk edema, and visual field improved over two years’ follow up. The authors concluded that ONSF may not be helpful in all the cases of optic nerve glioma, but should be considered in those cases of documented progression visual loss and demonstration of fluid entrapment within the optic sheath on MRI (Vanderveen et al., 2009).

Kitzmann et al. in 2008 reported an unusual case of bilateral optic nerve infiltration secondary to peripheral T-cell Non-Hodgkins Lymphoma with CNS involvement and decreased vision due to lymphomatous infiltration of the optic nerves (Kitzmann et al., 2008). Although significant bilateral visual function improvement was noted post-operatively from unilateral surgery, the operated eye ultimately lost vision to further infiltration.

Gasperini et al. in 2007 reported a case of bilateral anterior optic neuropathy in a patient with metastatic breast cancer treated by optic nerve sheath fenestration (Gasperini et al., 2007). The patient was diagnosed with central nervous system metastasis from breast carcinoma, confirmed by cerebrospinal fluid (CSF) cytology. MRI of the brain and orbits revealed diffuse enhancement of the meninges and perineural (intrasheath) enhancement of both optic nerves. No opening pressure was obtained. ONSF was performed on the left eye with significant improvement in visual function bilaterally. One month after ONSF, the visual acuity and color vision modestly improved, as well as the bilateral optic disc swelling. At one year there was no evidence of optic nerve swelling. The authors recommended that ONSF should be considered as a treatment option for optic neuropathy caused by perineural or intrasheath metastasis, especially in cases where alternative treatments are not tolerated and visual loss is severe at presentation (Gasperini et al., 2007).

4.2 Optic nerve drusen

Optic nerve drusen are globular, often calcified, hyaline bodies located within the optic nerve head. Optic nerve drusen usually do not affect vision. However, peripheral visual field loss may occur slowly, and the amount of visual field loss varies from none to severe constriction of the peripheral visual field. There is no proven or standard treatment for progressive visual loss secondary to optic nervedrusen.

In 1991, Sergott first listed his preliminary results about optic nerve drusen treated by ONSF. He treated four cases of optic nerve drusen with ONSF and visual improvement occurred in two cases (Sergott, 1991b). Several other reports of optic nerve drusen treated with ONSF have been reported with similar results (Jiraskova & Rozsival, 1999; Jiraskova & Rozsival, 1996). Recently Moreau et al. published in detail their results with patients suffering progressive visual loss due to optic nerve drusen treated by ONSF. A total of 13 eyes (eleven patients) with disc swelling, progressive visual field loss and central visual acuity loss were treated. Although the sample size was small, ONSF showed stabilization or improvement of visual acuity in all 12 eyes (postoperative visual acuity data were only available for 12 eyes) with visual field stabilization or improvement in 8 of 9 eyes. The exact mechanism as to why patients with optic nerve drusen and progressive visual loss benefit from ONSF is unclear. The authors suggest that ONSF may be beneficial in halting progressive visual loss due to optic nerve drusen (Moreau et al., 2014).

4.3 Traumatic optic neuropathy

TON often causes severe loss of vision due to direct trauma, indirect trauma, or a combination of both (Samardzic et al., 2012). The mechanism of indirect TON is diverse and complicated. There is no consensus as to the optimum treatment for TON (Volpe and Levin, 2011). The largest prospective comparison study of patients of all ages with TON found no difference in outcome among patients treated with surgical optic nerve canal decompression, high dose steroids, or observation (Levin et al., 1999). A recent study has suggested that the decision to intervene in TON medically, surgically, or simply observe be on an individual basis, rather than a structured standard of care (Zhilin et al., 2011).

Some studies, although anecdotal, indicated some subtypes of post-traumatic optic neuropathy could benefit from ONSF. In 1984, Hupp et al. first reported post-traumatic venous obstructive retinopathy associated with enlarged optic nerve sheath and progressive visual loss improving after ONSF (Hupp et al., 1984). Additionally, Wojno et al. reported a patient with TON who benefit from ONSF and suggested that ONSF should be considered when there is no spontaneous improvement of vision or severe headache in traumatic optic neuropathy (Wojno et al., 1986). On rare occasions, optic nerve sheath hematoma may result from TON, although difficult to demonstrate radiographically. For these and other reasons, there are only a few reported cases of fenestration of the enlarged optic nerve sheath from TON. In 1989, Guy et al. reported the first clinically confirmed case of hemorrhage into the optic nerve sheath with ONSF through a medial approach (Guy et al., 1989). In another study, Mauriello et al. found seven of nine patients with an enlarged optic nerve sheath after TON showed improvement after ONSF. They suggested that an enlarged optic nerve sheath was associated with an improved prognosis (Mauriello et al., 1992). Muthukumar et al. later reported a case of visual loss following hemorrhage into the optic nerve sheath following head trauma. The patient showed improvement in visual function following a small clot evacuated by ONSF (Muthukumar, 1997). They suggested that treatment of traumatic optic nerve sheath hematoma by ONSF should be considered in selected patients, while agreeing that the management of traumatic optic neuropathy is controversial (Hupp et al., 1984; Sergott et al., 1990; Mauriello et al., 1992; Muthukumar, 1997; Goldenberg-Cohen et al., 2004; Guy et al., 1989).

In 2014, Hui et al. successfully treated two cases of presumed optic nerve sheath hematoma from TON with ONSF. The patients were ultimately diagnosed as an optic nerve sheath meningocele, in which the patients received immediate orbit/head pain resolution with significant visual improvement within a week after ONSF (Hui et al., 2014). The literature seems to suggest that ONSF should be considered in TON when the patient’s visual function is progressively worsening due to presumed subdural hematoma, or when the optic nerve sheath remains distended and/or papilledema persists in TON. Neuro-imaging may or may not be helpful in these cases, and therefore need to be assessed on an individual basis. Combined optic canal decompression with ONSF may be additionally helpful (Yu-Wai-Man and Griffiths, 2005; Li et al.,1997).

5 Optic nerve or nerve sheath biopsy

The optic nerve or sheath can be involved with tumor, infection, infiltration or inflammation. The treatments for these disorders are obviously quite different. The diagnosis is often based on typical clinical findings and radiological features. However, sometimes the diagnosis can be extremely difficult on the basis of clinical and imaging features, with significant overlap of diagnostic possibilities. Optic nerve lymphoma (Vaphiades et al., 2016), haemangiopericytoma (Schwent et al., 2007), schwannoma, sarcoidosis, tuberculosis, and aspergillosis all may mimic primary optic nerve or optic nerve sheath tumors. CSF analysis can be helpful to make the diagnosis, but often requires multiple samples with a low yield. An accurate diagnosis may require a biopsy of the optic nerve or sheath particularly when the clinical behavior and radiological findings are atypical (Khong & McNab, 2012). The optic nerve or sheath biopsy can be achieved by a medial transconjunctival orbitotomy, a lateral orbitotomy, or transcranial approach. The surgical biopsy procedures via the medial transconjunctival orbitotomy approach are similar to ONSF (Gunduz et al., 2010). Although the medial transconjunctival ONSF method may limit biopsy size, its relative safety of surgical procedure and ease of obtaining tissue biopsy makes the procedure worth considering in particularly difficult cases.

Dayan et al. in 2000 reported bilateral lymphomatous optic neuropathy diagnosed by optic nerve biopsy through a medial transconjunctival approach (Dayan et al., 2000). Although the optic nerve sheath biopsied was not diagnostic, the material from the biopsied optic nerve showed infiltration by a low grade B cell non-Hodgkin’s lymphoma. The visual acuity deteriorated immediately postoperatively, but the visual function improved to the prebiopsy level several months after following low dose radiotherapy. The author suggested that diagnostic optic nerve biopsy might be considered for diagnosis in enigmatic cases even when visual function remained (Dayan et al., 2000).

In 2010, Gunduz et al. evaluated the role of optic nerve biopsy in the diagnosis and management of optic nerve and sheath tumors. Their study described in detail the surgical procedures of the optic nerve biopsy via a medial transconjunctival orbitotomy approach, similar to optic nerve sheath decompression used in patients with pseudotumor cerebri. Seven patients with progressive optic nerve and sheath tumors were included. No complications related to the surgical procedure were noted. Histopathological examination revealed that five patients had juvenile pilocytic astrocytoma and two patients had optic nerve sheath meningioma. They concluded that optic nerve biopsy by the medial transconjunctival approach was relatively safe and it could be used to obtain histopathologic proof in selected cases of progressive optic nerve tumors for which treatment is deemed necessary, although the sample size was relatively small (Gunduz et al., 2010).

Khong et al. in 2012 described another four cases of progressive optic neuropathy with uncertain diagnosis after negative systemic investigations, which were biopsied by a medial transconjucntival approach as well. In all four cases, no complications were noted; specifically there was no reported deterioration in vision. Although one case of neurosarcoidosis was confirmed by the biopsy, the other three cases were non-diagnostic. The authors felt that the procedure, although non-diagnostic in three cases, was still helpful in ruling out serious causes such as central nervous system leukemia relapse. They concluded that the medial transconjunctival approach to optic nerve biopsy was a minimally invasive and safe technique (Khong & McNab, 2012).

Recently, Sobel et al. in 2015 investigated the diagnostic value of optic nerve sheath biopsy during ONSF in idiopathic intracranial hypertension (Sobel et al., 2015). Although they suggested that in patients with classic signs of idiopathic intracranial hypertension a pathologic study of window sheath tissue was not necessary, they also demonstrated that in patients whom the diagnosis is unclear, the specimen should be sent for pathologic diagnosis. Six patients returned with unexpected biopsy results, including diagnoses of meningioma, lymphoma, metastatic breast cancer, metastatic carcinoma, and fungal optic neuritis (Sobel et al., 2015).

6 Other rare diseases

ONSF has also been used in some rare diseases such as osteopetrosis (Allen et al., 2006), craniometaphyseal dysplasia (Singhal & Cochrane, 2008) and radiation-induced optic neuropathy (Mohamed et al., 2000).

Osteopetrosis, literally “stone bone”, also known as Albers-Schönberg disease, is an extremely rare inherited disorder whereby bones progressively harden. Cranial nerve dysfunction often occurs as the result of stenosis of foramina at the skull base. The cause of visual loss in osteopetrosis may be due to a compressive optic neuropathy from narrowing at the optic canal or may be due to increased intracranial pressure (for example, cerebral venous outflow obstruction or restriction at the foramen magnum) (Hoyt & Billson, 1979). Although some success in the treatment of infantile osteopetrosis with a total bone marrow transplant has been reported (Kerr et al., 2000; Tolar et al., 2004), there are few effective reported treatment options for the visual loss. In 2006, Richard described a patient with visual loss from osteopetrosis-related optic nerve edema that improved after ONSF (Allen et al., 2006). The patient was noted to have bilateral progressive visual loss with optic nerve edema. A unilateral ONSF was performed. Two months after ONSF, there was noted improvement of visual function and optic nerve edema. Although a lumbar puncture demonstrated a normal opening pressure, the authors felt that the visual loss in this patient with optic nerve edema was due to increased intracranial pressure (Allen et al., 2006).

Craniometaphyseal dysplasia is a rare genetic disorder of the skull bones characterized by a childhood presentation with endochondral and intramembranous ossification (Greenspan, 1991). Clinical features include cranial nerve entrapment, facial abnormalities, cranial neuropathies, and raised intracranial pressure (Beighton, 1995). The treatment for this disorder is difficult and mainly the craniofacial surgery such as bilateral fronto-parieto-temporal expansile cranioplasty. However, bone regrowth is common.

Early surgical treatment to relieve cranial pressure may help eliminate the sight and hearing complications associated with this disorder. Ash and David described their experience of management of craniometaphyseal dysplasia with bilateral fronto-parieto-temporal expansile cranioplasty and right optic nerve sheath fenestration (Singhal & Cochrane, 2008). The patient presented with seizures, headaches, and diminished visual acuity, and was found to have chronic bilateral papilledema. Lumbar puncture demonstrated raised opening pressure (50 cm of water). Six months after the surgery the patient’s headaches and papilledema completely resolved. The visual acuity improved as did the seizure control. The authors concluded that expansile cranioplasty, in conjunction with ONSF, may represent a safe and effective treatment for raised ICP associated with craniometaphyseal dysplasia (Singhal & Cochrane, 2008).

Radiation-induced optic neuropathy (RION) is a devastating complication of radiotherapy to the anterior visual pathway resulting in painless, progressive, monocular or binocular loss of vision months to years after radiotherapy. Treatment with systemic corticosteroids, anticoagulation and hyperbaric oxygen remains controversial (Danesh-Meyer, 2008). In 2000, Mohamed reported three consecutive patients with radiation-induced optic neuropathy treated successfully by ONSF (Mohamed et al., 2000). The authors believed that every effort should be made to distinguish and preserve vision among patients with developing RION. The authors suggest that ONSF should be considered an early surgical approach that has potential in helping those patients with RION as radiation induces edema and causes increased perineural pressure in an optic nerve because of the sheath confinement (Mohamed et al., 2000).

Although the above articles demonstrate ONSF could be a potential good adjunct treatment to protect or restore the visual function, the treatment approach in optic neuropathy due to RION remains controversial and needs further study.

7 Summary

With the development of surgical approaches and instruments for ONSF, the complications of ONSF have been increasingly reduced and its safety has been well established (Obi et al., 2015; Banta & Farris, 2000; Moreau et al., 2014).

Similar to IIH, one of the most important goals of treatment for secondary intracranial hypertension from CVST, Cryptococcus meningitis and intracranial tumors is to prevent or halt progressive visual loss associated with intracranial hypertension. Although few evidence-based articles have been published due to the relative small cases and lack of control data, the above reviewed literature seems to indicate that ONSF can be used to prevent or reverse vision loss in secondary intracranial hypertension, particularly when other treatment modalities fail to protectvision.

Additionally, the possibility of optic nerve sheath and/or nerve biopsy in more difficult diagnostic cases associated with visual loss should be considered. Although there are several surgical approaches for ONSF, the medial transconjunctival approach (with or without medial rectus removal) is relatively easy and low-risk for experienced surgeons.

Footnotes

Acknowledgments

The present work was jointly funded by the National Basic Research Program of China (973 Program) (No. 2015CB554100), National Natural Science Foundation of China (No. 81271035/H1205), High and New Technology Program in Sichuan Academy of Medical Sciences & Sichuan Provincial People’s Hospital of China (No. 2012-6), and 2015 Foundation for Returned Personals Studying Abroad in Human Resources Department of Sichuan Province, China.

References

Abubaker

, Ali

, Raza

, Bolger

, Rawluk

, & O’Brien

(2011). Idiopathic intracranial hypertension: Lumboperitoneal shunts versus ventriculoperitoneal shunts–case series and literature review. British Journal of Neurosurgery, 25(1), 94–99.

Acheson

J.F.

(2006). Idiopathic intracranial hypertension and visual function. British Medical Bulletin, 79-80(1), 233–244.

Acheson

J.F.

, Green

W.T.

, & Sanders

M.D.

(1994). Optic nerve sheath decompression for the treatment of visual failure in chronic raised intracranial pressure. Journal of Neurology, Neurosurgery & Psychiatry, 57(11), 1426–1429.

Agarwal

M.R.

, & Yoo

J.H.

(2007). Optic nerve sheath fenestration for vision preservation in idiopathic intracranial hypertension. Neurosurgical Focus, 23(5), E7.

Allen

R.C.

, Nerad

J.A.

, Kattah

J.C.

, & Lee

A.G.

(2006). Resolution of optic nerve edema and improved visual function after optic nerve sheath fenestration in a patient with osteopetrosis. American Journal of Ophthalmology, 141(5), 945–947.

Banta

J.T.

, & Farris

B.K.

(2000). Pseudotumor cerebri and optic nerve sheath decompression. Ophthalmology, 107(10), 1907–1912.

Beighton

(1995). Craniometaphyseal dysplasia (CMD), autosomal dominant form. Journal of Medical Genetics, 32(5), 370–374.

Biousse

, Bruce

B.B.

, & Newman

N.J.

(2012). Update on the pathophysiology and management of idiopathic intracranial hypertension. Journal of Neurology, Neurosurgery & Psychiatry, 83(5), 488–494.

Cremer

P.D.

, Johnston

I.H.

, & Halmagyi

G.M.

(1997). Pseudotumour cerebri syndrome due to cryptococcal meningitis. Journal of Neurology, Neurosurgery & Psychiatry, 62(1), 96–98.

10.

Cunha

L.P.

, Goncalves

A.C.

, Moura

F.C.

, & Monteiro

M.L.

(2005). Severe bilateral visual loss as the presenting sign of cerebral venous sinus thrombosis: Case report. Arquivos Brasileiros de Oftalmologia, 68(4), 533–537.

11.

Danesh-Meyer

H.V.

(2008). Radiation-induced optic neuropathy. Journal of Clinical Neuroscience, 15(2), 95–100.

12.

Dayan

M.R.

, Elston

J.S.

, & McDonald

(2000). Bilateral lymphomatous optic neuropathy diagnosed on optic nerve biopsy. Archives of Ophthalmology, 118(10), 1455–1457.

13.

Einhaupl

, Bousser

M.G.

, de Bruijn

S.F.

, Ferro

J.M.

, Martinelli

, Masuhr

, & Stam

(2006). EFNS guideline on the treatment of cerebral venous and sinus thrombosis. European Journal of Neurology, 13(6), 553–559.

14.

Einhaupl

, Stam

, Bousser

M.G.

, De Bruijn

S.F.

, Ferro

J.M.

, Martinelli

, & Masuhr

(2010). EFNS guideline on the treatment of cerebral venous and sinus thrombosis in adult patients. European Journal of Neurology, 17(10), 1229–1235.

15.

Feldon

S.E.

(2007). Visual outcomes comparing surgical techniques for management of severe idiopathic intracranial hypertension. Neurosurgical Focus, 23(5), E6.

16.

Garrity

J.A.

, Herman

D.C.

, Imes

, Fries

, Hughes

C.F.

, & Campbell

R.J.

(1993). Optic nerve sheath decompression for visual loss in patients with acquired immunodeficiency syndrome and cryptococcal meningitis with papilledema. American Journal of Ophthalmology, 116(4), 472–478.

17.

Gasperini

, Black

, & Van Stavern

(2007). Perineural metastasis of breast cancer treated with optic nerve sheath fenestration. Ophthalmic Plastic & Reconstructive Surgery, 23(4), 331–333.

18.

Goldenberg-Cohen

, Miller

N.R.

, & Repka

M.X.

(2004). Traumatic optic neuropathy in children and adolescents. Journal of AAPOS, 8(1), 20–27.

19.

Greenspan

(1991). Sclerosing bone dysplasias–a target-site approach. Skeletal Radiology, 20(8), 561–583.

20.

Gunduz

, Catak

, & Erden

(2010). Optic nerve biopsy via a medial transconjunctival orbitotomy approach in the diagnosis of optic nerve and sheath tumors. Orbit, 29(4), 190–193.

21.

Guy

, Sherwood

, & Day

A.L.

(1989). Surgical treatment of progressive visual loss in traumatic optic neuropathy. Report of two cases. Journal of Neurosurgery, 70(5), 799–801.

22.

Horton

J.C.

, Seiff

S.R.

, Pitts

L.H.

, Weinstein

P.R.

, Rosenblum

M.L.

, & Hoyt

W.F.

(1992). Decompression of the optic nerve sheath for vision-threatening papilledema caused by dural sinus occlusion. Neurosurgery, 31(2), 203–211, 211-212.

23.

Hoyt

C.S.

, & Billson

F.A.

(1979). Visual loss in osteopetrosis. The American Journal Of Diseases Of Children, 133(9), 955–958.

24.

Hui

, Xiaoyun

, Yi

, Ningbo

, Xizhong

, Shaowei

, Wei

, Maozhu

, Wubo

, Xuefei

, Li

, Haibin

, Daiwen

, & Yong

(2014). Visual improvement and pain resolution in traumatic optic nerve sheath meningocele treated by optic nerve sheath fenestration. Restorative Neurology and Neuroscience, 32(5), 655–661.

25.

Hupp

S.L.

, Buckley

E.G.

, Byrne

S.F.

, Tenzel

R.R.

, Glaser

J.S.

, & Schatz

N.S.

(1984). Posttraumatic venous obstructive retinopathy associated with enlarged optic nerve sheath. Archives of Ophthalmology, 102(2), 254–256.

26.

Jiraskova

, & Rozsival

(1996). Decompression of the optic nerve sheath–results in the first 37 operated eyes. Ceska a Slovenska Oftalmologie, 52(5), 297–307.

27.

Jiraskova

, & Rozsival

(1999). Results of 62 optic nerve sheath decompressions. Ceska a Slovenska Oftalmologie, 55(3), 136–144.

28.

Kerr

N.C.

, Wang

W.C.

, Mohadjer

, Haik

B.G.

, Kaste

S.C.

, & Horwitz

E.M.

(2000). Reversal of optic canal stenosis in osteopetrosis after bone marrow transplant. American Journal of Ophthalmology, 130(3), 370–372.

29.

Khong

J.J.

, & McNab

A.A.

(2012). Medial transconjunctival intrinsic optic nerve biopsy: Surgical technique and indications. Orbit, 31(4), 227–232.

30.

Killer

H.E.

, Jaggi

G.P.

, & Miller

N.R.

(2009). Papilledema revisited: Is its pathophysiology really understood? Clinical & Experimental Ophthalmology, 37(5), 444–447.

31.

Kitzmann

A.S.

, Pulido

J.S.

, Garrity

J.A.

, & Witzig

T.E.

(2008). Histologic findings in T-cell lymphoma infiltration of the optic nerve. Ophthalmology, 115(5), e1–e6.

32.

Levin

L.A.

, Beck

R.W.

, Joseph

M.P.

, Seiff

, & Kraker

(1999). The treatment of traumatic optic neuropathy: The International Optic Nerve Trauma Study. Ophthalmology, 106(7), 1268–1277.

33.

K.K.

, Meara

J.G.

, & Joseph

M.P.

(1997). Reversal of blindness after facial fracture repair by prompt optic nerve decompression. Journal of Oral and Maxillofacial Surgery, 55(6), 648–650.

34.

Lipson

B.K.

, Freeman

W.R.

, Beniz

, Goldbaum

M.H.

, Hesselink

J.R.

, Weinreb

R.N.

, & Sadun

A.A.

(1989). Optic neuropathy associated with cryptococcal arachnoiditis in AIDS patients. American Journal of Ophthalmology, 107(5), 523–527.

35.

Liu

, Zhang

, Tang

, & Lu

(2014). The use of ventriculoperitoneal shunts for uncontrollable intracranial hypertension in patients with HIV-associated cryptococcal meningitis with or without hydrocephalus. BioScience Trends, 8(6), 327–332.

36.

Mauriello

J.A.

, DeLuca

, Krieger

, Schulder

, & Frohman

(1992). Management of traumatic optic neuropathy–a study of 23 patients. British Journal of Ophthalmology, 76(6), 349–352.

37.

Milman

, Mirani

, & Turbin

R.E.

(2008). Optic nerve sheath fenestration in cryptococcal meningitis. Clinical Ophthalmology, 2(3), 637–639.

38.

Mohamed

I.G.

, Roa

, Fulton

, Halls

, Jha

, Kherani

, & Johnson

(2000). Optic nerve sheath fenestration for a reversible optic neuropathy in radiation oncology. American Journal of Clinical Oncology, 23(4), 401–405.

39.

Moreau

, Lao

K.C.

, & Farris

B.K.

(2014). Optic nerve sheath decompression: A surgical technique with minimal operative complications. Journal of Neuro-Ophthalmology, 34(1), 34–38.

40.

Murdock

, Tzu

J.H.

, Schatz

N.J.

, & Lee

W.W.

(2014). Optic nerve sheath fenestration for the treatment of papilledema secondary to cerebral venous thrombosis. Journal of Neuro-Ophthalmology, 34(1), 67–69.

41.

Muthukumar

(1997). Traumatic haemorrhagic optic neuropathy: Case report. British Journal of Neurosurgery, 11(2), 166–167.

42.

Nithyanandam

, Manayath

G.J.

, & Battu

R.R.

(2008). Optic nerve sheath decompression for visual loss in intracranial hypertension: Report from a tertiary care center in South India. Indian Journal of Ophthalmology, 56(2), 115–120.

43.

Obi

E.E.

, Lakhani

B.K.

, Burns

, & Sampath

(2015). Optic nerve sheath fenestration for idiopathic intracranial hypertension: A seven year review of visual outcomes in a tertiary centre. Clinical Neurology and Neurosurgery, 137, 94–101.

44.

Petrou

, Moscovici

, Leker

R.R.

, Itshayek

, Gomori

J.M.

, & Cohen

J.E.

(2012). Ventriculoperitoneal shunt for intracranial hypertension in cryptococcal meningitis without hydrocephalus. Journal of Clinical Neuroscience, 19(8), 1175–1176.

45.

Ramsey

C.R.

, Proctor

B.L.

, Baker

R.S.

, & Pittman

(2006). Prevention of visual loss caused by shunt failure: A potential role for optic nerve sheath fenestration. Report of three cases. Journal of Neurosurgery, 104(2 Suppl), 149–151.

46.

Robinson

M.E.

, Moreau

, OMeilia

, Pagteilan

, Ding

, Siatkowski

R.M.

, & Farris

B.K.

(2016). The relationship between optic nerve sheath decompression failure and intracranial pressure in idiopathic intracranial hypertension. Journal of Neuro-Ophthalmology, 36(3), 246–251.

47.

Sacco

R.L.

, Adams

, Albers

, Alberts

M.J.

, Benavente

, Furie

, Goldstein

L.B.

, Gorelick

, Halperin

, Harbaugh

, Johnston

S.C.

, Katzan

, Kelly-Hayes

, Kenton

E.J.

, Marks

, Schwamm

L.H.

, & Tomsick

(2006). Guidelines for prevention of stroke in patients with ischemic stroke or transient ischemic attack: A statement for healthcare professionals from the American Heart Association/American Stroke Association Council on Stroke: Co-sponsored by the Council on Cardiovascular Radiology and Intervention: The American Academy of Neurology affirms the value of this guideline. Circulation, 113(10), e409–e449.

48.

Saeed

, Rootman

, Nugent

R.A.

, White

V.A.

, Mackenzie

I.R.

, & Koornneef

(2003). Optic nerve sheath meningiomas. Ophthalmology, 110(10), 2019–2030.

49.

Samardzic

, Samardzic

, Janjetovic

, Samardzic

, Sekelj

, & Latic-Hodzic

(2012). Traumatic optic neuropathy - to treat or to observe? Acta Informatica Medica, 20(2), 131–132.

50.

Schwent

B.J.

, Wojno

T.H.

, & Grossniklaus

H.E.

(2007). Hemangiopericytoma of the optic nerve sheath. American Journal of Ophthalmology, 143(5), 904–906.

51.

Sergott

R.C.

(1991a). Optic nerve sheath decompression: History, techniques, and indications. International Ophthalmology Clinics, 31(4), 71–81.

52.

Sergott

R.C.

(1991b) Optic nerve sheath decompression: Neuropathologic, clinical, and hemodynamic results and rationale. Transactions of the American Ophthalmological Society, 89, 675–720.

53.

Sergott

R.C.

, Savino

P.J.

, & Bosley

T.M.

(1988). Modified optic nerve sheath decompression provides long-term visual improvement for pseudotumor cerebri. Archives of Ophthalmology, 106(10), 1384–1390.

54.

Sergott

R.C.

, Savino

P.J.

, & Bosley

T.M.

(1990). Optic nerve sheath decompression: A clinical review and proposed pathophysiologic mechanism. Australian and New Zealand Journal of Ophthalmology, 18(4), 365–373.

55.

Singhal

, & Cochrane

D.D.

(2008). Optic nerve sheath fenestration and bilateral expansile cranioplasty for raised intracranial pressure in craniometaphyseal dysplasia: A case report. Child’s Nervous System, 24(4), 521–524.

56.

Sobel

R.K.

, Syed

N.A.

, Carter

K.D.

, & Allen

R.C.

(2015). Optic nerve sheath fenestration: current preferences in surgical approach and biopsy. Ophthalmic Plastic & Reconstructive Surgery, 31(4), 310–312.

57.

Spiegel

J.A.

, Sokol

J.A.

, Whittaker

T.J.

, Bernard

, & Farris

B.K.

(2016). Farris-Tang retractor in optic nerve sheath decompression surgery. Orbit, 35(1), 39–41.

58.

Spoor

T.C.

, Ramocki

J.M.

, Madion

M.P.

, & Wilkinson

M.J.

(1991). Treatment of pseudotumor cerebri by primary and secondary optic nerve sheath decompression. American Journal of Ophthalmology, 112(2), 177–185.

59.

Stam

(2005). Thrombosis of the cerebral veins and sinuses. The New England Journal of Medicine, 352(17), 1791–1798.

60.

Tan

C.T.

(1988). Intracranial hypertension causing visual failure in cryptococcus meningitis. Journal of Neurology, Neurosurgery & Psychiatry, 51(7), 944–946.

61.

Tolar

, Teitelbaum

S.L.

, & Orchard

P.J.

(2004). Osteopetrosis. The New England Journal of Medicine, 351(27), 2839–2849.

62.

Turbin

R.E.

, Thompson

C.R.

, Kennerdell

J.S.

, Cockerham

K.P.

, & Kupersmith

M.J.

(2002). A long-term visual outcome comparison in patients with optic nerve sheath meningioma managed with observation, surgery, radiotherapy, or surgery and radiotherapy. Ophthalmology, 109(5), 890–899, 899-900.

63.

Turbin

R.E.

, Wladis

E.J.

, Frohman

L.P.

, Langer

P.D.

, & Kennerdell

J.S.

(2006). Role for surgery as adjuvant therapy in optic nerve sheath meningioma. Ophthalmic Plastic & Reconstructive Surgery, 22(4), 278–282.

64.

Vanderveen

D.K.

, Nihalani

B.R.

, Barron

, & Anderson

R.L.

(2009). Optic nerve sheath fenestration for an isolated optic nerve glioma. Journal of AAPOS, 13(1), 88–90.

65.

Vaphiades

M.S.

, Nagia

, Keeble

E.B.

, & Roberson

G.H.

(2016). Optic Neuropathy due to chronic lymphocytic leukemia proven with optic nerve sheath biopsy and chronic myelogenous leukemia relapse presenting with central nervous system blast crisis and bilateral optic nerve infiltration: Comment. Journal of Neuro-Ophthalmology, 36(2), 223–224.

66.

Volpe

N.J.

, & Levin

L.A.

(2011). How should patients with indirect traumatic optic neuropathy be treated? Journal of Neuro-Ophthalmology, 31(2), 169–174.

67.

Wojno

, Beck

R.W.

, & Grosserode

(1986). Bilateral optic nerve sheath enlargement. Ophthalmic Surgery, 17(9), 584–588.

68.

Yu-Wai-Man

, & Griffiths

P.G.

(2005). Surgery for traumatic optic neuropathy. Cochrane Database of Systematic Reviews, 19(4), D5024.

69.

Zhilin

, Huoniu

, Zhihua

, & Guorong

(2011). Wide optic nerve canal decompression for the treatment of blindness resulting from an indirect optic nerve injury. Journal of Craniofacial Surgery, 22(4), 1463–1465.