Complications of Optic Nerve Sheath Fenestration as a Treatment for Idiopathic Intracranial Hypertension

The Pseudotumor Cerebri Syndrome

Pseudotumor cerebri syndrome is a syndrome of increased cerebrospinal fluid pressure without ventriculomegaly, mass lesion, or meningeal abnormality. It is either primary (idiopathic intracranial hypertension, IIH) or secondary. A secondary cause is unlikely when adhering to the diagnostic criteria. Permanent visual loss occurs if undetected or untreated, and the associated headaches may be debilitating. Fulminant disease may result in blindness despite aggressive treatment. This study addresses the diagnosis and management of IIH including new insights into the pathobiology of IIH, updates in therapeutics and causes of overdiagnosis.

Cranial decompression and expansion surgery for the treatment of refractory idiopathic intracranial hypertension: case report and systematic review

OBJECTIVE

The purpose of this study is to systematically review the literature on the clinical outcomes following different surgical techniques in patients with refractory idiopathic intracranial hypertension (IIH).

BACKGROUND

IIH is a condition characterised by increased cranial pressure (ICP) in the absence of an intracranial lesion that does not adequately respond to different medical and surgical therapies. Cranial decompression or expansion surgeries are a last resort therapy for patients with refractory IIH.

METHODS

A systematic literature search of the databases of PubMed, Embase and Medline from inception to 2019 was performed. Searches were limited to the English language and to clinical studies. Studies were included if clinical outcomes following different cranial decompression or expansion techniques were reported. We also add one case of our own experience with performing a bilateral frontoparietal expansion craniotomy and subtemporal craniectomy.

RESULTS

Five manuscripts, describing 38 procedures, met the inclusion criteria. Thirty-one patients were female (82%). The mean age was 26.2 years. The techniques studied included subtemporal craniectomy (27/38, 71%), internal cranial expansion (10/38, 26%), and cranial morcellation decompression (1/38, 3%). Thirty-five patients presented with headaches of which 17 noted postoperative improvement or resolution (49%). Visual deficits were documented in 30 patients and 25 reported postoperative improvement (83%). Papilledema disappeared in 23 of 32 patients with this sign at presentation (72%). In our patient, symptoms completely resolved postoperatively and a 6% increase in intracranial volume was measured.

CONCLUSIONS

Cranial vault decompression or expansion surgeries may be an effective last resort therapy for patients with refractory IIH. These surgeries expand the intracranial volume, and thus may normalise ICP, leading to clinical improvement.

Intracranial venous stenting for idiopathic intracranial hypertension

INTRODUCTION

There is increasing evidence in the literature to support venous sinus stenting in patients with idiopathic intracranial hypertension who fail first-line therapy. Venous sinus stenting is a safe and successful technique compared with cerebrospinal fluid diversion procedures. This study examines the clinical outcomes of patients post intracranial venous stenting for intracranial hypertension across three tertiary hospitals in Western Australia.

METHODS

A retrospective analysis was performed on 83 consecutive patients treated with intracranial venous stenting for IIH at three tertiary hospitals from October 2013 to March 2020. Data were collected from outpatient clinic letters, electronic discharge letters, electronic radiological imaging and procedural reports.

RESULTS

89.2% patients were able to cease Acetazolomide post stenting. 78.3% patients reported resolution of headaches. 84.3% patients demonstrated resolution of their papilloedema. 91.6% patients demonstrated improvement of their visual acuity. Compared with a recent meta-analysis by Satti and Chaudry in 2015, our results demonstrated a higher technical success rate and lower complication rates.

CONCLUSION

Our study findings support the paradigm shift from CSF diversion procedures to venous sinus stenting in patients with IIH who fail first-line therapy. Venous sinus stenting has a high technical success rate and significantly lower complication rates than other invasive treatments.

Optic nerve sheath fenestration for treating papilloedema in the era of cerebral venous sinus stenting

BACKGROUND

Pseudotumour cerebri (PTC) is the syndrome of intracranial hypertension without intracranial mass or hydrocephalus and is the commonest cause of papilloedema seen in many eye clinics. In the last 10 years, we have increasingly used TSS in patients whose papilloedema was not well controlled with medical treatment and have done fewer ONSFs. Here, we review our experience at Royal Prince Alfred Hospital Sydney with ONSF in 35 patients over the period 2002-2021.

METHODS

Retrospective case series of 35 patients, 30 of whom had primary PTC [i.e., idiopathic intracranial hypertension (IIH)] and 5 with secondary PTC.

RESULTS

Eighteen patients had bilateral ONSF and 17 patients unilateral ONSF, in each case of the worse eye. Thirteen patients then underwent transverse sinus stenting (TSS), in each case following ONSF. The primary outcome measures were visual acuity (VA) and mean deviation (MD) on visual field (VF) testing. MD improved by 5 dB or more in 34 of 70 total eyes (48.6%); VA improved by 0.2 logMAR (two lines on Snellen chart) or more in 21 eyes (30%), and by both in 15 eyes (21.4%). Final MD was -10 dB or better in 38 eyes (54.3%); final VA was 0.3 (6/12) or better in 54 eyes (77.1%), and both in 39 eyes (55.7%).

CONCLUSIONS

The results confirm that ONSF can relieve papilloedoema in both eyes and improve both VF and VA, even in cases of fulminant PTC with severe acute visual impairment.

Optic nerve sheath fenestration for visual impairment in cerebral venous diseases

Objective

Visual impairment is the most common clinical feature of cerebral venous sinus occlusion or cerebral venous thrombosis-induced intracranial hypertension, which can result in optic atrophy, leading to irreversible vision loss, visual field defections, and finally, permanent blindness. Papilledema is a typical early pathophysiological alteration in visual impairment. Optic nerve sheath fenestration (ONSF) has become increasingly accepted as an option to prevent or halt progressive visual loss owing to its low risk and complications. The objective of this study is to review the latest research progress on ONSF for the treatment of visual impairment related to cerebral venous diseases.

Methods

Study were searched following PRISMA guidelines based on three electronic databases (Pubmed, Embase and Medline-Ovid). We used the following keywords and variations as keywords to identify studies: "optic nerve sheath fenestration, papilledema, cerebral venous diseases, cerebral venous stenosis, cerebral venous thrombosis, idiopathic intracranial hypertension". The publication date of studies was restricted between 1,872.1.1 and 2,021.12.31. The application of ONSF in papilledema due to cerebral venous diseases is reviewed. Additionally, the common surgical approaches as well as advantages and disadvantages are also described graphically.

Results

With the improvement of specific details of the ONSF procedure and surgical instruments, complications of ONSF have reduced and its safety has been significantly improved, although the number of clinically investigated cases in the literature remains low.

Conclusion

We recommend that ONSF should be considered as an imperative alternative to reduce or delay the visual morbidity of cerebral venous diseases, although there is yet no consensus on the optimal surgical timing.

Acute Bilateral Vision Loss Following Unilateral Optic Nerve Sheath Fenestration

Optic nerve sheath fenestration (ONSF) is a surgical technique commonly and effectively employed in the treatment of recalcitrant, vision-threatening papilledema. Unilateral blindness, a known risk of unilateral ONSF widely cited with 1%-2% incidence. In this case, a 58-year-old patient who presented symptomatic with bilateral hemorrhagic papilledema unresponsive to medical therapy underwent uneventful unilateral ONSF via standard superomedial eyelid crease incision. The patient presented postoperatively with severe bilateral vision loss. Workup revealed widespread metastatic malignant disease involving the optic chiasm and optic nerve sheath.

Visual recovery after unilateral optic nerve sheath fenestration for pseudotumor cerebri syndrome

PURPOSE

To evaluate the effect of optic nerve sheath fenestration (ONSF) on the rate of visual function improvement in patients with pseudotumor cerebri syndrome (PTCS).

METHODS

Retrospective chart review of patients with PTCS who underwent ONSF between 1998 and 2017. Visual function was evaluated by evaluating visual field (VF), mean deviation (MD), retinal nerve fiber layer (RNFL) thickness, papilledema grade, and visual acuity (VA) prior to and after ONSF.

RESULTS

Seventeen female patients aged 17 to 36 years underwent unilateral ONSF. Follow-up averaged 40.1 months. VF MD improved steadily in both eyes up to 12 months. Average RNFL thickness improved in the operated eye from 347 ± 166 mm to 92 ± 27 mm (p < .001) and the non-operated eyes from 306 ± 165 mm to 109 ± 46 mm (p < .001). The grade of papilledema improved in the operated eye from 3.3 ± 1.3 to 0.3 ± 0.7 and the non-operated eye from 3.0 ± 1.6 to 0.18 ± 0.4. There was an exponential rate of improvement in papilledema and RNFL thickness, with the greatest improvement occurring within the first 30 days. Average visual acuity remained intact in both eyes before and after surgery.

CONCLUSIONS

ONSF in appropriately selected patients leads to rapid improvement in papilledema and a steady recovery in VF.

Update on Idiopathic Intracranial Hypertension Management

BACKGROUND

Idiopathic Intracranial Hypertension (IIH) is a secondary headache with a steadily growing incidence. Currently, there is little evidence to guide the treatment of IIH.

OBJECTIVE

To review the pathophysiology of IIH, with focus on the role of obesity as a risk factor, and the implications for new therapeutic perspectives.

METHODS

in this narrative review, we summarized the current knowledge on treatment options highlighting available evidence for managing intracranial hypertension, obesity, and headache.

RESULTS

Clinical Presentation: headache is the most common symptom and a significant cause of quality-of-life impairment. Visual loss is common in the diagnosis. Pathophysiology: there is no unified theory able to explain all symptoms and the evolution of the disease. There is growing data pointing to metabolic changes and obesity with a central role in IIH pathophysiology. Treatment: most published data on IIH treatment is related to pressure control and protection from visual loss. Acetazolamide and cerebrospinal fluid diversion are the best options available. Optic nerve sheath fenestration might be useful to temporally control the pressure over the optic nerve and thus protect from visual deterioration. Recently, venous sinus stenting has proven to be a safe option in selected cases. Finally, bariatric surgery has proven to effectively control elevated intracranial pressure.

CONCLUSION

IIH is a potential cause of high disability. Early recognition is important, and treatment should be tailored to the needs of each case. There is a lack of research on headache management, which might persist after ICP control.

New Options (or not) for Treatment of Idiopathic Intracranial Hypertension

PURPOSE OF REVIEW

Idiopathic intracranial hypertension (IIH) is a disorder primarily affecting obese women of childbearing age and, if left untreated, can lead to irreversible vision loss. No consensus exists on the best management strategy for IIH. Weight loss is advocated and few useful medical options exist. There is an unmet need to discover new treatment options for this increasingly prevalent condition. This article reviews the recent advances and research on the treatment of IIH.

RECENT FINDINGS

Venous sinus stenting (VSS) is now performed in many experienced centers, and there is growing interest in bariatric surgery as a treatment modality. Newly approved anti-obesity drugs are showing effectiveness in weight loss, and novel targeted disease-modifying IIH therapies are being explored. Further evaluation of these novel therapeutic strategies as well as studies exploring the use of anti-obesity drugs in IIH is needed. While VSS is gaining popularity due to its efficacy and low complication rate, there is insufficient evidence to support any surgical procedure over another. Bariatric surgery is appealing for patients with non-sight-threatening IIH and needs to be further explored.

Idiopathic Intracranial Hypertension - Challenges and Pearls

Idiopathic intracranial hypertension (IIH) is defined as a syndrome of raised intracranial pressure with normal imaging of the brain and cerebrospinal fluid (CSF) composition. There is a rising incidence and prevalence of this disease related to the increased prevalence of obesity. It typically affects women of working age, and headache is the predominant morbidity in over 90%. The disease is also more prevalent in young males. There are many controversies and myths that surround IIH. There are currently few treatment options for IIH, management is typically medical with those experiencing progressive visual loss undergoing surgical procedures. Weight loss and venous sinus stenting are a few therapies directed at the etiology.

Central Retinal Artery Visualization with Cone-Beam CT Angiography

Background There are multiple tools available to visualize the retinal and choroidal vasculature of the posterior globe. However, there are currently no reliable in vivo imaging techniques that can visualize the entire retrobulbar course of the retinal and ciliary vessels. Purpose To identify and characterize the central retinal artery (CRA) using cone-beam CT (CBCT) images obtained as part of diagnostic cerebral angiography. Materials and Methods In this retrospective study, patients with catheter DSA performed between October 2019 and October 2020 were included if CBCT angiography included the orbit in the field of view. The CBCT angiography data sets were postprocessed with a small field-of-view volume centered in the posterior globe to a maximum resolution of 0.2 mm. The following were evaluated: CRA origin, CRA course, CRA point of penetration into the optic nerve sheath, bifurcation of the CRA at the papilla, visualization of anatomic variants, and visualization of the central retinal vein. Descriptive statistical analysis was performed. Results Twenty-one patients with 24 visualized orbits were included in the analysis (mean age, 55 years ± 15; 14 women). Indications for angiography were as follows: diagnostic angiography (n = 8), aneurysm treatment (n = 6), or other (n = 7). The CRA was identified in all orbits; the origin, course, point of penetration of the CRA into the optic nerve sheath, and termination in the papilla were visualized in all orbits. The average length of the intraneural segment was 10.6 mm (range, 7-18 mm). The central retinal vein was identified in six of 24 orbits. Conclusion Cone-beam CT, performed during diagnostic angiography, consistently demonstrated the in vivo central retinal artery, demonstrating excellent potential for multiple diagnostic and therapeutic applications. © RSNA, 2021 Online supplemental material is available for this article.

Evaluation of the neuroprotective effects of methylprednisolone and surgical decompression in a rodent model of traumatic optic neuropathy

PURPOSE OF THE STUDY

Traumatic optic neuropathy (TON) is a rare but serious consequence of head injuries. The optimal therapy for TON remains controversial, and standardized recommendations are lacking. The most common therapies used are steroid administration and surgical decompression procedures. The aim of the present study was to compare two common conservative and surgical therapies in a rodent model with a standardized traumatic optic nerve lesion.

MATERIALS AND METHODS

This study employed 59 male Wistar rats. After exposing the optic nerve, defined trauma was exerted on the optic nerve using a micromanipulator to trigger TON. Rats received either "megadose" methylprednisolone applied perioperatively or decompression via nerve sheath fenestration. The number of neurons was histologically evaluated in retinae explanted as whole mounts. Neuronal size was determined histomorphometrically.

RESULTS

Neuronal loss was significantly lower following perioperative "megadose" steroid therapy (p = 0.017), especially in the central retinal area (p = 0.025). Compared to the control group without therapy, on average more than 400 neurons/mm² were saved. In the central retinal area, more than 600 neurons/mm² were rescued. In contrast, neuronal loss was not significantly affected by surgical decompression; however, this procedure was associated with a reduction in neuron size (p = 0.003).

CONCLUSIONS

The present model revealed significant neuroprotective effects following administration of methylprednisolone for TON treatment. Mitigation of neuronal loss may result in functional benefits. Neuroprotective effects were not observed following surgical therapy, suggesting that this approach should be reserved for individual cases such as hematomas in the area of nerve envelopes.

A 270-Degree Decompression of Optic Nerve in Refractory Idiopathic Intracranial Hypertension Using an Ultrasonic Aspirator - A Prospective Institutional Study

Background

Although the nonsurgical treatment for idiopathic intracranial hypertension (IIH) involves weight loss, diuretics, and steroids, surgical intervention is required if there is a worsening of symptoms or visual deterioration.

Objective

To determine the efficacy and complications of transcranial optic nerve sheath fenestration (ONSF) using an ultrasonic aspirator as an adjunct in the treatment of refractory IIH.

Material and Methods

This prospective study included all patients with medically refractory IIH with visual deterioration from November 2017 to June 2019. Pterional craniotomy was followed by extradural clinoidectomy and optic foramen bony decompression using an ultrasonic aspirator. All the cases were followed up for changes in visual acuity and field and surgical outcomes.

Results

A total of 21 consecutive patients who underwent ONSF in the study period were included for analysis. Improvement in visual acuity was noted in 19/21 (90.47%) patients. Improvement in visual fields was noted in 17/21 (80.95%). Headache improved in 66.67% of patients. Improvement in the fundus picture was noted in 90.47%. Symptoms < 6 months showed better results compared to > 6 months symptom, although statistically nonsignificant (P = 0.2556). A 270-degree optic canal decompression was achieved in all the cases.

Conclusion

Transcranial optic nerve sheath decompression with a bone ultrasonic aspirator is a safe and direct decompression of the optic nerve in malignant/refractory cases of IIH.

Role of Optic Nerve Sheath Fenestration in Inflammatory Pachymeningitis Causing Visual Impairment

Eye disease due to pachymeningitis caused by immunoglobulin G4-related disease (IgG4-RD) is a rare occurrence. Here, the authors report a unique case of a patient presenting with visual loss from raised intracerebral pressure from pachymeningitis most likely related to IgG4-RD. The patient was treated with acetazolamide and steroids, and an optic nerve sheath fenestration was performed to successfully save the patients vision.

Endoscopic Bilateral Optic Nerve Decompression for Treatment of Idiopathic Intracranial Hypertension

Objective: To evaluate the results of bilateral endoscopic optic nerve decompression (EOND) with the opening nerve sheath (ONS) technique in patients with idiopathic intracranial hypertension (IIH). Methods: Between the years of 2017 and 2019, we retrospectively evaluated nine IIH patients with progressive visual impairment despite medical treatment and who were treated with the EOND and ONS techniques. We also demonstrated our surgical technique recipe on postmortem human heads in a stepwise manner. Results: There were 9 patients (7 females and 2 males) between the ages of 21 and 72 included in this study, and the mean age was 40.8. All patients had an impairment in visual acuity and/or their visual field, with signs of papilledema and/or optic atrophy. The patients were followed up with for 9–48 months. Improvements in visual acuity were observed in 7 out of 9 patients (78%). Visual field defects improved in 5 out of 8 patients (62.5%). Papilledema was resolved in all patients (100%). Headaches improved in all symptomatic patients (100%). No intraoperative or postoperative complications were observed. Conclusions: EOND is a safe and effective surgical procedure in selected patients with IIH. Bilateral wide bony decompression and nerve fenestration can also be an additional benefit for headache relief. Further clinical series and long-term follow-up are needed for more precise results.

Reviewing the Recent Developments in Idiopathic Intracranial Hypertension

There is increasing evidence and appreciation of idiopathic intracranial hypertension (IIH) in medicine. The pathological processes underlying raised intracranial pressure are being studied, with new insights found in both hormonal dysregulation and the metabolic neuroendocrine axis. These will potentially lead to novel therapeutic targets for IIH. The first consensus guidelines have been published on the investigation and management of adult IIH, and the International Headache Society criteria for headache attributable to IIH have been modified to reflect our evolving understanding of IIH. Randomized clinical trials have been published, and a number of studies in this disease area are ongoing.

Transient vision loss after optic nerve sheath fenestration

Optic nerve sheath fenestration (ONSF) is a well-known, relatively safe, and effective surgical treatment for visual loss related to papilledema. Visual loss following ONSF is uncommon but can occur from direct surgical trauma, ischemic optic neuropathy, orbital or intrasheath hemorrhage, or arterial occlusion. Transient severe (e.g., light perception (LP) or no light perception (NLP) visual loss) after ONSF is uncommon but has been reported. We describe a case of LP vision following uncomplicated ONSF with orbital imaging demonstrating significant postoperative inflammation and slow recovery after intravenous steroid treatment. We discuss the various mechanisms for this phenomenon after ONSF. To our knowledge, this is the first clinico-radiologic description with follow up and recovery of this postoperative complication of ONSF to be reported in the English language ophthalmic literature.

Presentation and Progression of Papilledema in Cerebral Venous Sinus Thrombosis

PURPOSE

To determine the natural history and visual outcomes of papilledema in cerebral venous sinus thrombosis (CVST).

DESIGN

Retrospective observational case series.

METHODS

This multicenter study included 7 tertiary care neuro-ophthalmology clinics. Sixty-five patients with CVST were identified who received serial eye examinations with documented papilledema from 2008-2016. Outcome measures included time from diagnosis to papilledema documentation, papilledema progression, time to papilledema resolution, treatment interventions and final visual outcomes.

RESULTS

Papilledema was present on initial presentation in 54% of patients or detected later during the course of the disease in 46% of patients. The average time from CVST diagnosis to papilledema documentation was 29 days with a mean (SD) initial Frisén grade of 2.7 (1.3). In 21.5% of cases, papilledema progressed over an average of 55.6 (56.6) days. Time to papilledema resolution was approximately 6 months. Final visual acuity ranged from 20/20 to light perception, with 40% of patients having residual visual field defects on standard automated perimetry. Frisén grade ≥3 (odds ratio [OR] 10.21, P < .0053) and cases with worsening papilledema (3.5, P < .043) were associated with permanent visual field deficits.

CONCLUSIONS

Our study indicates the importance of serial ophthalmic evaluation in all cases of CVST. Follow-up fundoscopy is critical given that a subset of cases can show delayed onset and/or worsening of papilledema with time. Specifically, we recommend an ophthalmic examination at the time of initial diagnosis, with repeat examination within a few weeks and further follow-up depending on the level of papilledema or vision changes.

Fulminant Idiopathic Intracranial Hypertension

PURPOSE OF REVIEW

The goal of this review is to describe the presenting features of fulminant idiopathic intracranial hypertension (IIH) and outline the multimodal approach to its treatment.

RECENT FINDINGS

Venous sinus stenting may be an appropriate alternative to optic nerve sheath fenestration or cerebrospinal fluid shunting in select patients with fulminant IIH. Prompt surgical intervention maximizes the chance of visual recovery in patients with fulminant IIH. "Fulminant IIH" is defined as intracranial hypertension with no secondary cause, severe vision loss within 4 weeks of symptom onset, and progressive vision loss over days. Rapid recognition of the fulminant phenotype of IIH by emergency department physicians, neurologists, and ophthalmologists is critical. Without appropriate triage and rapid medical and surgical intervention, patients with fulminant IIH are at high risk for profound, permanent vision loss. Prompt surgical intervention with optic nerve sheath fenestration, cerebrospinal fluid shunting, or venous sinus stenting minimizes the chance of poor visual outcome. If a delay is anticipated, serial lumbar punctures or temporary cerebrospinal fluid drainage and medical therapy may forestall irreversible vision loss.

Exploring The Current Management Idiopathic Intracranial Hypertension, And Understanding The Role Of Dural Venous Sinus Stenting

Idiopathic Intracranial Hypertension (IIH) is a debilitating disorder characterised by raised intracranial pressure (ICP), papilloedema with the potential risk of permanent visual loss, and headaches that are profoundly disabling and reduce the quality of life. The first consensus guidelines have been published on investigation and management of adult IIH and one key area of uncertainty is the utility of dural venous sinus stenting for the management of headache and visual loss. There are an increasing number of series published and to help understand the successes and complications. During a patient physician priority setting, the understanding of the best type of intervention to treat IIH was assigned to the top 10 of most desired research questions for the disease. Ultimately randomised clinical trials (RCTs) in neurovascular stenting for IIH would be instructive, as the literature to date may suffer from publication bias. Due to the increasing incidence of IIH, there is no better time to systematically investigate interventions that may reverse the disease process and achieve remission. In this review we discuss the pathophysiology of IIH in relation to venous sinus stenosis, the role of venous sinus stenting with a review of the relevant literature, the advantages and disadvantages of stenting compared with other surgical interventions, and the future of stenting in the treatment of IIH.

Update on the Diagnosis and Treatment of Idiopathic Intracranial Hypertension

Advances in ophthalmic diagnostics and results of interventional clinical trials are shifting diagnosis and management of idiopathic intracranial hypertension (IIH) to be more technology- and evidence-based. In this article, the evidence supporting current diagnostic criteria, evaluation, and medical and surgical management of IIH are reviewed.

An evolving perspective of endoscopic transnasal optic canal decompression for traumatic optic neuropathy in clinic

Traumatic optic neuropathy (TON) is a serious complication of craniofacial trauma, which damages the optic nerve indirectly and leads to dysfunction of visual acuity. The clinical intervention for a patient with TON includes optic canal decompression (with or without steroids), treatment with corticosteroids alone, or observation only. Currently, there is a controversy among clinicians as to which treatment is optimal. An increasing number of retrospective studies have unveiled that patients could experience significant improvement in visual acuity after optic canal decompression surgery, particularly endoscopic transnasal/transethmosphenoid optic canal decompression (ETOCD), either with or without corticosteroids. In this review, we discuss the evolving perspective on surgical treatment, specifically ETOCD, for the management of patients with TON and focus mainly on the therapeutic efficacy, safety, and resulting prognosis in the clinic.

Clinical and Magnetic Resonance Imaging Characteristics of Postfenestration Optic Nerve Sheath Pseudomeningoceles

PURPOSE

The clinical significance of postoperative pseudomeningocele formation following optic nerve sheath fenestration (ONSF) has not been fully characterized. A literature review identifies 9 previously published cases the authors believe demonstrate pseudomeningocele formation and approximately 19 other similar findings that were either transient or less defined blebs. This study was undertaken to more clearly define the clinical, radiographic, and histopathologic features associated with this entity.

METHODS

Sixteen-year, single-center, retrospective chart review of all ONSF cases performed by 2 surgeons. Clinical data, intracranial pressure, radiographic imaging, and histopathology of clinically detected pseudomeningoceles after ONSF were reviewed.

RESULTS

Eighty-six eyes in 57 patients underwent ONSF (28 unilateral, 12 bilateral sequential, 17 bilateral simultaneous). Forty-nine of 57 patients had elevated intracranial pressure preoperatively (41 idiopathic intracranial hypertension, 4 venous thrombosis, 2 meningitis, 1 arteriovenous malformation, and 1 sarcoid). In 32 patients undergoing postoperative imaging, 4 eyes (4.7%) in 4 patients developed well-defined pseudomeningoceles, of which 3 were symptomatic and 2 required surgical revision. Each pseudomeningocele developed in the setting of elevated preoperative intracranial pressure (350, 360, 430, 500 mm H20). Magnetic resonance imaging and/or computed tomography revealed sharply demarcated fluid-filled sacs adjacent to the optic nerve. The contents of these sacs were hypointense on T1-weighted imaging, hyperintense on T2-weighting, variably enhanced with contrast, and hypointense on fluid attenuated inversion recovery, and were thus consistent with cerebrospinal fluid. Histopathologic analysis of one of these outpouchings demonstrated an acellular, fibrocollagenized lining consistent with pseudomeningocele. Three eyes in 3 additional patients had less well-defined findings on imaging interpreted as bleb-like or cyst-like change.

CONCLUSIONS

Pseudomeningoceles following ONSF may be asymptomatic or may cause symptomatic orbital mass effect and rarely visual loss, amendable to surgical excision. Post-ONSF pseudomeningoceles are identified on computed tomography or magnetic resonance imaging to occur at the locations of fenestration sites and contain cerebrospinal fluid communicating with the subdural space that may act as a "filtration" bleb in some cases. Imaging findings may represent a spectrum spanning intraorbital cerebrospinal fluid leakage, partial walling off of bleb, or fully developed cysts. Resection of optic nerve pseudomeningoceles is considered in symptomatic cysts or eyes with papilledema that fails to improve.