Long-term results using adjunctive mitomycin C in optic nerve sheath decompression for pseudotumor cerebri

Novel Approaches to the Treatment of Idiopathic Intracranial Hypertension

PURPOSE OF REVIEW

Idiopathic intracranial hypertension (IIH) typically affects women of childbearing age, is associated with recent weight gain, and can result in debilitating headache as well as papilledema that can cause vision loss. There have been advances in the medical and surgical treatment of affected patients with IIH that can improve outcomes and tolerability of therapy.

RECENT FINDINGS

Medical treatment with agents that lower intracranial pressure through pathways other than carbonic anhydrase inhibition are being developed, and medically-directed weight loss as well as bariatric surgery now may be considered as primary therapy. New surgical options including venous sinus stenting have shown efficacy even with cases of severe vision loss. Our treatment options for IIH patients are becoming more diverse, and individualized treatment decisions are now possible to address specific components of the patient's disease manifestations and to lead to IIH remission.

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.

The Role of Mitomycin C in Preventing Synechia and Stenosis after Endoscopic Sinus Surgery

Background

Synechia and stenosis formation after endoscopic sinus surgery (ESS) represents a potential source of surgical failure. Mitomycin C (MMC) has been used successfully in other fields to decrease postoperative scar formation. We hypothesize that the topical application of MMC reduces the incidence of stenosis and synechia formation after ESS.

Methods

This study is a randomized, controlled, single-blinded study based in a tertiary care teaching hospital. After routine ESS, a pledget soaked in MMC (0.5%) was randomly placed into the middle meatus of one nasal cavity for 5 minutes and a pledget soaked in saline was placed in the contralateral side in each patient. A blinded observer followed the patients for any evidence of stenosis or synechia formation. The medical records of enrolled patients were reviewed for demographics, diagnosis, prior surgery, type of sinus surgery, complications, incidence of stenosis/synechia, and need for further procedures.

Results

Twenty-nine patients were included in the final analysis. The mean follow-up period was 15 months (range, 3–32 months). There were no complications in this series. Eight patients experienced 10 episodes of synechia formation and one patient experienced 1 episode of synechia formation and 1 episode of stenosis of the maxillary sinus ostium. Seven of the 12 episodes of synechia/stenosis occurred on the side of the MMC application and the remaining 5 episodes occurred on the side opposite to the MMC application. This difference was not statistically significant.

Conclusion

The topical application of MMC did not decrease the incidence of stenosis and synechia formation after ESS. (American Journal of Rhinology 18, 311–314, 2004)

A 15-year review of secondary and tertiary optic nerve sheath fenestration for idiopathic intracranial hypertension

PURPOSE

Optic nerve sheath fenestration (ONSF) is a common surgical option for patients with idiopathic intracranial hypertension (IIH) with vision loss refractory to medical management. Little is known about the visual benefit of repeated ONSF. The authors aimed to assess the efficacy of secondary and tertiary ONSF in patients with IIH.

METHODS

A retrospective chart review was performed on all patients with repeat ONSF for IIH at Emory University from 1999 to 2016. Primary outcome measures included visual acuity, optic nerve head findings, and visual field results.

RESULTS

A total of nine eyes in seven patients (five females and two males) with repeat ONSF were identified. Two of the seven patients had repeat ONSF in both eyes, while the remaining five patients had only one eye repeated. Five of seven patients (five eyes) improved or remained stable after the secondary ONSF. Two patients (three eyes) continued to worsen despite the secondary fenestration surgery and underwent tertiary ONSF at an average of 13.2 months (SD 5.5 months) after the failed secondary ONSF. Both patients that underwent the tertiary fenestration showed improvement. Six of the patients had either improvement or stability in their clinical findings at their last documented follow-up, but one continued to worsen despite intervention.

CONCLUSIONS

This study suggests that secondary and tertiary nerve sheath fenestration is a viable management option for patients with progressive vision loss from IIH. Repeat ONSFs do not appear to have increased complication or failure rates compared to prior documented studies regarding primary fenestrations.

Idiopathic Intracranial Hypertension. A Systematic Analysis of Transverse Sinus Stenting

BACKGROUND

Idiopathic intracranial hypertension (IIH) is a disorder characterized by signs and symptoms of increased intracranial pressure without structural cause seen on conventional imaging. Hallmark treatment after failed medical management, has been CSF shunting or optic nerve fenestration with the goal of treatment being preservation of vision. Recently, there have been multiple case reports and case series on dural sinus stenting for this disorder.

OBJECTIVE

We aim to review all published cases and case series of dural sinus stenting for IIH, with analysis of patient presenting symptoms, objective findings (CSF pressures, papilledema, pressure gradients across dural sinuses), follow-up of objective findings, and complications.

METHODS

A Medline search was performed to identify studies meeting pre-specified criteria of a case report or case series of patients treated with dural sinus stent placement for IIH. The manuscripts were reviewed and data was extracted.

RESULTS

A total of 22 studies were identified, of which 19 studies representing 207 patients met criteria and were included in the analysis. Only 3 major complications related to procedure were identified. Headaches resolved or improved in 81% of patients. Papilledema improved the (172/189) 90%. Sinus pressure decreased from an average of 30.3 to 15 mm Hg. Sinus pressure gradient decreased from 18.5 (n=185) to 3.2 mm Hg (n=172). Stenting had an overall symptom improvement rate of 87%.

CONCLUSION

Although all published case reports and case series are nonrandomized, the low complication and high symptom improvement rate make dural sinus stenting for IIH a potential alternative surgical treatment. Standardized patient selection and randomization trials or registry are warranted.

Venous sinus stenting for idiopathic intracranial hypertension: a review of the literature

Idiopathic intracranial hypertension (IIH) is characterized by headache, papilledema, visual field changes and tinnitus with elevated cerebral spinal fluid opening pressures on lumbar puncture. Left untreated, this condition can lead to permanent visual loss. Previous treatment modalities include medical management, therapeutic lumbar puncture and optic nerve sheath fenestration. They have proved to be effective but carry high rates of symptom recurrence or procedural complications. Focal dural venous sinus stenoses have been identified in many patients with IIH, leading to development of treatment through venous sinus angioplasty and stenting. A review of the literature was performed which identified patients with IIH treated with venous sinus stenting. The procedural data and outcomes are presented. A total of 143 patients with IIH (87% women, mean age 41.4 years, mean body mass index 31.6 kg/m(2)) treated with venous sinus stenting were included in the analysis. Symptoms at initial presentation included headache (90%), papilledema (89%), visual changes (62%) and pulsatile tinnitus (48%). There was a technical success rate of 99% for the stent placement procedure with a total of nine complications (6%). At follow-up (mean 22.3 months), 88% of patients experienced improvement in headache, 97% demonstrated improvement or resolution of papilledema, 87% experienced improvement or resolution of visual symptoms and 93% had resolution of pulsatile tinnitus. In patients with IIH with focal venous sinus stenosis, endovascular stent placement across the stenotic sinus region represents an effective treatment strategy with a high technical success rate and decreased rate of complications compared with treatment modalities currently used.

Dural sinus stent placement for idiopathic intracranial hypertension

Object

The use of unilateral dural sinus stent placement in patients with idiopathic intracranial hypertension (IIH) has been described by multiple investigators. To date there is a paucity of information on the angiographic and hemodynamic outcome of these procedures. The object of this study was to define the clinical, angiographic, and hemodynamic outcome of placement of unilateral dural sinus stents to treat intracranial venous hypertension in a subgroup of patients meeting the diagnostic criteria for IIH.

Methods

Eighteen consecutive patients with a clinical diagnosis of IIH were treated with unilateral stent placement in the transverse-sigmoid junction region. All patients had papilledema. All 12 female patients had headaches; 1 of 6 males had headaches previously that disappeared after weight loss. Seventeen patients had elevated opening pressures at lumbar puncture. Twelve patients had opening pressures of 33–55 cm H2O. All patients underwent diagnostic cerebral arteriography that showed venous outflow compromise by filling defects in the transverse-sigmoid junction region. All patients underwent intracranial selective venous pressure measurements across the filling defects. Follow-up arteriography was performed in 16 patients and follow-up venography/venous pressure measurements were performed in 15 patients.

Results

Initial pressure gradients across the filling defects ranged from 10.5 to 39 mm Hg. Nineteen stent procedures were performed in 18 patients. One patient underwent repeat stent placement for hemodynamic failure. Pressure gradients were reduced in every instance and ranged from 0 to 7 mm Hg after stenting. Fifteen of 16 patients in whom ophthalmological follow-up was performed experienced disappearance of papilledema. Follow-up arteriography in 16 patients at 5–99 months (mean 25.3 months, median 18.5 months) showed patency of all stents without in-stent restenosis. Two patients had filling defects immediately above the stent. Four other patients developed transverse sinus narrowing above the stent without filling defects. One of these patients underwent repeat stent placement because of hemodynamic deterioration. Two of the other 3 patients had hemodynamic deterioration with recurrent pressure gradients of 10.5 and 18 mm Hg.

Conclusions

All stents remained patent without restenosis. Stent placement is durable and successfully eliminates papilledema in appropriately selected patients. Continuing hemodynamic success in this series was 80%, and was 87% with repeat stent placement in 1 patient.

Idiopathic intracranial hypertension: lumboperitoneal shunts versus ventriculoperitoneal shunts--case series and literature review

OBJECTIVES

Idiopathic intracranial hypertension (IIH) is an uncommon but important cause of headache that can lead to visual loss. This study was undertaken to review our experience in the treatment of IIH by neuronavigation-assisted ventriculoperitoneal (VP) shunts with programmable valves as compared to lumboperitoneal (LP) shunts.

METHODS

A retrospective chart review was conducted on 25 patients treated for IIH between 2001 and 2009. Age, sex, clinical presentation, methods of treatment and failure rates were recorded.

RESULTS

Seventy-two per cent were treated initially with LP shunts. Failure rate was 11% in this group. Neuronavigation-assisted VP shunts were used to treat 28%. In this group, the failure rate was 14%.

CONCLUSION

Our experience indicates that both LP shunts and VP shuts are effective in controlling all the clinical manifestations of IIH in the immediate postoperative period. Failure rates are slightly higher for VP shunts (14%) than LP shunts (11%). However, revision rates are higher with LP shunts (60%) than with VP shunts (30%).

Idiopathic intracranial hypertension in children: a review and algorithm

This updated review of pediatric idiopathic intracranial hypertension focuses on epidemiology, clinical presentations, diagnostic criteria, evaluation, clinical course, and treatment. General guidelines for the clinical management of idiopathic intracranial hypertension are discussed. A new algorithm outlines an efficient management strategy for the initial diagnostic evaluation of children with signs or symptoms of intracranial hypertension. This algorithm provides a systematic approach to initial evaluation and management, and identifies important decision-making factors. The risk of permanent visual loss with idiopathic intracranial hypertension necessitates a prompt, thorough collaborative approach in the management of patients. Although idiopathic intracranial hypertension has been recognized for over a century, the need remains for prospectively collected data to promote a better understanding of the etiology, risk factors, evaluative methods, and effective treatments for children with this syndrome.

Localized Cystic Enlargement of the Distal Optic Nerve Sheath after Decompression Surgery

Cystic formation of the optic meninges may occur after optic nerve sheath decompression surgery for the management of pseudotumor cerebri. A case with a cyst-like structure of the distal optic nerve sheath at the operation site in the late surgical period after nerve sheath decompression surgery is reported.

Clinical review: the surgical treatment of idiopathic pseudotumour cerebri (idiopathic intracranial hypertension)

To review the literature on the surgical treatment of idiopathic pseudotumour cerebri (PTC) [idiopathic intracranial hypertension (IIH)]. When medical therapy fails or when visual dysfunction deteriorates, surgical therapies for PTC should be considered. The main procedures performed include lumboperitoneal shunt (LPS), ventriculoperitoneal shunt (VPS) and optic nerve sheath fenestration (ONSF). Recently, venous sinus stenting procedures have been performed on selected patients with PTC, especially those with venous sinus occlusive disease. The literature is summarized and appraised in the form of a narrative review. It is evident that ONSF, LPS, VPS and, in selected cases, venous sinus stenting may improve vision and prevent deterioration of vision in patients with PTC. All of the procedures have their advantages and disadvantages and may fail with time no matter what procedure is used. Various authorities have vehemently advocated one or the other of these procedures. Until a prospective, randomized study comparing ONSF with LPS or VPS for PTC is performed, and until the role of venous sinus obstruction as the aetiology of PTC is better defined, the question of which surgical procedure is best for the treatment of PTC remains unanswered.

Findings of magnetic resonance imaging after optic nerve sheath decompression in patients with idiopathic intracranial hypertension

PURPOSE

To evaluate morphologic changes occurring in the retrobulbar region after optic nerve sheath decompression (ONSD) in patients with idiopathic intracranial hypertension using magnetic resonance (MR) imaging.

DESIGN

Prospective observational study.

METHODS

This study included 26 eyes of 17 patients (age range, nine to 57 years) with idiopathic intracranial hypertension who underwent ONSD. The surgery was performed through transconjunctival medial orbitotomy and by a dural window excision. After ONSD, the optic nerves were examined with MR imaging by means of 3-dimensional "constructive interference in steady state" (CISS) sequence.

RESULTS

After ONSD, papilledema resolved in all eyes and visual functions improved in all except one. Early postoperative MR imaging (two to eight weeks after surgery) demonstrated a cyst-like fluid collection adjacent to the dural window site in nine (75%) of 12 eyes and a fibrous tissue formation in three eyes (25%). Late postoperative MR imaging (six to 15 months after surgery) demonstrated a fibrous tissue formation at the decompression site in 25 eyes (96%) and perioptic fluid collection in one eye (4%).

CONCLUSIONS

In early postoperative period after ONSD, a fluid collection adjacent to the decompression site occurs in most eyes; this finding disappears in late period. Early postoperative MR findings support the idea that ONSD functions through the cerebrospinal fluid (CSF) filtration.

Mitomycin: clinical applications in ophthalmic practice

Mitomycin (mitomycin C; MMC) is an antibiotic isolated from Streptomyces caespitosus. The drug is a bioreductive alkylating agent that undergoes metabolic reductive activation, and has various oxygen tension-dependent cytotoxic effects on cells, including the cross-linking of DNA. It is widely used systemically for the treatment of malignancies, and has gained popularity as topical adjunctive therapy in ocular and adnexal surgery over the past 2 decades. In ophthalmic medicine, it is principally used to inhibit the wound healing response and reduce scarring of surgically fashioned ostia. Hence, it has been used as adjunctive therapy in various ocular surgeries, such as glaucoma filtering surgeries, dacryocystorhinostomy, corneal refractive surgery and surgeries for ocular cicatrisation. In addition, it has been used as an adjunct in the surgical management of pterygia, ocular surface squamous neoplasia, primary acquired melanosis with atypia and conjunctival melanoma. In many of these surgeries and ophthalmic pathologies, MMC showed a significant beneficial effect.

Optic nerve sheath fenestration with endoscopic accessory instruments versus the free electron laser (FEL)

BACKGROUND AND OBJECTIVE

The free electron laser (FEL) can efficiently produce an optic nerve sheath fenestration using an endoscopic approach. To develop a surgical protocol, this study compared effectiveness of available accessory endoscopic instruments to endoscopic FEL delivery effectiveness in producing optic nerve sheath fenestrations.

STUDY DESIGN/MATERIALS AND METHODS

An endoscope was used to perform optic nerve sheath fenestrations on goat optic nerves. Accessory endoscopic instruments and glass-hollow waveguides (250 and 320 microm in diameter) were inserted into the instrument channel for comparison. FEL energy (6.45 microm, 30 Hz) was delivered to the tissue through the waveguides and histological analysis was performed.

RESULTS

The endoscopic instruments alone were unable to incise the optic nerve sheath. The FEL successfully incised the sheath and the biopsy forceps extricated the circular flap.

CONCLUSIONS

Endoscopic optic nerve sheath fenestration using FEL energy followed by biopsy forceps for sheath extrication produced good results, thereby creating a feasible protocol for optic nerve sheath fenestration.

Optic nerve disorders: role of canal and nerve sheath decompression surgery

Optic nerve sheath decompression (ONSD) maintains a role in the management of visual loss complicating papilloedema in selected patients primarily with idiopathic intracranial hypertension. The evidence base for this intervention is reviewed and audit data on visual outcomes for patients with acute, chronic, and atrophic forms of papilloedema are contrasted. Optic canal decompression has a role in the management of compressive optic neuropathies complicating mass lesions arising from paranasal sinuses and intracranially and can be achieved by transethmoidal, transbasal, and open craniotomy routes. The evidence base supporting this intervention in traumatic optic neuropathy and in primary bone disease causing canal stenosis (in particular fibrous dysplasia) is reviewed where the indications are more controversial.

Recent developments in idiopathic intracranial hypertension (IIH)

Idiopathic intracranial hypertension is a disease with a predilection for young obese women. The most common symptoms are headache, transient visual obscuration and pulsatile tinnitus. The only focal neurologic finding is false-localizing 6th cranial nerve palsy. Papilledema is usually present and this can lead to optic atrophy with progressive permanent visual loss. The earliest visual loss is constriction of peripheral visual field, usually starting with the inferior nasal quadrant. Numerous theories have been entertained as to the pathogenesis but this still remains an open controversy. The most prevalent current theories involve increased resistance to cerebrospinal fluid reabsorption at the arachnoid granulations, either from intrinsic disease in the granulations or secondary to elevated pressure in the dural venous sinuses into which the cerebrospinal fluid is absorbed across the granulations. The syndrome of idiopathic intracranial hypertension was long ago recognized as a complication of recurrent otitis media with resultant thrombosis of the transverse and sigmoid dural venous sinuses. Cases secondary to dural venous sinus thrombosis are seldom encountered today because the incidence of chronic otitis is much less than in the past. The prevalent concept has been that the idiopathic cases in obese young women were not associated with pathology in the dural venous sinuses. A recent study using ATECO MR venography, which the authors claim to be more reliable than even conventional catheter venography, has demonstrated stenosis of the transverse and sigmoid dural venous sinuses distinguishes cases of idiopathic intracranial hypertension from controls with a high degree of sensitivity and specificity. The authors believe the stenosis is secondary to intracranial hypertension but that it may further aggravate the hypertension when it occurs.

Mitomycin C for the prevention of adhesion formation after endoscopic sinus surgery: a randomized, controlled study

OBJECTIVE

Mitomycin C (MMC) is an antineoplastic agent that has been shown to decrease scar tissue after ophthalmologic surgery. Our goal was to determine whether the application of MMC at the conclusion of sinus surgery decreases the incidence of postoperative adhesion formation.

METHODS

At the completion of endoscopic sinus surgery in 55 patients, a cotton pledget saturated with 1 mL of 0.4 mg/mL MMC was placed for 4 minutes in the right or left middle meatus and a similar saline-soaked pledget was placed on the opposite side. Patients were examined postoperatively by a masked observer for the presence of synechiae and mucosal changes.

RESULTS

Postoperative adhesions were observed in 16 patients (29%) with a mean follow-up of 4.1 months. These adhesions were bilateral in 6 patients (10.9%) and unilateral in 10 patients (18%). Unilateral adhesions were observed on only 2 sides (3.6%) treated with MMC and 8 controls (14.5%) (P = 0.058). No adverse effects were observed.

CONCLUSIONS

MMC was found to be safe to use during sinus surgery, and it may reduce the incidence of postoperative adhesions at the dosage used in this study.

SIGNIFICANCE

Because of the observed trend toward decreased synechiae formation with MMC application, further trials using higher concentrations and application times are warranted.

Histopathology and ultrastructural examination of optic nerve sheath biopsies after optic nerve sheath decompression with and without mitomycin

PURPOSE

We chose to compare histologically and ultrastructurally changes in the optic nerve sheath after optic nerve sheath decompression, initially after a second surgery and after treatment with mitomycin-C. The mechanism by which optic nerve sheath decompression alleviates papilledema can be further understood in consideration of the results.

METHODS

Tissue was obtained by biopsy from 3 first-time surgical and 4 reoperative cases with and without mitomycin-C in patients with idiopathic intracranial hypertension. The sheaths were fixed in a mixture of 2% paraformaldehyde and 2% glutaraldehyde, osmicated and dehydrated in a series of ethanol, and finally embedded in epon. Tissue blocks were sectioned at 1 microm and stained with both PPD and toluidine blue. Thin sections were examined by transmission electron microscopy.

RESULTS

Normal meningeal tissue obtained at the time at optic nerve sheath decompression consisted mainly of collagen, closely packed and roughly parallel to the axis of the optic nerve. Collagen deposition seen in scar tissue after secondary optic nerve sheath decompression was extremely disorganized and irregular, with the individual fibers laid down seemingly at random. There was little sense of layering or of parallel arrays. Mitomycin-C appeared to influence collagen deposition in such a way that the collagen was more regularly packed and more closely resembled unoperated tissue.

CONCLUSIONS

The regular well-organized collagen packing seen in normal sheath tissue is disrupted and replaced by less organized but compact scar tissue after optic nerve sheath decompression. With mitomycin use, more regular collagen packing closely approximating that found in unoperated sheath occurs. This configuration of fibers lends support for the filtration mechanism of optic nerve sheath decompression in treating papilledema.

Optic nerve sheath fenestration with a novel wavelength produced by the free electron laser (FEL)

BACKGROUND AND OBJECTIVE

To determine whether 6.45-microm free electron laser (FEL) energy can successfully perform optic nerve sheath fenestration and to compare the acute and chronic cellular responses with this surgery.

STUDY DESIGN/MATERIALS AND METHODS

Optic nerve sheath fenestration was performed in rabbits by using either FEL energy (< 2.5 mJ, 10 Hz, 325-microm spot size) or a knife. The optic nerve integrity and glial response were evaluated histologically acutely or 1 month postoperatively.

RESULTS

The FEL at low energy effectively cut the optic nerve sheaths with minimal reaction in the underlying nerve. With FEL or knife surgical techniques, a mild astrocytic hypertrophy only adjacent to the fenestration was observed acutely in the glial fibrillary acidic protein (GFAP) -immunoreacted sections. The chronic healing responses after either technique appeared similar with: (1) a thin fibrous scar at the fenestration site, (2) cells uniformly distributed (hematoxylin and eosin), and (3) up-regulation of GFAP and S100beta in astrocytes adjacent to the fenestration site.

CONCLUSION

The FEL at low energy performs an optic nerve sheath fenestration in a small space with ease. Both FEL and knife incisions cause a similar rapid glial response near the fenestration site that remains 1 month later.

Effect of mitomycin C on the optic nerve in rabbits

AIM

To prevent scarring after surgical optic nerve sheath decompression, it has been suggested that treating the area of fenestration with mitomycin C (MMC) might be effective. An animal model was used to test whether this toxic substance may cause optic neuropathy.

METHODS

The optic nerves of 15 rabbits were exposed to balanced salt solution (BSS) or mitomycin C (MMC) in a concentration of 0.2 or 0.5 mg/ml. The unoperated fellow eyes and the eyes that received BSS served as controls. Steady state visual evoked potentials (VEPs) at 40, 50, and 60 Hz were recorded before and 4 weeks after surgery. The nerves were examined by light and electron microscopy after 5 weeks.

RESULTS

VEPs in all non-operated eyes and eyes treated with BSS before and 4 weeks after surgery demonstrated responses at all three stimulus frequencies tested. Eyes operated with MMC had extinguished responses for one, two, or all the different temporal frequencies after 4 weeks with marked reduction in VEP amplitude. Eyes operated with MMC at a concentration of 0.5 mg/ml had significantly more reduced VEP responses than those where MMC 0.2 mg/ml was used. On histopathological examination, special stains for myelin and axons showed normal axons and myelin. On electron microscopy, no distinct abnormalities were seen among nerves operated with MMC and controls.

CONCLUSION

The data from this study suggest that in rabbits, the application of MMC to the optic nerve has a dose dependent toxic effect in the short term postsurgical follow up period. While a functional alteration could be demonstrated reproducibly by steady state VEPs, the extent was not obvious on histopathological examination of the nerves.