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

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.

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.

Characterization of the mechanical behavior of the optic nerve sheath and its role in spaceflight-induced ophthalmic changes

Visual impairment and intracranial pressure (VIIP) syndrome is characterized by a number of permanent ophthalmic changes, including loss of visual function. It occurs in some astronauts during long-duration spaceflight missions. Thus, understanding the pathophysiology of VIIP is currently a major priority in space medicine research. It is hypothesized that maladaptive remodeling of the optic nerve sheath (ONS), in response to microgravity-induced elevations in intracranial pressure (ICP), contributes to VIIP. However, little is known about ONS biomechanics. In this study, we developed a custom mechanical testing system that allowed for unconfined lengthening, twisting, and circumferential distension of the porcine ONS during inflation and axial loading. Data were fit to a four-fiber family constitutive equation to extract material and structural parameters. Inflation testing showed a characteristic "cross-over point" in the pressure-diameter curves under different axial loads in all samples that were tested; the cross-over pressure was [Formula: see text] mmHg ([Formula: see text]). Large sample-to-sample variations were observed in the circumferential strain, while only modest variations were observed in the circumferential stress. Multiphoton microscopy revealed that the collagen fibers of the ONS were primarily oriented axially when the tissue was loaded. The existence of this cross-over behavior is expected to be neuroprotective, as it would avoid optic nerve compression during routine changes in gaze angle, so long as ICP was within the normal range. Including these observations into computational models of VIIP will help provide insight into the pathophysiology of VIIP and could help identify risk factors and potential interventions.

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.

Successful use of mitomycin C to prevent recurrence of the cystic component of an optic nerve sheath meningioma

A 28-year-old woman presented with 4 months of episodic right-eye vision loss and proptosis. Imaging demonstrated a cystic retrobulbar lesion. Lateral orbitotomy with drainage and biopsy revealed a cystic optic nerve sheath meningioma. The cyst recurred despite radiation therapy followed by craniotomy with partial resection of the meningioma. In an effort to preserve vision, an anterior orbitotomy for cyst drainage with topical mitomycin C was performed. Since this procedure, the cyst and symptoms have remained stable for 19 months. We report a case of cystic optic nerve sheath meningioma and the successful treatment of cyst recurrence with mitomycin C.

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.

Development of an orbital endoscope for use with the free electron laser

PURPOSE

To explore the feasibility of designing, constructing, and testing an orbital endoscope for use with the free electron laser (FEL).

METHODS

An experimental study with an author-designed laser delivery system through an endoscope was conducted. Two adult pig cadavers and 6 fresh human cadavers had orbital endoscopy performed to develop a method of optic nerve sheath fenestration (ONSF) with the FEL. Twelve orbits were used to develop the surgical procedure by comparing visualization media and surgical technique. In the first 7 trials, a different variable was changed; the procedure was then refined in the human cadaver experiments. An ONSF was performed with the FEL (6.45 microm, 30 Hz, 2 to 3 mJ, 250-microm spot size) through a glass hollow wave guide introduced through an endoscope in 4 human cadaver orbits.

RESULTS

Visualization of the orbital structures was clearest with carbon dioxide; sodium hyaluronate did not displace the fat, and saline hydrated the orbital fat. Biopsy forceps alone did not produce a dural window in the four trials that used the forceps. A dural window was made by using the FEL through a glass hollow wave guide adapted to the Olympus HYF-XP endoscope in the second, third, fifth, and sixth human trials with the FEL. Histologic evidence of the ONSF was produced.

CONCLUSIONS

A hollow wave guide capable of transmitting the FEL through an endoscope was successfully constructed. ONSF with the FEL applied through an endoscope is technically feasible. Additional studies are currently examining techniques to improve intraorbital endoscopy.

Chronic and acute analysis of optic nerve sheath fenestration with the free electron laser in monkeys

BACKGROUND AND OBJECTIVES

The Amide II wavelength (6.45 microm) produced by the free electron laser (FEL) can efficiently create an optic nerve sheath fenestration in rabbits. We wished to determine if it would be equally successful in macaque monkeys and to determine the histopathologic changes between traditional scissors or knife optic nerve sheath fenestration to FEL fenestration.

STUDY DESIGN/MATERIALS AND METHODS

Optic nerve sheath fenestration was performed using either the FEL (6.45 microm, 30 Hz, 2-3 mJ, 325-microm spot size) through a hollow waveguide probe in 12 eyes or with a scissors or a knife in 6 eyes. The monkeys survived 1 month with the fellow optic nerve operated acutely just prior to sacrifice. Optic nerves were evaluated histologically.

RESULTS

Less tissue manipulation was required using the FEL surgical probe. Electroretinograms showed minimal or no change. Tissue responses using either method were similar following chronic or acute incisions. Mild upregulation of vimentin and glial fibrillary acid protein (GFAP) was seen in astrocytes adjacent to the fenestration, but no change in S100 beta was evident.

CONCLUSIONS

The FEL energy at 6.45 microm delivered through a hollow waveguide appears capable of efficiently and safely producing an optic nerve sheath fenestration in monkeys. This innovative surgical technique should be considered for human use.