Dilation of the Perioptic Subarachnoid Space Anterior to Optic Nerve Sheath Meningioma

Photo Essay Section Editors: Melissa W. Ko, MD Dean M. Cestari, MD Peter Quiros, MD Dilation of the Perioptic Subarachnoid Space Anterior to Optic Nerve Sheath Meningioma Anthony C. Arnold, MD, Andrew G. Lee, MD Downloaded from http://journals.lww.com/jneuro-ophthalmology by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdtwnfKZBYtws= on 05/04/2022 FIG. 1. Color fundus photographs. Initial evaluation. Right eye (top left) showing optic disc edema without retinochoroidal collateral vessels. Left eye (top right) showing normal optic disc. Follow-up evaluation 4 years later. Right eye (bottom left) continues to show optic disc edema without retinochoroidal collateral vessels. Left eye (bottom right), optic disc remains normal. T umors that compress the retrobulbar optic nerve at a position posterior to the exit of the central retinal vein (CRV) from the optic nerve sheath typically produce Department of Ophthalmology (ACA), Stein Eye Institute, University of California, Los Angeles; Department of Ophthalmology (AGL), Houston Methodist Hospital, Houston, Texas; Baylor College of Medicine (AGL), The Baylor Center for Space Medicine, Houston, Texas; Departments of Ophthalmology, Neurology, and Neurosurgery (AGL), Weill Cornell Medical College, New York, New York; Department of Ophthalmology (AGL), The University of Texas Medical Branch, Galveston, Texas; Department of Ophthalmology (AGL), The University of Iowa Hospitals and Clinics, Iowa City, Iowa; and The UT MD Anderson Cancer Center (AGL), Houston, Texas. The authors report no conflicts of interest. Address correspondence to Anthony C. Arnold, MD, UCLA Stein Eye Institute, 100 Stein Plaza, Los Angeles, CA 90095; E-mail: [e-mail] e100 progressive optic atrophy without optic disc edema, whereas those anterior to the CRV exit often result in optic disc edema, presumably due to compromised venous outflow with resultant optic disc congestion. There is evidence, however, that more posterior optic nerve compressive tumors may be associated with dilation of the perioptic subarachnoid space (SAS) anterior to the lesion, and chronic optic disc edema may be present. Our report demonstrates long-term clinical and radiographic follow-up of a patient with dilated perioptic SAS and chronic optic disc edema secondary to a presumed optic nerve sheath meningioma. A 54-year-old woman was noted to have optic disc edema in the right eye on routine examination. She reported vague intermittent visual blurring, but the visual acuity and automated perimetry were normal. Over the next Arnold and Lee: J Neuro-Ophthalmol 2021; 41: e100-e102 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay FIG. 2. MRI of the orbits. Axial orbital views. T1-weighted image (top left) with fat-suppression and gadolinium administration: The right optic nerve sheath is thickened and enhancing from the optic canal to mid-orbit. A sharp demarcation is present at mid-orbit, anterior to which the perioptic subarachnoid space is dilated to the globe. Axial T2-weighted image (top right) confirms dilation of the subarachnoid space anteriorly on the right with no space visible posteriorly. Coronal orbital views. T1-weighted image through mid-posterior orbit (bottom left) shows thickened and enhancing right optic nerve sheath. T2-weighted image through anterior orbit (bottom right) shows dilated perioptic subarachnoid space on the right. 2 months, she developed transient visual obscurations with blackout of vision in the right eye lasting seconds, associated with orthostatic change or rapid head movements. The past medical, surgical, family, allergic, and medication histories were noncontributory. Examination revealed visual acuity of 20/20 in each eye with normal color vision and pupillary responses. The right optic disc showed 1+ edema, without optic atrophy or retinochoroidal venous collateral vessels (Fig. 1). The remainder of the examination was normal. Perimetry was normal. MRI of the orbits revealed thickening and enhancement of the right optic nerve sheath in the posterior orbit and optic canal, consistent with optic nerve sheath meningioma. The perioptic SAS anterior to the tumor was dilated, with increased T2 weighted hyperintensity consistent with cerebrospinal fluid (CSF), with a sharp demarcation at the anterior tumor margin, 12 mm posterior to the globe (Fig. 2). Conservative management with observation was recommended, and the symptoms decreased without visual loss. Two years later, transient visual obscurations in the right eye recurred with increased frequency. Examination again revealed visual acuities of 20/20, with normal pupillary reactions, mild optic disc edema right eye, and otherwise normal findings. Automated perimetry demonstrated mild blind spot enlargement. MRI showed no significant change in the lesion. Arnold and Lee: J Neuro-Ophthalmol 2021; 41: e100-e102 The patient preferred to defer treatment, with continuing mild transient visual obscurations in the right eye but no persistent visual loss or other symptoms. Two years later, she again reported increasing visual symptoms and was reevaluated. Visual acuities remained 20/20 with normal color vision, pupillary reactions, and mildly increased optic disc edema (Fig. 1). MRI, however, remained unchanged, with evidence of perioptic SAS distention and increased CSF collection anterior to the lesion. McNab and Wright (1) described cystic enlargement of the optic nerve sheath in 3 cases of intraorbital meningioma. In one of the cases, optic disc edema was present; at exploratory surgery, the dilated perineural optic nerve space was incised, with emergence of a gush of fluid suggesting high pressure within the perioptic SAS. Lindblom et al. (2) reported 7 cases of focally dilated perioptic SAS anterior to optic nerve sheath meningiomas; 3 of the 7 had chronic optic disc edema, although no other details of the clinical examination were described. Imaging in the 3 cases shown demonstrated posterior orbital tumors with varying anterior extent, all with the sharp demarcation of the tumor from anterior dilated perioptic SAS, as seen in our case. The anterior border of the tumors ranged from 6 to 10 mm posterior to the globe. Killer et al. (4) also described unilateral disc edema secondary to an orbital apex meningioma, anterior to which the perioptic SAS was distended. e101 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay The mechanism by which the perioptic SAS becomes dilated and its relation to optic disc edema remains unclear. Killer et al. (3) postulated that even in the absence of mechanical tumor blockage of flow around the optic nerve, the perioptic SAS is trabeculated and may be compartmentalized and separate from the remainder of the space in the central nervous system. Decrease of the venous and lymphatic outflow may result in increased pressure and possibly collection of toxins, both contributing to optic disc edema in the absence of elevated intracranial pressure elsewhere. Mader et al. (4) have recently reported on unilateral and asymmetric optic disc edema developing in space travel, again raising the issue of compartmentalization within the perioptic SAS, impaired venous and lymphatic (glymphatic) outflow, at least partially the result of the low-gravity environment. Our case suggests that chronic unilateral optic disc edema may result from dilation of the perioptic SAS anterior to a posterior optic nerve sheath meningioma that does not directly compress the central retinal vein as it traverses the space. Whether the optic disc edema results from locally increased SAS pressure, collection of e102 toxins, or both, remains unproven. Although dilation of the perioptic SAS (with increased T2 weighted MRI CSF signal) is a typical radiographic feature of increased intracranial pressure, any compressive lesion in the orbit may reduce CSF egress from the perioptic SAS and produce dilation. The dilated SAS, especially if unilateral, should prompt detailed orbital imaging with gadolinium administration and fat suppression to detect an occult compressive lesion. REFERENCES 1. McNab AA, Wright JE. Cysts of the optic nerve. Three cases associated with meningioma. Eye 1989;3:355–359. 2. Lindblom B, Norman D, Hoyt WF. Perioptic cyst distal to optic nerve sheath meningioma: MR demonstration. AJNR 1992;13:1622–1624. 3. Killer HE, Jaggi GP, Flammer J, Miller NR, Huber AR. The optic nerve: a new window into cerebrospinal fluid composition. Brain 2006;129:1027–1030. 4. Mader TH, Gibson OD, Otto CA, Sargsyan AE, Miller NR, Subramanian PS, Hart SF, Lipsky W, Patel NB, Lee AG. Persistent asymmetric optic disc swelling after long-duration space flight: implications for pathogenesis. J Neuroophthalmol 2017;37:133–139. Arnold and Lee: J Neuro-Ophthalmol 2021; 41: e100-e102 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.