From the Department of Ophthalmology, Kim’s Eye Hospital, Konyang University College of Medicine, Seoul, Korea.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Ungsoo Samuel Kim, MD, Department of Ophthalmology, Kim’s Eye Hospital, Konyang University College of Medicine, Youngdeungpo 4th 156, Youngdeungpo-gu, Seoul, 150-034 Korea. E-mail: email@example.com
Optic nerve sheath meningocele is a primary cerebrospinal fluid (CSF) cyst of the optic nerve sheath. Although there are no known pathognomonic symptoms suggestive of an optic nerve sheath meningocele, visual blurring and headache are the two main symptoms of the condition, along with proptosis and optic disc shunt vessels as rare presenting features.1 The associated conditions reported thus far include type I neurofibromatosis, acquired hypermetropia, and choroidal folds. In the current study, we describe a patient with unilateral optic nerve sheath meningocele who presented with amblyopia with no association with type I neurofibromatosis.
An 8-year-old boy presented with a visual disturbance coupled to a 2-year history of amblyopia in the right eye. He was treated with occlusion therapy under suspicion of anisometropic amblyopia. The best-corrected visual acuity was 0.5 in the right eye and 1.0 in the left eye. The refractive errors were −1.50 diopters in the right eye and −0.75 diopters in the left eye. Subtle afferent pupillary defect was detected in the right eye and the Ishihara color test revealed total dyschromatopsia. Humphrey visual field analysis revealed an enlarged blind spot in the right eye. Fundus photography showed a slightly temporal pallor. Systemic examination revealed no specific cutaneous or neurologic abnormalities suggestive of type I neurofibromatosis. The patient’s family history was unremarkable. A magnetic resonance imaging (MRI) scan with fat-suppression and an offaxis coronal view was conducted. On the coronal images, a dilated optic nerve sheath on the right side was identified, which harbored a CSF-intensity lesion exhibiting hyperintensity on the T2-weighted images (Figure). The optic nerves were normal and no evidence of a tumor in the brain or orbit was noted.
Figure. T2-weighted magnetic resonance imaging demonstrated a hyperintense fluid-filled dilated optic nerve sheath on the right eye: (A) coronal view and (B) axial view.
Optic nerve sheath meningocele, also referred to as dural ectasia of the optic nerve sheath, is a condition characterized by dilation of the optic nerve sheath and expansion of the CSF-filled space surrounding the optic nerve. The term “optic nerve sheath meningocele” was first coined by Garrity et al.,1 who described a total of 13 patients with this condition. The first report of this entity was published by Bane in 1918,2 describing the condition as a primary cyst of the optic nerve sheath. Since that time, this entity has been reported variously as optic hydrops, ascites of the optic nerve, patulous subarachnoid space, cystic hygroma, arachnoid cyst, and perioptic subdural hygroma. Thus far, more than 30 cases have been chronicled in the English literature.2
The most common presenting symptoms in this condition were headache, visual deficits, and blurred vision. Bilateral involvement was more common than unilateral involvement; however, our case evidenced unilateral involvement. Examination may also reveal visual field deficits, pale disc or papilledema, proptosis, or optic disc shunt vessels. A subset of patients also presented with hyperopia associated with choroidal folds. Thus, some authors have divided this entity into two subgroups: one with progressive hyperopia and choroidal folds and another without. Our case featured a more profound myopic refractive error in the involved eye and no choroidal fold. This is probably because the patient was young and the tumor was not sufficiently large to push the eyeball. In some patients, this condition has been associated with neurofibromatosis type I, and these patients were generally assumed initially to harbor an optic nerve glioma rather than an optic nerve sheath meningocele.3
The diagnosis of optic nerve sheath meningocele can be confirmed by MRI with high spatial resolution, fat-suppression with contrast technique in offaxis sagittal views. On coronal MRI, it is possible to visualize both the optic nerve and sheath: an optic nerve sheath meningocele appears as a moderately dilated sheath with fluid and a normal or thickened optic nerve (“bull’s eye”). MRI also allows for a more detailed differential diagnosis of optic nerve meningocele, including optic nerve tumors, such as gliomas or meningiomas; this is particularly true in the cystic subtype of these tumors.4
The natural history of this condition has yet to be thoroughly elucidated; thus, prognostications regarding the condition are somewhat difficult. However, according to the available evidence, patients with hyperopia and choroidal folds tend to follow a more benign course.5 Suggested management guidelines include a thorough ophthalmic examination with refraction, visual fields, and axial length measurements. Surgical decompression may be considered in some reserved cases with progressive visual loss. There is also some evidence to suggest that, in some cases, this may improve vision or halt the progression of the disease.1
Optic nerve sheath meningocele remains a rare condition with a relative paucity of cases reported in the literature thus far. Its etiology, prognosis, and optimal treatment modality remain largely unknown.
- Garrity JA, Trautmann JC, Bartley GB, et al. Optic nerve sheath meningoceles: clinical and radiographic features in 13 cases with a review of the literature. Ophthalmology. 1990;97:1519–1531.
- Lunardi P, Farah JO, Ruggeri A, Nardacci B, Ferrante L, Puzzilli F. Surgically verified case of optic sheath nerve meningocele: case report with review of the literature. Neurosurg Rev. 1997;20:201–205. doi:10.1007/BF01105565 [CrossRef]
- Doi J, Uchino A, Kato A, Koga T, Kudo S. Dural ectasia of the optic nerve sheath in neurofibromatosis type 1: MRI manifestations. Radiat Med. 1997;15:197–198.
- Mesa-Gutierrez JC, Quinones SM, Ginebreda JA. Optic nerve sheath meningocele. Clin Ophthalmol. 2008;2:661–668. doi:10.2147/OPTH.S2689 [CrossRef]
- Shanmuganathan V, Leatherbarrow B, Ansons A, Laitt R. Bilateral idopathic optic nerve sheath meningocele associated with unilateral transient cystoid macular oedema. Eye (Lond). 2002;16:800–802.