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Editor,

We wish to report the case of a 31-year-old woman who presented with a 1-month history of distortion of vision in her left eye. She had a past history of right strabismus amblyopia. Examination showed best corrected visual acuity of 6/18 and 6/6 in the right and left eyes, respectively. Humphrey's visual field analysis revealed an enlarged blind spot. Dilated funduscopy showed an elevation of the left optic disc.

A B-scan was performed to exclude optic disc drusen and a ‘cyst’ was identified behind the left optic disc, which was further confirmed with optical coherence tomography (OCT), as shown in Fig. 1.

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Figure 1. OCT scan through optic disk.

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A magnetic resonance imaging (MRI) scan with fat-suppression and off-axis sagittal view was performed (Figs. 2 and 3). On orbital axial images, a dilated optic nerve sheath was identified as containing a Cerebrospiral Fluid (CSF)-intensity lesion that was hyperintense on T2-weighted images. The optic nerves were normal and there was no evidence of tumour in the brain and orbit. The subject was, therefore, diagnosed as having dural ectasia of the optic nerve sheath, which is also known as optic nerve meningocoele.

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Figure 2. Sagittal view of T2-weighted MRI scan.

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Figure 3. Coronal view of T2-weighted MRI demonstrated a fluid-filled dilated sheath surrounding normal optic nerves. An appearance sometimes referred to as “Bull's Eye”

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Once the diagnosis had been confirmed and the neurosurgical team consulted, the decision to observe the subject was made. She remained stable over the next 15 months.

There were no pathognomonic symptoms that may lead one to suspect an optic nerve dural ectasia. Garrity et al. (1990) reported visual blurring and headache as two main symptoms, along with proptosis and optic disc shunt vessels as rare presenting features.

An optic nerve meningocoele may be suspected in a young patient with the symptoms described above and can be demonstrated by B-scan or OCT. The diagnosis can be confirmed by MRI with high spatial resolution, fat-suppression with contrast techniques in off-axis sagittal views.

Apart from its relation with neurofibromatosis type 1 (Lovblad et al. 1994; Doi et al. 1997), dural ectasia of the optic nerve sheath has been associated with acquired hypermetropia and choroidal folds (Dailey et al. 1986; Garrity et al. 1990). The clinical features of these patients were reported by Dailey et al. (1986) and (Garrity et al. (1990). Most of their patients followed a benign clinical course. The role of corticosteroid is not described in the literature; however, in view of its presumed pathology, it may not be beneficial. Surgical intervention involving optic nerve sheath fenestration could be reserved for patients with progressive optic nerve dysfunction.

In summary, optic nerve dural ectasia is a saccular dilatation of the optic nerve sheath. It can be suspected based on the evidence of visual blurring or retrobulbar pressure. Ocular examination may show signs of optic nerve dysfunction. Choroidal folds and hypermetropic shift are suggestive of a meningocoele. The radiological investigation of choice is MRI with techniques to emphasize high spatial resolution and optic nerve anatomy. Surgical intervention is reserved for severe cases of optic nerve decompression.

References

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  2. References
  • Dailey RA, Mills RP, Sticmac GK et al. (1986): The natural history and CT appearance of acquired hyperopia with choroidal folds. Ophthalmology 93: 13361342.
  • Doi J, Uchino A, Kato A et al. (1997): Dural ectasia of the optic nerve sheath in neurofibromatosis type 1: MRI manifestations. Radiation Med 15: 197198.
  • Garrity JAMD, Trautmann JC, Bartley GB et al. (1990): Optic nerve sheath meningocoele. Ophthalmology 97: 15191153.
  • Lovblad KO, Remonda L, Ozdoba C et al. (1994): Dural ectasia of the optic nerve sheath in neurofibromatosis type 1: CT and MR features. J Comput Assist Tomogr 18: 728730.