Optometry case study: Unilateral raised optic nerve head

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Figure 4. Px MRI scan

by Suchi Rathod, Specsavers Watergardens, VIC

History

Px: 27-year-old female
Reason for visit: Presented for her routine two-yearly check-up. A few mild headaches on the computer, increased in frequency over the past 6 months
GH: No health issues, no meds
POH: No ocular issues, SVD since 2014 for computer
FOH: No relevant issues

Clinical assessment

Refraction:
Vision with current Rx:
RE: 0.00/-0.50×180   6/6       LE: 0.00/-0.50×180     6/6

Subjective refraction (with binocular balance):
RE: 0.00/-0.50×180   6/6       LE: +1.25/-0.50×180    6/6

Fundus examination:
RE: Healthy disc and macula (Figure 1)
LE: Mild hyperaemic optic nerve with blurred margins; chorioretinal folds emanating from the optic disc (Figure 2)

Colour vision: No errors monoc.
Ocular motility: Full but pain and diplopia on upgaze
Pupils: PERRLA, NAPD
Visual field: Within normal limits OU

Diagnosis

Differential diagnosis:

  • Optic neuritis
  • Optic nerve tumours
  • Optic nerve head drusen
  • Thyroid eye disease

Management

Given the hyperopic shift in the LE with retinal folds and a very mildly elevated optic nerve, an ophthalmic referral was arranged urgently for further investigation. Subsequently, the ophthalmologist arranged a magnetic resonance imaging (MRI) scan of the head and orbit. Relevant blood test results were all within normal limits.

MRI demonstrated circumferential fusiform retrobulbar thickening of the optic nerve sheath (see Figures 3 and 4). A diagnosis of retrobulbar optic neuritis was made by a radiologist but a second opinion from a neuro-ophthalmologist was sought as the referring ophthalmologist did not agree. A neuro-ophthalmologist diagnosed the mass as an optic nerve sheath meningioma (ONSM) based on good visual acuity and ‘tram tracking’ sign on the MRI.

Patient was then monitored with a repeat MRI, VFT and OCT in 3 months’ time. Progressive visual field loss and increase in nerve swelling on the OCT was noted. Fractionated stereotactic radiotherapy was then recommended as the only option of treatment.

Discussion

ONSMs are defined as benign neoplastic growth of meningiothelial cap cells of arachnoid villi1 which occur anywhere within the anterior visual pathway. ONSMs can be both unilateral and bilateral but only 5% of ONSM present bilaterally2.

The pathognomonic presentation of an ONSM includes a gradual reduction in vision, optic nerve atrophy and optociliary shunt vessels at the end stage of the condition3. However, only a quarter of patients will demonstrate this clinical triad of signs.

The most common presentation of an ONSM is a gradual optic neuropathy and mild proptosis2. Chorioretinal folds are rarely seen in the presentation of ONSM4 and are due to retinal layers being placed under physical stress such as with inflammation of the orbit and even with hyperopic shifts as a result of deformation of the globe. In this case, the ophthalmologist noted a marked increased in IOP on upgaze (from 12mmHg to 26mmHg) due to the compressive nature of the tumour.

This case is an example of a patient with an ONSM found only through ophthalmoscopy and highlights the importance of neuroimaging as she was asymptomatic. There was also an absence of any visual field defects and colour vision loss which are typical of optic tumours, neuritis and atrophy. This makes differentiating the causes of a unilateral raised optic disc difficult without radiological investigation and should prompt practitioners to refer for diagnostic imaging. Optometrists should also be aware that while chorioretinal folds are not a common presentation of ONSM, it is important to be familiar with their appearance as patients may be under surveillance if vision is uncompromised in the earlier stages of ONSM.

REFERENCES

  1. Turbin RE, Pokorny K. Diagnosis and treatment of orbital optic nerve sheath meningioma. Cancer Control: Journal Of The Moffitt Cancer Center. 2004;11(5):334-41.
  2. Moster ML. Detection and treatment of optic nerve sheath meningioma. Current Neurology And Neuroscience Reports. 2005;5(5):367-75.
  3. Eddleman CS, Liu JK. Optic nerve sheath meningioma: current diagnosis and treatment. Neurosurgical Focus. 2007;23(5):E4-E.
  4. Yeung L, Lai C-C, Chen T-L, Wu W-C. Chorioretinal folds associated with a meningioma. Chang Gung Medical Journal. 2005;28(8):575-80.
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