1. Optic Nerve Sheath Meningiomas
Robert Egan MD
Casey Eye Institute
Department of Ophthalmology, Neurology, and Neurosurgery
Oregon Health & Science University
Portland, Oregon
November 4th, 2006

2. Optic Nerve Sheath Meningiomas
Optic nerve sheath meningiomas (ONSM) are separated into two types: primary and secondary
The primary variety arises from the cap cells of the intraorbital or intracanalicular optic nerve sheath while the secondary form arises intracranially in the region of the sphenoid wing, tuberculum sella, or olfactory groove

3. Primary ONSM Average age of onset in the 5th decade of life
Associated with painless and slowly progressive vision loss
Minimal proptosis, if any
Optociliary shunt veins may be present on the optic disc
Neuroimaging is the mainstay for diagnosis in a typical case
Radiation is treatment of choice in an eye that is having documented progressive vision loss

4. Secondary ONSM
Painless and slowly progressive vision loss with or without diplopia
Sphenoid wing meningiomas may be associated with significant disfiguring proptosis
Optociliary shunt veins are not associated with this disorder, but optic atrophy or papilledema may be present if direct tumor compression of the optic nerve or increased intracranial pressure has resulted
Neuroimaging is the mainstay for diagnosis in a typical case
Treatment consists of surgical resection with or without radiation therapy; it is reasonable to follow these patients clinically until symptoms worsen

5. Primary ONSM Average age of onset in the 5th decade of life
Associated with painless and slowly progressive vision loss
Minimal proptosis, if any
Optociliary shunt veins may be present on the optic disc
Neuroimaging is the mainstay for diagnosis in a typical case
Radiation is treatment of choice in an eye that is having documented progressive vision loss

6. Primary ONSM
The average age of onset of symptoms from these tumors is in the 5th decade of life although they may be found at any age
Some patients may even present in their 7th decade of life
ONSM account for less than 1% of all meningiomas and for only 3 to 14% of orbital tumors
Men are affected much less frequently than women and prevalence rates are recorded from 7.1% to 37.5%
These tumors may occur more frequently in the setting of neurofibromatosis type 2 and may be bilateral
Bilateral tumors, albeit rare, tend to present at an earlier age

7. Primary ONSM Average age of onset in the 5th decade of life
Associated with painless and slowly progressive vision loss
Minimal proptosis, if any
Optociliary shunt veins may be present on the optic disc
Neuroimaging is the mainstay for diagnosis in a typical case
Radiation is treatment of choice in an eye that is having documented progressive vision loss

8. Primary ONSM
Most patients with ONSM complain of reduced or blurred vision in one eye
There often is little if any proptosis
Visual acuity at presentation may be 20/40 or better in half of patients and less than 25% are count fingers acuity or worse
Roughly 50% present with disc edema; the other half with pallor
Visual fields typically show central and paracentral scotomata as well as altitudinal defects and these progress over time
Despite the typical progression of reduction in visual function, some patients maintain stable acuity for years or actually improve and this may occur in up to 30%

9. Primary ONSM Average age of onset in the 5th decade of life
Associated with painless and slowly progressive vision loss
Minimal proptosis, if any
Optociliary shunt veins may be present on the optic disc
Neuroimaging is the mainstay for diagnosis in a typical case
Radiation is treatment of choice in an eye that is having documented progressive vision loss

10. Primary ONSM
A few patients will show choroidal folds due to compression behind the globe
Optociliary shunt vein collaterals in the presence of vision loss and optic disc pallor should suggest the diagnosis of an ONSM
However, shunt veins are uncommon at presentation, but become apparent in over 1/3 of patients over a 6 year period

11. Primary ONSM Average age of onset in the 5th decade of life
Associated with painless and slowly progressive vision loss
Minimal proptosis, if any
Optociliary shunt veins may be present on the optic disc
Neuroimaging is the mainstay for diagnosis in a typical case
Radiation is treatment of choice in an eye that is having documented progressive vision loss

12. Primary ONSM
ONSMs are most easily visualized by CT or MRI as a fusiform enlargement of the optic nerve/sheath complex
There may also be flattening of the posterior globe due to tumor encroachment and the optic canal may be enlarged
ONSMs tend to calcify over time; on CT, there may be circumferential calcification and bright signal or enhancement that resembles railroad tracks on axial sections and a double ring on coronal sections
ONSMs are hypointense on both T1‑ and T2‑weighted MR images and typically enhance well after administration of gadolinium
Rarely, the ONSM may appear cystic

13. Primary ONSM
Care should be taken to make the presumptive diagnosis of an ONSM in a patient with a history of breast carcinoma
Occasionally, metastases from breast may mimic an ONSM and be misdiagnosed radiologically
Therefore, a biopsy should be undertaken in the patient with an “ONSM” and breast CA
Arachnoid cysts of the optic nerve and sarcoidosis may rarely mimic an ONSM

14. Primary ONSM Average age of onset in the 5th decade of life
Associated with painless and slowly progressive vision loss
Minimal proptosis, if any
Optociliary shunt veins may be present on the optic disc
Neuroimaging is the mainstay for diagnosis in a typical case
Radiation is treatment of choice in an eye that is having documented progressive vision loss

15. Primary ONSM
Left alone, unilateral ONSMs slowly but inexorably progress to produce blindness of the involved eye
However, this is not always the case
Some patients maintain stable vision for years or even enjoy mild improvement
Intraorbital and intracanalicular meningiomas extend intracranially only rarely and are not associated with any mortality
In contrast, tumors that begin intracranially often extend to involve the chiasm and other structures adjacent to the optic nerve and may lead to blindness of the other eye

16. Primary ONSM
Surgical removal is not indicated due to the high likelihood of inducing blindness
This is caused by the unavoidable dissection of the pial vascular supply of the optic nerve
This option may be considered in an eye that is already blind

17. Primary ONSM
Recently, several series have been published documenting treatment outcomes with 3 dimensional conformal radiation therapy (3D-CRT) or stereotactic fractionated radiotherapy
In total, these reports indicate that some patients will have improvements in acuity, but more commonly enjoy improvement in visual field
A greater number of patients develop stability in their visual acuity and visual fields while only a small number worsen
Cilioretinal shunt veins may regress as the tumor shrinks

18. Primary ONSM
Risks of radiation therapy are not well understood at this time as only a few small sized treatment studies have been published with limited follow up
There are several reports of radiation retinopathy as well as iritis, dry eye, or orbital pain
Since these tumors are uncommon, it remains likely that the true prevalence of complications will only be inferred through case reports and other small series
Complication rates may decrease with greater application of 3D conformal techniques

19. Primary ONSM
Since some patients may not progress for years, close follow up is recommended
The routine application of radiation therapy may unnecessarily expose some patients to complications and should be reserved for those patients whose visual function declines under close observation
Therefore, since the long term risks of radiation treatment are still not fully known and these tumors only cause blindness without other morbidity or mortality, observation should remain part of the treatment armamentarium and discussed with each patient

20. Susac Syndrome