Optic nerve sheath meningioma: causes, diagnosis, treatment

Optic nerve sheath meningioma (ONS) is a meningioma arising from the optic nerve sheaths. It grows parallel to the nerve, forming a "cuff" on the outside, and therefore disrupts its blood supply and axonal transport quite early. The clinical outcome is progressive, painless vision loss in one eye, often with moderate exophthalmos. Fundus examination initially reveals disc swelling, followed by pallor and atrophy. Some patients develop optic nerve collaterals, a classic but not essential clue. [1]

Based on their location, primary meningioma (within the orbit and/or optic canal) and secondary meningioma (when an intracranial meningioma (e.g., the sphenoid wing) extends into the nerve sheath) are distinguished. This determines the risk of compression, radiation strategy, and surgical limitations. [2]

In the vast majority of cases, diagnosis is made not by biopsy, but by a combination of clinical findings and neuroimaging. Optic nerve biopsy is almost always contraindicated: it carries a high risk of irreversible blindness and does not add critical information to a typical presentation. [3]

The main practical conclusion: today, the "gold standard" for organ-preserving treatment of symptomatic MOND is modern fractionated radiation therapy (FSRT or proton beam), not primary orbital surgery. Observation is chosen only in limited scenarios. [4]

Table 1. The Ministry of Health at a glance (key facts to get you started)

Paragraph	Short
Essence	Meningioma growing along the optic nerve sheath
Typical debut	Painless loss of vision, ± mild exophthalmos
Key symptom	Optociliary shunts (not always)
Diagnostics	MRI/CT, "tram tracks"/"donut", calcifications
First-line treatment	Fractionated conformal RT (FSRT/protons)
Surgery	Selectively (not without reason “the last argument”) [5]

Who does this happen to and where does it come from?

MOZN is a rare orbital tumor in adults, most commonly occurring in middle-aged women. It is rare in children, but when it occurs, it is significantly more often associated with neurofibromatosis type 2 (NF2) and/or other tumors of the optic pathway. This changes the prognosis, increases the risk of bilateral involvement, and necessitates a more cautious approach to radiation therapy (taking into account growth and doses to the lens and retina). [6]

At the molecular level, MOZN is a Grade 1 meningioma (more common), less commonly a Grade 2 meningioma. It is not an "intradicular" tumor (unlike a glioma): it presses on the nerve from the outside, involving the vascular and cerebrospinal fluid spaces of the meninges. Therefore, even relatively small tumors can quickly impair function. [7]

Risk factors for secondary nerve sheath lesions include adjacent intracranial meningiomas of the skull base (sphenoid wing, planum) that extend into the nerve canal. In these cases, clinical symptoms may include ophthalmoplegia, headaches, and congestive changes in the optic disc. [8]

In pediatrics, the prevalence of genetic syndromes is higher, and the natural history is more aggressive. Therefore, screening and treatment planning are conducted multidisciplinary with a neuro-oncologist and radiation oncologist, with extremely strict dose restrictions for visual structures. [9]

Table 2. MOZN in adults and children: where are the differences?

Parameter	Adults	Children
Associations	Sporadically	Often NF2, bilateral
Pace	Slow but steady	It could be faster
Starting tactics	Observation/radiation in case of progression	Screening + organ preservation, especially doses
Long-term risks of RT	Cataract, retinopathy, neuropathy	The same + impact on growth/endocrine axis (minimized) [10]

How it manifests itself and what to confuse it with

The most common complaint is a gradual, sometimes fluctuating, "clouding" of one eye. Pain is usually absent or disproportionately mild compared to the loss of vision. During biomicroscopy, the fundus may be normal in the early stages; later, disc edema appears, followed by a waxy pallor. Outside the eye, mild exophthalmos is observed, and sometimes movement is limited in the presence of large tumors. [11]

Optociliary shunt vessels are collaterals that "shift" blood into the ciliary venous system when resistance in the central retinal vein is increased. They are found in retinal occlusion, but can also be seen in chronic glaucoma, venous occlusion, chronic papilloedema, and disc drusen. So, this is a clue, not a death sentence. [12]

Differential diagnosis includes optic nerve glioma (often pediatric and NF1-associated), inflammatory neuropathy, sarcoidosis, metastases, and chronic central vein occlusion. MRI pattern, age, speed, and associated features (for example, Lisch nodules/"café-au-le" lesions in NF1 are more likely to be glioma) help differentiate these conditions. [13]

Functionally, we focus on visual acuity, visual field (often central and centrocecal scotomas), and contrast sensitivity. The better the initial parameters, the higher the chance of stabilization/improvement after radiation therapy—this is one of the most reliable predictors of response. [14]

Table 3. MOZN versus "mimicry": what tips the scales

Sign	MOZN	Glioma of the optic nerve	Chronic papilloedema/drusen
Age	30-60 years old	Childhood/Adolescence	Any
Pain	Rarely	Rarely	Rarely
Optociliary shunts	Often	Less often	Possible
MRI "tram tracks"/"donut"	Typically	No (more often "thickening of the rod")	No
Calcifications on CT	Often	Rarely	No/rarely [15]

How to Confirm the Diagnosis: Visualization and Key Signs

Orbital MRI with contrast is the primary method. MOND is characterized by ring-shaped enhancement of the sheath around the non-enhancing nerve core—"tram tracks" on axial images and a "donut" on coronal images. Sheath thickening is often visible along the course of the nerve, and when extended, in the canal and up to the chiasm. [16]

Thin-slice CT is useful for detecting calcifications within the tumor and orbital/canal wall hyperostosis, which supports the diagnosis of meningioma and helps plan radiation therapy (contours, densities, and bone contact). Calcifications are found in approximately 20-50% of meningioma cases. [17]

Functional tests complete the picture: standard visual fields, OCT of the nerve fiber layer and ganglion complex (to quantitatively monitor atrophy), and color vision tests. With typical imaging and clinical findings, biopsy is not indicated. [18]

If the clinical picture doesn't match the typical one (e.g., severe pain, rapid growth, dense nodules), we raise the suspicion for alternatives (other tumors, inflammation) and discuss advanced diagnostics. However, "diagnostic" orbitotomy for typical MOI is a path to blindness, not truth. [19]

Table 4. Visualization markers of the MOZN

Sign	What is this	Why is it important?
Tram Rails (ax)	Reinforcing shell around the rod	The most recognizable MR pattern
Donut (cor)	Ring-shaped enhancement around the nerve	Confirms the "cuff"
Calcifications (CT)	Dense inclusions in the mass	In favor of meningioma
Canal/chiasma	Proximal spread	Affects the RT plan and prognosis [20]

How do we treat it: observation, radiation, or surgery?

Observation is warranted if vision is preserved, symptoms are minimal, and MRI shows no growth. This buys time, but we must be mindful of the risk of "silent" deterioration of function: visual field/OCT/acuity monitoring is mandatory every 3-6 months during the first year, and then on a case-by-case basis. Any documented improvement in visual function or volume is a signal for active treatment. [21]

Radiation therapy (fractionated stereotactic, tomotherapy, proton therapy) is the treatment of choice for vision loss/growth. Meta- and monocentric series demonstrate high local control and preservation/improvement of vision in the majority of patients: depending on the technique, stabilization/improvement is achieved in approximately 60-85% of patients, with low rates of serious toxicity. Protons offer the additional benefit of sparing dose distribution to the lens/retina. [22]

Surgery for primary orbital meningiomas is the exception, not the rule: direct intervention on the nerve sheath almost always results in blindness. Classic reviews have shown vision improvement in only a few cases and deterioration in the majority. Surgery is appropriate for massive exophthalmos with eyelid disease/dysfunction, and for secondary tumors with an intracranial component, when the goal is decompression or removal of the "donor" meningioma, rather than the "cuff" on the nerve. [23]

Radicality is not the goal. The goal is to stop vision deterioration and save the eye. Therefore, the sequence is as follows: observation during stability → conformal RT during function/volume progression → very selective surgery for functional indications or secondary lesions. [24]

Table 5. When to choose what

Scenario	First line	Why
Good vision, stable MRI	Observation with strict monitoring	Avoiding excess toxicity
Decreasing sharpness/fields or increasing	Fractionated RT (FSRT/IMRT/protons)	Better preservation/improvement of vision
Secondary meningioma with intracranial nucleus	Combinations: neurosurgery ± RT	We remove the “donor” and irradiate the shell.
"Cosmetic" or compressive problem	Elective surgery/debulking	Function > radicality [25]

What modern data on radiation therapy shows

Fractionated RT offers a high probability of control and visual gain. Large, modern series report: visual improvement/stabilization in ~60-80% of cases, local control >90%. For proton therapy, Heidelberg and other groups demonstrate a 5-year relapse-free survival rate of ~100% and visual stability/improvement in ~84%, with an emphasis on careful dosimetry along the visual axis. [26]

Hypofractionated regimens (e.g., 25 GyE for 5 fr) are being actively studied; preliminary results demonstrate acceptable toxicity and preservation of function with strict selection and modern planning. The choice between fSLT, hypofractionation, and protons is a matter of individualization (volume, proximity to the chiasm, age, unilaterality, comorbidities). [27]

Gamma Knife and other radiosurgical platforms for MND are used only in fractionated mode or in soft single doses; data from 2025 indicate comparable efficacy to EBRT with proper fractionation and selection, but ophthalmologic risks are higher with “hard” doses. [28]

Toxicity that should be discussed in advance: radiation cataracts, retinopathy, ischemic optic neuropathy. Modern fractionation and dose limitations for the lens/retina/nerve significantly reduce the risks, but do not eliminate them. Therefore, correct timing (not too late) and high-quality planning CT/MRI are key. [29]

Table 6. Radiation therapy for MOZN - what the series say (summary)

Method	Tumor control	Vision (stabilized/improved)	Typical risks
FSRT/IMRT (fractional)	>90%	~60-70%	Cataract, retinopathy (rare)
Proton therapy	~100% (5-year LPV)	~80-85%	Same, lower doses off-target
Hypofraction 5×	Promising	Promising	Strict selection/planning is required [30]

Children, NF2 and 'too many unknowns'

In children, MONS is rare, but when it does occur, it is often associated with NF2, can be bilateral, and behave less favorably. Consensus: initiate treatment earlier at the first signs of functional progression, but minimize doses to developing structures; if possible, consider proton therapy. [31]

Radiation toxicity in children is a subject of special monitoring: the lens, macula, and orbital bone growth. Modern proton plans allow for a significant reduction in the integral dose, as confirmed by pediatric series on meningiomas in general. However, platform selection is not automatic, but rather physical and dosimetric (we collate plan-to-plan). [32]

In NF2, there are often "competing priorities" (vestibular schwannomas, basal meningiomas). Therefore, the plan is developed by the team at the Rare Tumor Center: ophthalmology, radiation oncology, neurosurgery, and genetics. The goal is maximum vision preservation with minimal late complications. [33]

Surgical interventions in children with MOND are considered even more cautiously than in adults. Exceptions include a massive secondary component or "non-ophthalmic" goals (decompression), when preserving vision is no longer possible. [34]

Table 7. Children's MOZN: practical emphases

Step	What are we doing?	Why
We confirm the typicality	MRI/CT with canal/chiasm targeting	Millimeters matter
Early team call	Ophthalmologist + radiation oncologist + neurosurgeon	Lots of ties and tight spots
We are planning LT	Preference - fractions/protons, strict dose restrictions	Reducing the risk of late effects
We follow more often	Fields/acuity/OCT every 2-3 months in the first year	The window is narrow, the cost of error is high [35]

Monitoring, outcomes, errors

After diagnosis (even during observation), a rhythm is required: visual acuity, visual fields, contrast sensitivity, and OCT of the nerve fiber layer. During the first year, every 3-6 months, then according to the dynamics. MRI - every 6-12 months or when symptoms change; after RT - according to a local protocol (often 6, 12, 24 months, then annually). [36]

What are the realistic outcomes? With modern irradiation, vision stabilization or improvement is expected in most patients, especially if treated before deep atrophy and with good initial results. Delaying therapy reduces the window of reversibility: OCT atrophy and deep field defects predict a lower chance of visual gain. [37]

Common mistakes include delaying treatment when functional progression is evident; referring for a "diagnostic" biopsy/orbitotomy; choosing single-fraction radiosurgery with high single doses to the visual axis; and underestimating secondary intracranial spread. Each of these increases the risk of irreversible blindness. [38]

It's important to explain to the patient that RT is not a "last resort," but rather a primary organ-preserving method with a good chance of halting deterioration. And secondly, success is higher when vision is still intact. This is an honest yet reassuring conversation. [39]

Table 8. Red flags and what to do immediately

Signal	Action now
New/accelerated drop in sharpness/fields	Unscheduled visit, MRI, discussion of RT
Tumor growth on MRI	RT plan (with dosimetry for the lens/retina/nerve)
Pain, atypical dynamics	Exclude alternatives/combinations, reconsider the diagnosis
Bilateral changes in a child	Search for NF2, multidisciplinary consultation [40]

What was wrong with the “classical” paradigm and what the modern one replaced it with

Historically, orbital surgery was viewed as a "fix and cure" option. However, experience has shown that vision improvement after cuff removal is extremely rare, and blindness is common. Modern reviews of postoperative outcomes confirm this: improvement occurs in a few percent of cases, while deterioration occurs in the majority. Therefore, surgery has been relegated to the periphery of the algorithm. [41]

Conformal fractionated RT (including protons) has replaced it. In different cohorts, it provides local control rates of >90% and vision stabilization/improvement in approximately 2/3-4/5 patients—especially with good baseline vision and targeted planning. This represents a paradigm shift in favor of organ preservation. [42]

Single-dose high-dose radiosurgery near the optic nerve is risky; in cases of MONS, fractionated dose delivery (including on Gamma Knife/CK platforms) or classical FSRT/IMRT/protons are appropriate. Emphasis is placed on dose limitations for visual structures. [43]

Finally, the "wait until complete atrophy and then irradiate" approach is a mistake: the sooner the treatment, the higher the chance of preserving function. This is confirmed by both retrospective and prospective observations of the relationship between RT outcome and initial vision. [44]

Table 9. "Old" versus "New" - What is the Essence of Progress?

Yesterday	Today
Biopsy/orbitotomy "for clarification"	Diagnosis by MRI/CT and clinical examination, without biopsy
Surgery as a first line	Fractionated RT as a standard for organ preservation
Single-focus radiosurgery	Fractionation/proton, strict dose restrictions
Wait until deep atrophy	Treat at the first reliable signs of progression [45]

What course of action will I propose to the patient and the doctor?

First, confirm the typicality of the image (MRI of the orbits with contrast; if in doubt, thin-film CT for calcifications). Second, establish a "zero" of functions: acuity, fields, OCT. Third, if there is documented functional or volumetric progression, discuss fractionated RT (FSRT/IMRT/protons) in a center with experience in orbital targets. [46]

The RT plan should clearly limit the doses to the lens, macula, optic nerve, and chiasm; if a proton option is available, it is reasonable to compare plans (photon vs. proton) head-to-head - sometimes this significantly reduces the integral load on the eye and brain. [47]

If initial vision is good and the tumor is stable, observation is acceptable, but with a schedule (functions every 3-6 months, MRI every 6-12 months) and a pre-agreed threshold for starting treatment (decrease in visual acuity/fields, confirmed growth). This is fair and reduces anxiety. [48]

Surgery is only recommended for strict indications (secondary intracranial lesion, severe compression/pain, reconstructive needs). In cases of one-eyedness and severe progression, the decision is particularly individualized; it is best discussed in a consultation with the patient. [49]

Table 10. Mini-protocol for the management of MOZN (adult patient)

Stage	What are we doing?	Term
Basic verification	MRI of the orbits with contrast ± CT	Now
Initial functions	Visual acuity, fields, OCT RNFL/GCIPL	Now
If progression	Fractionated RT plan (FSRT/IMRT/protons)	Within weeks
If stability	Observation: functions 3-6 months, MRI 6-12 months	According to schedule [50]