Optic Nerve Sheath Meningioma

Key Points at a Glance

Key Points of This Disease

• Optic nerve sheath meningioma (ONSM) is a benign tumor originating from the arachnoid granulations of the optic nerve sheath, causing slowly progressive, painless, unilateral vision loss over years.
• It accounts for approximately 1-2% of all meningiomas and about 10% of all orbital tumors, and is more common in women in their 40s-50s (female:male = 3:1).
• The tram-track sign on MRI is a characteristic imaging finding, and in typical cases, biopsy is unnecessary and nearly contraindicated.
• The classic triad of optic atrophy, retinochoroidal collateral vessels (RCVC), and painless vision loss (Hoyt-Spencer sign) is known, but only a minority of cases present with all three.
• When intervention is needed, the first choice is radiation therapy (IMRT or stereotactic radiotherapy), which can stabilize or improve vision and visual fields.
• Surgical resection is generally not recommended when useful vision remains, due to the high risk of vision deterioration.
• In pediatric cases, up to 35% are associated with NF2, and the risk of intracranial extension is higher, requiring different management than in adults.

1. What is Optic Nerve Sheath Meningioma?

Optic nerve sheath meningioma (ONSM) is a benign tumor arising from meningothelial cells of the arachnoid granulations of the optic nerve sheath. It occurs where the meningeal sheath exists within the orbit or optic canal, growing concentrically around the optic nerve. It is important to distinguish between “secondary” ONSM, where an intracranial meningioma extends anteriorly to the optic canal, and “primary” ONSM, which originates from the optic nerve sheath.

Epidemiology: ONSM accounts for approximately 1-2% of all meningiomas, about 10% of all orbital tumors, and about 33% of primary optic nerve tumors. It predominantly affects adult women in their 40s-50s (with peaks in the 30s and 60s), with a female-to-male ratio of 3:1. In children, it is rare (<4% of all cases), but up to 35% of pediatric cases are associated with neurofibromatosis type 2 (NF2). ⁴⁾

Q Is optic nerve sheath meningioma malignant?

A

Histologically, most are benign (WHO Grade 1), but some reports indicate that about 20% show malignant features. Rarely, they may exhibit malignant or invasive characteristics with higher recurrence rates. In children, the potential for malignancy is higher than in adults, and the risk of intracranial extension is also greater.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

• Slowly progressive vision loss: The most common symptom is painless, unilateral vision loss. It typically follows a chronic course over years. At initial presentation, visual acuity ranges widely from 20/20 to no light perception (NLP). In Dutton’s review, 24% had counting fingers or worse, and 45% had 20/40 or better.
• Visual field defects: Patchy sensitivity loss or concentric visual field defects. Visual acuity is often mildly impaired, but can be severely impaired if a central scotoma is present.
• Blurred vision / subacute visual deterioration: Blurred vision or subacute worsening of visual field and acuity may occur during the course.
• Proptosis: Mild proptosis may be present.
• Ocular motility disturbance: Mild restriction of eye movement may occur.

Clinical Findings

The following three are known as the classic triad (Hoyt-Spencer sign). However, only a minority of cases present with all three.

1. Painless, slowly progressive visual loss
2. Optic atrophy (pale optic disc)
3. Opticociliary shunt vessels (retinochoroidal venous collaterals, RCVC)

Other findings are listed below.

• RCVC (retinochoroidal venous collaterals): Reported in approximately 20–60% of cases, with variability among reports. These are not true shunts but collateral vessels formed in response to chronic central vein obstruction (blood flow from retinal to choroidal circulation). They cross the optic disc margin, appear large in caliber, and show no dye leakage on fluorescein angiography. ³⁾
• Positive RAPD: Relative afferent pupillary defect is positive.
• Color vision loss: Color vision loss occurs due to optic nerve compression.
• Temporal changes in fundus findings:
  • Early stage: Mild to localized optic disc hyperemia and swelling
  • Advanced stage: peripapillary retinal edema and retinal folds
  • Chronic phase: progression from pale edema to optic atrophy (irreversible visual impairment)
• Optical coherence tomography (OCT): Useful for evaluating optic disc swelling and quantifying thinning of the retinal ganglion cell complex (GCC). Advanced cases show marked thinning (reported examples: retinal nerve fiber layer 50 μm/49 μm, normal 100–120 μm; GCL <60 μm, normal >80 μm). ⁴⁾

Q What are the abnormal blood vessels seen around the optic disc?

A

These are collateral vessels called retinociliary shunt vessels (RCVC), which are compensatory vascular formations in response to chronic compression of the central retinal vein by the tumor. They are not true shunts and are not specific to ONSM (also occur in CRVO, chronic papilledema, etc.). Known as one of the classic triad, they are found in approximately 20–60% of ONSM cases.

3. Causes and Risk Factors

Most cases are idiopathic with no clear cause. The following risk factors and associated conditions are known.

• Exposure to ionizing radiation: Associated with meningiomas in general.
• NF2 (Neurofibromatosis type 2): The most common genetic abnormality is deletion of the long arm of chromosome 22 (including the NF2 gene region). The rate of ONSM in NF2 patients is reported to be approximately 6.8%, and up to 35% of pediatric ONSM patients have NF2. ⁴⁾
• Special features in children: Higher potential for malignancy and higher rate of intracranial extension compared to adults. Complication rates after radiotherapy are also higher.
• Obesity, hormone replacement therapy, breast cancer, and alcohol have been reported as risk factors for meningioma in general, but evidence as specific risk factors for ONSM is limited.

Regular Eye Examinations

Optic nerve sheath meningioma progresses slowly, so there may be a long asymptomatic period and delayed diagnosis. Especially if you have been diagnosed with NF2 or have chronic vision loss or visual field abnormalities in one eye, please consult an ophthalmologist or neuro-ophthalmologist early.

4. Diagnosis and Examination Methods

Imaging Diagnosis

MRI (first choice): Gadolinium-enhanced fat-suppressed head and orbital MRI is most useful. Fat-suppressed T1-weighted contrast-enhanced images are considered particularly important.

• Tram-track sign: On axial sections, the tumor appears as two linear hyperintense shadows on both sides of the hypointense optic nerve.
• Doughnut sign: On coronal sections, the tumor surrounds the central optic nerve in a ring-like pattern. ⁵⁾
• T1-weighted images: Slightly hypointense relative to extraocular muscles.
• T2-weighted images: Approximately isointense to fat, hypointense relative to vitreous (differentiating from optic nerve glioma).
• Post-contrast: Homogeneous and strong enhancement.
• Also essential for evaluating intracranial extension.

CT:

• Diffuse tubular lesion with contrast enhancement. CT is superior for detecting calcification.
• Three morphological patterns: tubular (cylindrical enlargement along the entire optic nerve), globular (ring-like enlargement around the optic nerve), and eccentric (aneurysmal deviation to one side of the optic nerve).
• Tram-track sign can also be seen on CT.
• If the lesion extends into the optic canal, optic canal enlargement may be observed.

OCT: Used to evaluate optic disc swelling and retinal ganglion cell complex thickness.

Differential Diagnosis

Differentiation from the following conditions is important:

Disease	Imaging/Examination Key Points
Optic glioma	T2 hyperintensity, enhancement mild to variable
Solitary fibrous tumor (SFT)	STAT6+/CD34+ (immunohistochemistry) 5)
Metastatic disease/leukemic infiltration	Systemic workup, bone marrow/blood findings

Other differential diagnoses include neurosarcoidosis, tuberculosis, syphilis, optic perineuritis, and MOG antibody-associated disease.

Caution: Delay in imaging diagnosis

One facility reported that in 71% of cases, initial imaging resulted in missed or delayed diagnosis. ⁴⁾ Factors contributing to missed diagnosis include lack of consultation with a neuroradiologist, omission of orbital fine-cut imaging, and imaging without contrast. When orbital ONSM is suspected, it is important to request orbital MRI with contrast and fat suppression using thin slices.

Biopsy principle: If typical imaging findings are present, biopsy is unnecessary. Even biopsy alone via surgery leads to a very poor visual prognosis, so it should not be performed when useful vision remains.

Q Is biopsy necessary for the diagnosis of optic nerve sheath meningioma?

A

If typical MRI findings (tram-track sign, doughnut sign) are present, biopsy is unnecessary. The optic nerve and ONSM share pial blood supply, and surgical procedures including biopsy carry a high risk of damaging the optic nerve. Since “even biopsy alone leads to a very poor visual prognosis,” surgical intervention should be avoided when useful vision remains.

5. Standard treatment

Observation

If the patient is asymptomatic or visual function decline is mild and slow, careful observation with regular imaging and visual function assessments (visual acuity, visual field, OCT) is chosen. Other than poor visual acuity at initial visit, there are no clear prognostic factors, and visual acuity changes during the observation period vary widely.

Radiation Therapy (First-line treatment when intervention is needed)

Radiation therapy is indicated when visual function decline progresses or intracranial extension is present. If optic nerve atrophy is not severe, stabilization or improvement of visual acuity and visual field can be expected. Stereotactic radiotherapy uses linear accelerator, Gamma Knife, or CyberKnife, and the device is selected based on tumor size and shape.

Main radiation therapy modalities

IMRT

Intensity-modulated radiation therapy: Reported to stabilize or improve visual acuity in 81% of cases.

Dose: 50.4 Gy in 28 fractions is standard. ²⁾⁴⁾

fSRT

Fractionated stereotactic radiotherapy: Reported to stabilize or improve visual field in 83.3–100% of cases.

High dose concentration to the optic nerve.

SRT, GKRS, CyberKnife

Stereotactic radiotherapy, Gamma Knife, CyberKnife: Reported MRI tumor control rate of 100% at 68 months.

For single fraction, 15 Gy (50% isodose) has been used in some cases. ¹⁾

Proton beam therapy: Lower scatter dose may reduce late toxicity. It is considered beneficial for lesions near the pituitary gland, and in pediatric cases, it is also considered from the perspective of reducing secondary cancer risk. Research on ONSM is limited. In pediatric cases, there is a report of 50.4 CGE in 28 fractions. ⁴⁾

Surgical Treatment

When useful vision remains, surgical resection is generally not recommended. The optic nerve and ONSM share pial blood supply, and resection carries a high risk of worsening vision.

Indications for considering surgical treatment:

• Blind eye with severe proptosis or cosmetic deformity
• Risk of intracranial extension
• Risk of spread to the contralateral optic nerve

Optic canal decompression or optic nerve sheath fenestration may be performed before radiotherapy to reduce local pressure (especially in children). ⁴⁾

Precautions and Side Effects of Treatment

Complications of radiotherapy include radiation retinopathy, radiation-induced optic neuropathy (RION), iritis, cataract, dry eye, and hypopituitarism. Early side effects may include temporary erythema, alopecia, and headache. Re-irradiation in previously irradiated cases has been reported to increase RION risk tenfold (Milano et al., 34 studies, 1,578 cases). ¹⁾ Ocular neuromyotonia has also been reported after re-irradiation, and carbamazepine is effective for control. ²⁾

Q How much does vision improve after radiotherapy?

A

Depending on the treatment modality, fractionated stereotactic radiotherapy (fSRT) achieves stabilization or improvement of visual field or acuity in 83.3–100% of cases, and IMRT in 81% of cases. However, patients with better pre-treatment vision have a better prognosis, and improvement is unlikely in advanced cases with severe optic atrophy.

6. Pathophysiology and Detailed Pathogenesis

Gross and Histopathology of the Tumor

Macroscopically, the tumor appears as a well-circumscribed round mass that does not infiltrate the optic nerve tissue but grows concentrically around it. It spreads along the long axis, and when it extends intracranially, there is a risk of spread to the contralateral visual pathway.

Histological types are multiple; the main ones are listed below.

• Meningothelial type: Basic type. Characterized by whorl formation.
• Others: fibroblastic, transitional, psammomatous, secretory, etc. There is also a subtype (psammomatous) in which many psammoma bodies are formed.
• Approximately 20% are reported to show malignant features, but the histological type itself has little correlation with prognosis.

Immunohistochemistry: EMA positive, PR positive, SSTR2A positive. Ki-67 is low in Grade 1 (2–3%). Negative findings for STAT6 and CD34 are important for differentiation from solitary fibrous tumor (SFT). ⁵⁾

WHO classification: Grade 1 (benign, >80% of all meningiomas), Grade 2 (atypical, 4–19 mitoses/10 HPF + brain invasion), Grade 3 (malignant, >20 mitoses/10 HPF).

Mechanisms of RCVC and related complications

• Formation of RCVC (retinochoroidal collateral vessels): Chronic compression of the central retinal vein by the retrobulbar tumor leads to formation of collateral vessels (shunts) between the retinal and choroidal circulations.
• Mechanism of peripapillary choroidal neovascularization (PPCNV) formation (rare complication): Hypotheses include angiogenesis promotion due to anatomical dehiscence and circulatory disturbance (ischemia/nutritional deficiency), and VEGF accumulation within the compartmentalized perioptic SAS (meningiomas are highly vascular tumors with increased VEGF expression). ³⁾
• Dilation of the perioptic SAS (subarachnoid space): Cerebrospinal fluid accumulation posterior to the tumor compartmentalizes the SAS, contributing to papilledema. ³⁾

7. Latest research and future perspectives (research-stage reports)

For patients: Please read this

The following content is currently at the research stage or under clinical trial and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Ga-68 PET/CT (somatostatin receptor ligand PET): Functional imaging using somatostatin receptors, reported to have approximately 10% higher sensitivity and selectivity compared to MRI, and also useful for predicting tumor growth rate. Not necessary in typical cases, but may be useful for evaluating atypical cases or tumor activity.

Vakharia et al. (2021) reported a case of a 54-year-old woman whose tumor regrew and vision declined to hand motion 7 years after initial IMRT (50.4 Gy/28 fractions). She underwent salvage Gamma Knife radiosurgery (GKRS) at 15 Gy (50% isodose). Six months later, her vision dramatically recovered to 20/20-1. OCT showed persistent thinning of the retinal nerve fiber layer (99 μm → 85 μm). In patients with prior radiation, the risk of RION is reported to increase 10-fold (Milano et al., 34 studies, 1,578 cases). The steep dose fall-off of GKRS is considered advantageous for tumors with an exophytic growth pattern. ¹⁾

Sharieff et al. (2021) performed re-irradiation (4,000 cGy/16 fractions, IMRT) for a recurrence 27 years after initial irradiation (4,005 cGy/15 fractions). After re-irradiation, visual acuity recovered to 20/15 and visual field improved by 71%. Side effects included dry eye, transient color vision disturbance, and ocular neuromyotonia (managed with carbamazepine). This is considered the first reported case of ONSM re-irradiation in the literature. ²⁾

Endoscopic endonasal approach: For selected exophytic tumors, case reports have achieved resolution of visual symptoms and gross total resection. Research on expanding the indications for this procedure is ongoing.

Mifepristone (antiprogesterone agent): Meningiomas often express progesterone receptors, and its use is considered in rare refractory cases. It is not standard treatment, and its efficacy is not established. ⁴⁾

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8. References

1. Vakharia K, Hasegawa H, Stafford SL, Link MJ. Salvage Radiosurgery for Optic Nerve Sheath Meningioma. Cureus. 2021;13(7):e16450.
2. Sharieff JA, Melson A, Algan O. Treatment of Recurrent Optic Nerve Sheath Meningioma With a Secondary Course of Radiotherapy. Cureus. 2021;13(9):e17935.
3. Liao WP, Cheng CK, Peng PH. Peripapillary choroidal neovascularization associated with optic nerve sheath meningioma. Taiwan J Ophthalmol. 2022;12:360-363.
4. Wang DX, Walker CS, Ahmedin YA, et al. A Cavernous Sinus Meningioma in a Child with Progressive Bilateral Visual Loss Ultimately Attributed to Unsuspected Optic Nerve Sheath Meningiomas. Case Rep Ophthalmol. 2026;17:57-63.
5. Williams M, Ahmad T, Chin LS, et al. Clinical, Pathologic, and Radiologic Features of Orbital Solitary Fibrous Tumors and Meningiomas. Cureus. 2021;13(11):e19678.