Optic nerve sheath meningioma (ONSM) is a benign tumor originating from the meningeal layers (arachnoid cells) of the optic nerve sheath. It is the most common form of primary orbital meningioma and shows a distinct predilection for middle-aged women (female/male ratio 3:1). Slowly progressive vision loss is the most common presenting complaint, and the classic clinical triad consists of optic atrophy, vision loss, and optociliary shunt vessels. The tram-track sign (axial) and doughnut sign (coronal) on MRI are pathognomonic findings. Calcification is common and supports the diagnosis on CT. The tumor encases the optic nerve but the nerve itself remains separate from the tumor; this feature is the key distinguishing point from optic nerve glioma.
Age Range
30-65
Peak Age
45
Gender
Female predominant
Prevalence
Rare
ONSM originates from meningothelial (arachnoid cap) cells in the arachnoid layer of the optic nerve sheath. These cells are concentrated in granulations of the arachnoid villi and form tumors through neoplastic transformation. The tumor shows a tubular or eccentric growth pattern around the optic nerve, compressing the nerve and causing progressive axonal damage and demyelination; this forms the pathophysiological basis of slowly progressive vision loss. Chronic optic nerve compression leads to obstruction of retinal venous return and development of optociliary shunt vessels (retinochoroidal venous collaterals). Psammoma bodies (concentric calcified laminations) are common in the tumor and represent the histological correlate of calcification on CT. Hormonal receptor expression (progesterone receptor positivity) partially explains the higher frequency in women.
Tubular enhancement around the optic nerve on axial contrast-enhanced MRI (tram-track sign) and ring-shaped enhancement on coronal sections (doughnut sign) are pathognomonic findings of optic nerve sheath meningioma. The enhancing tumor encases the optic nerve but the nerve itself does not enhance and is preserved as a central hypointense structure. These findings directly demonstrate that the tumor is a structure separate from the nerve (sheath-derived).
Tubular enhancement around the optic nerve is seen on axial contrast-enhanced fat-suppressed T1-weighted images, with the nerve itself continuing to remain hypointense without enhancement. This appearance is called the 'tram-track sign' and is the pathognomonic MR finding of ONSM. The enhancing sheath component of the tumor creates parallel lines on each side of the nerve. Thin-section (2-3 mm) axial images allow optimal evaluation of this finding. Fat suppression technique eliminates orbital fat signal, making the enhancement pattern much more conspicuous.
Report Sentence
Tubular enhancement around the optic nerve (tram-track sign) is noted on axial contrast-enhanced fat-suppressed T1-weighted images, with the nerve itself not enhancing, consistent with optic nerve sheath meningioma.
Ring (doughnut)-shaped enhancing tumor tissue surrounding the optic nerve is seen on coronal contrast-enhanced fat-suppressed T1-weighted images. The central hypointense area represents the optic nerve, and the peripherally enhancing ring represents the meningioma. The doughnut sign is the coronal plane equivalent of the tram-track sign and confirms the ONSM diagnosis. Whether the tumor is eccentric (grown more to one side) or concentric (equal thickness) reflects different growth patterns. Coronal images are also superior to axial images for evaluating tumor extension into the optic canal.
Report Sentence
Ring-shaped enhancement surrounding the optic nerve (doughnut sign) is noted on coronal contrast-enhanced images, consistent with optic nerve sheath meningioma.
Tubular, punctate, or plaque-like calcification around the optic nerve is seen on non-contrast CT. Calcification reflects psammoma bodies (concentric calcified laminations) within the tumor and is a characteristic histopathological feature of meningiomas. Since calcification is rare in optic nerve glioma, it is an important clue in differential diagnosis. Thin-section (≤1 mm) axial CT and bone window reformatted images optimally show the distribution and pattern of calcification. Calcification in a tubular pattern is called tram-track calcification and is the pathognomonic finding on CT.
Report Sentence
Tubular pattern calcification around the optic nerve is noted on non-contrast CT, consistent with optic nerve sheath meningioma.
ONSM generally shows isointense or slightly hypointense signal relative to the optic nerve on T2-weighted images. This T2 isointensity-hypointensity reflects the fibrous and cellular structure of the tumor, and prominent hypointense foci are seen in calcified areas (susceptibility effect from calcification). The optic nerve can be distinguished from the tumor by T2 signal difference: the nerve generally appears slightly more hyperintense compared to the tumor. Perineural CSF cleft (thin CSF layer between optic nerve and tumor) may be seen as a T2 hyperintense thin line and confirms that the tumor is a structure separate from the nerve.
Report Sentence
A mass with isointense-to-slightly hypointense signal characteristics is noted around the optic nerve on T2-weighted images, with perineural CSF cleft confirming tumor tissue separate from the nerve.
A tubular or fusiform mass showing intense homogeneous enhancement around the optic nerve is seen on contrast-enhanced CT. The degree of enhancement is intense, reflecting the rich vascularity of meningiomas. The optic nerve itself does not enhance and can be distinguished as a central hypodense structure within the tumor (although less conspicuous compared to MRI). Tubular enhancement pattern is the CT equivalent of the tram-track sign. On bone window reformatted images, optic canal widening and hyperostosis (bone thickening) indicate chronic growth of the meningioma.
Report Sentence
An intensely homogeneously enhancing tubular mass around the optic nerve is noted on contrast-enhanced CT, with optic canal widening on bone window images, consistent with optic nerve sheath meningioma.
Thickening of the optic nerve sheath is seen on B-mode orbital ultrasonography, and tumoral tissue of hypoechoic-to-medium echogenicity can be distinguished around the nerve. High internal reflectivity on A-scan ultrasonography is a characteristic feature of meningiomas and is distinguishing from low-reflectivity gliomas. Optic nerve diameter appears increased, and nerve-tumor distinction is not always clear on B-mode. Increased vascularity within the tumor may be seen on Doppler ultrasonography. Ultrasonography can be used as a screening tool but MRI is required for definitive diagnosis and extent evaluation.
Report Sentence
Thickening of the optic nerve sheath with high internal reflectivity on A-scan is noted on orbital ultrasonography, findings consistent with meningioma; MRI is recommended for definitive evaluation.
Criteria
Tumor is confined to the intraorbital segment of the optic nerve without intracanalicular or intracranial extension. Most common form and generally has better prognosis.
Distinct Features
Tram-track and doughnut signs are classically seen on MRI. No optic canal widening. Radiation therapy (stereotactic fractionated radiotherapy or IMRT) is the main treatment option for vision preservation. Surgery is generally not recommended because of high risk of damage to the optic nerve.
Criteria
Tumor extends through the optic canal into the intracranial space. Optic canal widening is seen on bone window CT. Intracranial component may be small or large.
Distinct Features
Size and location of the intracranial component are critical in treatment planning. Radiation therapy field must also cover intracranial extension. When surgical approach is needed, combined orbital approach with craniotomy is applied.
Criteria
Secondary extension of a primary intracranial meningioma (such as sphenoid wing, tuberculum sellae, clinoid meningioma) into the optic canal and orbit. Unlike primary ONSM, the intracranial component is larger and a dural tail may be seen.
Distinct Features
The intracranial source meningioma is associated with a broad dural base. Dural tail sign (enhancing dural thickening) indicates the intracranial source meningioma. Treatment approach is directed at the primary intracranial tumor.
Distinguishing Feature
In optic nerve glioma, the nerve ITSELF shows fusiform enlargement and enhances; in ONSM the SHEATH around the nerve enhances and the nerve is preserved. Glioma is seen in children, ONSM in middle-aged women. Calcification is rare in glioma, common in ONSM. Kinking pattern in glioma, tram-track/doughnut sign in ONSM. NF1 association exists in glioma, not in ONSM.
Distinguishing Feature
Idiopathic orbital inflammation may show diffuse inflammatory infiltration around the optic nerve but calcification is absent and rapid response to steroid treatment supports the diagnosis. May be bilateral. Acute pain and rapid onset clinically differ from the chronic indolent course of ONSM.
Distinguishing Feature
Orbital lymphoma may show encasement around the optic nerve but tram-track/doughnut sign is not typical. No calcification in lymphoma and diffusion restriction is prominent (low ADC). Lymphoma is typically a homogeneous mass located in the lacrimal gland or extraconal space, moulding to structures without bone destruction.
Distinguishing Feature
In secondary orbital extension of intracranial meningioma, a large intracranial component, broad dural base, and dural tail sign are seen. In primary ONSM, the intracranial component is absent or small. Sphenoid wing meningioma may invade the optic canal but the primary lesion is in intracranial location.
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
6-12 ayda bir MR ile tümör boyutu ve uzanım takibi; görme muayenesi (görme keskinliği, görme alanı, renkli görme) ve optik koherens tomografi (OCT). Progresyon durumunda radyoterapi değerlendirilmeli.Vision preservation is the most critical goal in ONSM management. Observation is the primary approach in asymptomatic or stable patients. For progressive vision loss, stereotactic fractionated radiotherapy (SRT) or intensity-modulated radiation therapy (IMRT) is standard treatment with 85-95% vision stabilization/improvement rates. Surgery is generally not recommended because the risk of optic nerve damage is very high; only tumor excision in advanced cosmetic deformity or already blind eye may be considered. Radiation doses are typically applied as 50-54 Gy (1.8 Gy/fraction). Treatment decisions must be individualized in NF2-associated bilateral ONSM.
Slow-growing benign tumor. Observation may suffice if vision is preserved. Fractionated stereotactic radiotherapy (FSRT) is the preferred treatment for progressive vision loss. Surgery carries risk of optic nerve damage.