Optic nerve meningioma

Key points

  • Definition: Optic nerve meningioma (ONM) is a rare, benign tumor arising from arachnoid cap cells in meninges covering the optic nerve (ON).

  • Synonym: Optic nerve sheath meningioma (ONSM).

  • Classic Clue: Appears as an enhancing mass surrounding the nonenhancing ON with “tram track” calcifications and perioptic cysts.

  • The second most common ON tumor.

  • Calcification is a characteristic feature on computed tomography (CT).

  • Main differential diagnosis is optic nerve glioma (ONG) distinguishable by the absence of calcification.


Computed tomography features

  • High-density mass surrounding the ON.

  • Calcification in 20% to 50% of cases.

  • Postcontrast enhancement demonstrates the “tram track” or “sandwich” sign with the ON sandwiched between tumor masses.

  • Calcified ONMs may show the above appearance even without contrast.

  • Bony changes may include erosion and hyperostosis of the sphenoid and/or optic canal enlargement.

  • Computed tomography (CT) recommendations:

    • CT is less preferred but may be the first imaging study performed.

      • Radiation to the orbit is undesirable.

      • Less effective in demonstrating extent of disease.

      • Better at detecting calcifications. When present, calcifications are characteristically linear or punctate.

      • ONM may be isodense on non-enhancing (NE) CT depending on the amount of calcification.

      • “Tram tracking,” which may result from calcification or tumor enhancement

    • Calcification typically spares the distal ON and the optic disk.

Magnetic resonance imaging features

  • Classic imaging appearance:

    • Isointense/or slightly hypointense (to brain) on T1-weighted images.

    • On T2-weighted images tumor signal varies inversely to the degree of calcification, from slightly hyperintense to hypointense.

    • More calcification produces a lower T2- signal.

    • Cerebrospinal fluid (CSF) in the dilated subarachnoid space gives characteristic perioptic cysts, best demonstrated on T2 weighted images (or by inversion recovery).

    • T1 Gd with mild enhancement is better demonstrated with fat saturation.

    • “Tram track” perineural enhancement is classic, but not pathognomonic. See Differential Diagnosis section.

    • The intracranial component of this tumor may enhance more than the intraorbital component.

  • Contrast enhanced magnetic resonance imaging (MRI) is:

    • The preferred imaging procedure.

    • MRI with Gd and fat saturation can detect and demarcate ONM with a precision not attainable with any other current imaging technique.

    • Better at defining disease extent, which may involve orbital apex, optic canal, and intracranial structures.

    • Better at excluding intracranial origin of en plaque meningioma from planum sphenoidale and tuberculum sellae.

    • It is noteworthy that 90% of optic nerve gliomas (ONGs) originate outside the orbit.

    • Better at demonstrating other findings in patients who have or may have neurofibromatosis (NF).

    • Allows sequential follow-up of patient without increasing cumulative radiation dose.

    • Fat saturation imaging is helpful in evaluating subtle lesions.

Clinical issues


Childhood ONM

  • Rare.

Adult ONM

  • Presentation: Progressive vision loss or proptosis.

    • Usually unilateral.

  • Two thirds occur in middle aged females.

  • Mean onset age 45 to 49 years (depending on series).

Younger patients

  • Suggests neurofibromatosis type 2 (NF2).

  • NF2 is a risk factor for ONM.

    • 9% of patients with ONM have NF2.


  • Approximately 10,000 meningiomas diagnosed in the United States annually.

  • Approximately 100 ONMs diagnosed in the United States annually.

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