Optic nerve meningioma

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.

Presentation

Incidence

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

• Approximately 100 ONMs diagnosed in the United States annually.