Optic nerve glioma - Clinical Tree

Key points

Definition: Optic nerve glioma (ONG) is a type of juvenile pilocytic astrocytoma (grade 1 astrocytoma) that occurs more commonly in children and young adults.
Synonym: Optic pathway glioma (OPG).
Classic clue: Sausage-shaped diffuse fusiform enlargement and “kinking” of the intraorbital optic nerve (ON).
More favorable prognosis compared to other astrocytoma types.
Most common primary neoplasm of the ON.
Bilateral ONG is pathognomonic of neurofibromatosis type 1 (NF1).
Children:
Benign optic glioma.
Low-grade form of neoplasm.
Most often encountered in children.
Adults:
Aggressive glioma (MOG: malignant optic glioma).
Frequently fatal, even with treatment.

Computed tomography (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.
May detect subtle erosion of the optic canal.
Fusiform “sausage-shaped” enlargement of the ON.
Calcifications are rare.
May demonstrate enlargement of the optic canal.
Variable contrast enhancement, with enhancement randomly observed in 50% of cases.

Magnetic resonance imaging (MRI) is:
- Preferred imaging procedure.
- Better at defining disease extent.
- Better at demonstrating other NF1 findings.
- Allows sequential follow-up of a patient without increasing the cumulative radiation dose.
- Fat saturation imaging is helpful in the evaluation of subtle lesions.
Classic imaging appearance.
Tubular/fusiform enhancing ON with mass kinking or buckling of the ON.
T1 isointense to hypointense.
T2 variable—typically hyperintense.
- Low peripheral signal corresponds to the dura.
T1 + Gd.
- Variable enhancement.
- ON cannot be identified as discrete from the ONG.

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