Pilocytic Astrocytoma (Optic Glioma)

What is it?

Congenital low-grade (WHO Grade 1) astrocytoma of the optic nerves, optic chiasm, and hypothalamus (“optic glioma”)
Usually discovered before age 20 years
Neurofibromatosis type 1 is present in 30–50%
Present in 15% of patients with neurofibromatosis type 1
MRI shows an intrinsic mass in the optic nerve, optic chiasm, and/or hypothalamus
No biopsy is necessary if imaging is distinctive
Chemotherapy is often used but its benefit is uncertain as controlled trials have not been performed
Surgical resection of the optic nerve is reserved for unsightly proptosis when the affected eye has no light perception

Core clinical features
- Stationary or progressive visual loss in one eye or both
- Reduced visual acuity and visual field defects in one or both eyes
- Afferent pupil defect
- Optic discs appear normal or pale (or elevated if an orbital tumor involves the distal optic nerve)
Possible accompanying clinical features
- Monocular pendular nystagmus (often vertical)
- Seesaw nystagmus
- Proptosis (if there is a large tumor in the orbit)
- Iris hamartomas called “Lisch nodules” (sign of neurofibromatosis Type 1) should be present if the patient is aged above 10 years
- Eyelid plexiform neuroma

Order orbit-based MRI, which is usually diagnostic
Biopsy the lesion only if the imaging features are not classic or a large exophytic component is present

Tumor size and visual function often remain stable in untreated patients
Visual decline may be caused either by tumor growth, tumor production of extracellular matrix, or reactive meningeal hyperplasia
Intraorbital tumors may have an intracranial component, but they do not spread intracranially
Trap: do not treat a tumor apparently confined to the orbit, except when there is disfiguring proptosis and a blind eye, in which case excision of the intraorbital optic nerve, sparing the eye and extraocular muscles, may be indicated
Place a ventriculoperitoneal shunt for obstructive hydrocephalus
Consider chemotherapy for patients under age 9 whose tumors are growing, involving the optic chiasm or hypothalamus, causing severe vision loss, worsening vision, or hypothalamic dysfunction
Trap: there are no large controlled trials to affirm that chemotherapy is effective in this condition, but newer agents, including MEK inhibitors, are showing promise
Consider radiation therapy as an alternative to chemotherapy for patients older than 9 years
Trap: radiation therapy in patients with NF 1 carries a high risk of later occlusive vasculopathy and secondary tumors
These tumors may rarely cause severe neuroendocrine morbidity or death