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Optic Nerve Glioma

Summary

fleuron

  • Benign, slow-growing tumour of the optic pathway, most commonly pilocytic astrocytoma (WHO grade 1), predominantly affecting children
  • Strong association with neurofibromatosis type 1 (NF1), presenting with progressive vision loss, proptosis, and optic nerve enlargement
  • MRI demonstrates fusiform optic nerve enlargement with variable enhancement and characteristic "kinked" appearance when involving the optic nerve1

Pathophysiology

  • Most commonly pilocytic astrocytoma (WHO grade 1)
    • Composed of bipolar cells with Rosenthal fibres and eosinophilic granular bodies
    • BRAF-KIAA1549 fusion or BRAF V600E mutations common in sporadic cases
  • Arise from astrocytes within the optic nerve, chiasm, or optic tracts
  • Can extend along the visual pathway:
    • Anterior: intraorbital optic nerve
    • Posterior: optic chiasm, optic tracts, optic radiations
  • Growth patterns:
    • Intrinsic: expansion within nerve sheath
    • Exophytic: growth beyond nerve sheath
    • Perineural: arachnoidal gliomatosis (rare)

Demographics

  • Peak incidence: 4-6 years of age
  • 90% occur before age 20
  • Slight female predominance (1.2:1)
  • Strong association with NF1:
    • 15-20% of NF1 patients develop optic pathway gliomas
    • 10-70% of optic pathway gliomas occur in NF1 patients
  • Bilateral optic nerve gliomas almost pathognomonic for NF1
  • Better prognosis in NF1-associated cases (often indolent course)

Diagnosis

  • Clinical presentation:
    • Progressive vision loss (most common)
    • Proptosis (especially with intraorbital involvement)
    • Strabismus
    • Nystagmus (chiasmal involvement)
    • Optic disc swelling or atrophy
    • Precocious puberty (hypothalamic involvement)
  • Visual field testing: variable defects depending on location
  • Fundoscopy: optic disc oedema, pallor, or atrophy
  • Biopsy rarely performed due to risk of vision loss
  • Diagnosis typically based on imaging in appropriate clinical context

Imaging

  • MRI (modality of choice):
    • T1: isointense to hypointense relative to gray matter
    • T2: hyperintense with fusiform or tubular enlargement of optic nerve
    • T1+C: variable enhancement (typically avid but can be minimal or absent)
    • DWI: usually no restricted diffusion (helps differentiate from malignant gliomas)
    • STIR: hyperintense, useful for orbital imaging
    • Fat-suppressed T1+C: optimal for evaluating orbital and intracanalicular segments
  • Imaging patterns:
    • Fusiform enlargement with "kinked" or buckled appearance
    • Smooth tubular thickening
    • Globular or exophytic masses (chiasmal/hypothalamic involvement)
    • "Pseudo-CSF" sign: peripheral hyperintense cystic areas on T2
  • CT findings:
    • Iso- to hyperdense tubular enlargement
    • Optic canal expansion (chronic cases)
    • Calcification rare
  • Additional findings in NF1:
    • Unidentified bright objects (UBOs) in basal ganglia, brainstem, cerebellum
    • Plexiform neurofibromas
    • Sphenoid wing dysplasia

panels-1

  • A 40-year-old patient presented with a visual field defect and optic nerve swelling that was identified by an optician.
  • Imaging showed a thickened and hyperintense optic nerve with patchy enhancement.

Treatment

  • Often observed (especially indolent NF1-associated tumours); chemotherapy for progression, with radiotherapy avoided in NF1 and young children. Bilateral optic nerve gliomas are essentially pathognomonic of NF1

Differential diagnosis

Differential diagnosis Differentiating feature
Optic nerve sheath meningioma Peripheral "tram-track" or "doughnut" enhancement; nerve itself spared centrally; calcifications common; optic canal wall thickening
Optic neuritis Enhancement of nerve without fusiform enlargement; no mass effect; resolves on follow-up

  1. Shapey et al. Diagnosis and management of optic nerve glioma. 2011. Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia - Open in new tab. ↩