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Optic Pathway Glioma

Summary

  • Optic pathway gliomas (OPGs) are low-grade astrocytomas affecting the optic nerves, chiasm, and/or optic tracts
  • Commonly associated with neurofibromatosis type 1 (NF1)
  • Typically present in childhood with visual disturbances, proptosis, or endocrine dysfunction

Pathophysiology

  • Arise from glial cells (primarily astrocytes) of the optic pathway
  • WHO grade 1 pilocytic astrocytomas in most cases
  • May involve:
    • Optic nerves
    • Optic chiasm
    • Optic tracts
    • Hypothalamus (in some cases)
  • Associated with NF1 mutations in about 30% of cases

Demographics

  • Most common in children, with 75% diagnosed before age 10
  • Accounts for 3-5% of all paediatric brain tumours
  • Slightly higher incidence in females
  • 15-20% of NF1 patients develop OPGs

Diagnosis

  • Clinical presentation:
    • Visual disturbances (decreased acuity, visual field defects)
    • Proptosis
    • Strabismus
    • Nystagmus
    • Endocrine dysfunction (if hypothalamic involvement)
  • Ophthalmologic examination:
    • Optic disc pallor or swelling
    • Visual field testing
  • Endocrine evaluation if hypothalamic involvement suspected

Imaging

  • MRI is the imaging modality of choice
    • T1-weighted: Iso- to hypointense
    • T2-weighted: Hyperintense
    • FLAIR: Hyperintense
    • T1 post-contrast: Variable enhancement patterns
  • CT:
    • Hypodense or isodense masses
    • Calcifications uncommon
  • Key imaging features:
    • Fusiform enlargement of optic nerves
    • "Dotted i" sign: chiasmatic involvement with posterior extension
    • Hypothalamic involvement may appear as a suprasellar mass

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  • A right sided orbital optic nerve glioma caused fusiform dilatation and hyperintensity of the optic nerve without enhancement.

Treatment

  • Management depends on:
    • Tumour location and extent
    • Presence of NF1
    • Visual function
    • Rate of progression
  • Options include:
    • Observation with serial imaging and ophthalmologic exams
    • Chemotherapy:
    • First-line for most paediatric cases
    • Carboplatin-based regimens common
    • Surgery:
    • Limited role due to risk of visual loss
    • May be considered for large chiasmatic/hypothalamic tumours causing mass effect
    • Radiation therapy:
    • Generally avoided in young children due to long-term sequelae
    • May be considered in older children or adults with progressive disease
  • Prognosis:
    • Generally favourable, with 5-year progression-free survival >90%
    • NF1-associated OPGs tend to have a more indolent course

Differential diagnosis

Differential Diagnosis Differentiating Feature
Optic neuritis Acute onset, pain with eye movement, often unilateral
Craniopharyngioma Calcifications on imaging, suprasellar location
Meningioma Dural tail sign on MRI; peripheral "tram-track" pattern; intracranial extension along dura
Pituitary adenoma Sellar location; suprasellar extension compressing chiasm from below; no intrinsic nerve enlargement
Optic nerve sheath meningioma "Tram-track" enhancement on CT; nerve spared centrally; calcifications
Optic neuritis Enhancement of nerve without fusiform enlargement; no mass effect; resolves on follow-up
Multiple sclerosis Short T2 signal in optic nerve without mass effect; periventricular brain lesions; Dawson's fingers
Langerhans cell histiocytosis Lytic calvarial or orbital bone lesions; infundibular thickening; diabetes insipidus on MRI
Orbital lymphoma Homogeneous enhancing mass moulding around orbital structures; no tubular nerve enlargement