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Optic Nerve Sheath Meningioma

Summary

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  • Rare benign tumour arising from meningothelial cells of the optic nerve sheath
  • Typically presents with gradual, painless vision loss and proptosis
  • Characteristic "tram-track" sign on contrast-enhanced imaging

Pathophysiology

  • Originates from arachnoid cap cells within the optic nerve sheath
  • Grows circumferentially around the optic nerve, causing compression
  • May extend intracranially through the optic canal
  • Histologically similar to intracranial meningiomas

Demographics

  • Accounts for 1-2% of all orbital tumours
  • Female predominance (3:1 female to male ratio)
  • Peak incidence in middle-aged adults (30-50 years)
  • Rare in children, but associated with neurofibromatosis type 2 when present

Diagnosis

  • Clinical presentation:
    • Gradual, painless monocular vision loss
    • Proptosis
    • Optic disc oedema or atrophy
    • Optociliary shunt vessels (in advanced cases)
  • Ophthalmologic examination:
    • Visual acuity testing
    • Visual field testing (typically central or arcuate defects)
    • Fundoscopy
  • Diagnostic criteria:
    • Characteristic imaging findings
    • Clinical presentation
    • Exclusion of other orbital masses

Imaging

  • CT:
    • Fusiform enlargement of the optic nerve
    • Calcifications in 20-25% of cases
    • Hyperostosis of adjacent bone (uncommon)
  • MRI:
    • T1: Isointense to slightly hypointense to brain
    • T2: Variable signal intensity
    • T1 post-contrast:
    • "Tram-track" sign: Circumferential enhancement around a non-enhancing central optic nerve
    • "Doughnut" sign on axial images
    • Fat-suppressed sequences helpful for delineating tumour extent
  • Differential diagnosis:
    • Optic nerve glioma
    • Orbital pseudotumour
    • Sarcoidosis
    • Metastases

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  • 40-year-old patient presenting with left sided proptosis.
  • MRI showed an avidly enhancing lesion filling the orbital apex and encasing the optic nerve.

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  • 45-year-old female with eccentric enhancement of the left optic nerve sheath near the orbital apex.
  • There was very high uptake on the Ga-DOTATATE PET scan.

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  • 35-year-old patient developed worsening orbital swelling during pregnancy.
  • An enhancing mass lesion along the inferior aspect of the optic nerve sheath, causing 2 mm of proptosis, was avid on Ga-DOTATATE PET.

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  • 30-year-old patient presented with proptosis but no visual symptoms.
  • MRI showed proptosis secondary to a large enhancing lesion encasing the optic nerve (red arrow).

Treatment

  • Observation for small, asymptomatic tumours
  • Fractionated stereotactic radiotherapy:
    • First-line treatment for most cases
    • Aims to halt tumour growth and preserve vision
  • Surgery:
    • Reserved for large tumours with significant proptosis or intracranial extension
    • Risk of complete vision loss in the affected eye
  • Systemic therapy:
    • Limited role
    • Hydroxyurea or temozolomide may be considered in select cases
  • Follow-up:
    • Regular ophthalmologic examinations
    • Periodic MRI to monitor tumour size and extension

Differential diagnosis

Differential Diagnosis Differentiating Feature
Optic nerve glioma Intrinsic fusiform enlargement of the nerve itself; no peripheral tram-track enhancement; calcification absent
Orbital pseudotumour Diffuse infiltration of orbital fat and extraocular muscles; no discrete encasing mass; variable enhancement
Orbital lymphoma Homogeneous soft tissue mass moulding to orbital structures; no calcification; may involve lacrimal gland
Orbital metastases Known primary malignancy; irregular margins; bone destruction in aggressive types
Sarcoidosis Enhancing optic nerve with leptomeningeal spread; bilateral optic nerve involvement; no tram-track sign