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Optic nerve glioma

Dr Ayush Goel and Dr Frank Gaillard et al.

Optic nerve gliomas are relatively uncommon tumours, with variable clinical course and often seen in the setting of neurofibromatosis type I (NF1).

Epidemiology

Optic nerve gliomas typically present in children, and often in the setting of NF1 (10-63%) ³. In this setting, the tumours are often low grade and indolent.

In adults, optic nerve gliomas do occur but are very rare and usually aggressive tumours ⁴. In such cases no association with NF1 has been found ⁴.

Clinical presentation

Decreased vision (63%) ⁵ is usually evident and can be documented with visual field examination if the child is old enough. Eventually mass effects will also occur, with proptosis and even intracranial sequelae including symptoms of raised intracranial pressure, focal neurological deficits and hydrocephalus from distortion of the midbrain. Involvement of the hypothalamus may result in polyuria / polydipsia ⁴.

Radiographic features

Plain film

Plain films no longer have any real role to play in the diagnosis of orbital masses, however if performed enlargement of the optic canal may be demonstrated if the tumour is not confined to the orbit. Additional findings of NF1 may also be visible

CT

CT is often the first investigation performed and although not as sensitive as MRI, the diagnosis can often be made, especially if thin slice imaging through the orbits is performed, or coronal and sagittal reconstructions obtained from volumetric data.

The optic nerve is variably enlarged, and the mass may either be fusiform or exophytic in appearance. Additionally the nerve may be elongated with kinking or buckling ⁵.

MRI

MRI is the modality of choice to diagnosis and assessment of the posterior extent of the tumour.

T1 - enlargement, often iso to hypointense compared to the contralateral side
T1 C+ (Gd) - enhancement is variable
T2
- hyperintense centrally
- low signal at the periphery representing the dura ⁵

Treatment and prognosis

These tumours demonstrate variable clinical and radiological progression. In patients with NF1 it is not unusual for these tumours to be quiescent, with little progression demonstrated over a number of years. In others, the tumours are more aggressive with extension along the optic pathways ³.

Treatment options therefore depend on clinical context, as well as location of the tumour at presentation. If it is isolated to one optic nerve, and does not extend to the chiasm, then resection is curative (albeit with loss of vision in that eye). If the tumour extends to the chiasm or more posteriorly then curative resection is not possible, with resection reserved for treatment of mass effects (proposis, intracranial mass effect) ³.

Differential diagnosis

The main differential is that of optic nerve meningioma however the potential list is much longer including most causes of optic nerve enlargement.
Absence of calcification can be used to differentiate optic nerve glioma from optic nerve sheath meningioma ⁶.

Additionally, when the bulk of the tumour is located at the chiasm, the differential should include pituitary region masses.