Optic nerve glioma
Optic nerve gliomas are relatively uncommon tumours, with a variable clinical course and usually seen in the setting of neurofibromatosis type I (NF1).
They are characterised on imaging by an enlarged optic nerve seen either on CT or MRI. Usually showing low T1 and high central T2 signal on MRI images, enhancement is variable.
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.
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.
Radiographs 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 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 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
- 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 some 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 the 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 the 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 (proptosis, intracranial mass effect) 3.
The 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.
Pituitary region masses
- pituitary adenoma (commonest in the adult population)
- hypothalamic astrocytoma/glioma
- chiasmatic astrocytoma
- optic nerve glioma
- dermoid (CNS) / epidermoid / intracranial teratoma
- pituitary metastases
- granular cell tumour of the pituitary (pituitary choristoma)
- pilocytic astrocytoma of the neurohypophysis (infundibuloma)
- cellular infiltrates
- other lesions
- 1. Kanamalla US. The optic nerve tram-track sign. Radiology. 2003;227 (3): 718-9. doi:10.1148/radiol.2273010758 - Pubmed citation
- 2. Hendrix LE, Kneeland JB, Haughton VM et-al. MR imaging of optic nerve lesions: value of gadopentetate dimeglumine and fat-suppression technique. AJR Am J Roentgenol. 1990;155 (4): 849-54. AJR Am J Roentgenol (abstract) - Pubmed citation
- 3. Wright JE, Mcdonald WI, Call NB. Management of optic nerve gliomas. Br J Ophthalmol. 1980;64 (8): 545-52. Br J Ophthalmol (link) - Free text at pubmed - Pubmed citation
- 4. Millar WS, Tartaglino LM, Sergott RC et-al. MR of malignant optic glioma of adulthood. AJNR Am J Neuroradiol. 1995;16 (8): 1673-6. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 5. Müller-Forell WS, Boltshauser E. Imaging of Orbital and Visual Pathway Pathology. Springer Verlag. (2005) ISBN:3540279881. Read it at Google Books - Find it at Amazon
- 6. Sutton D. Textbook of Radiology and Imaging. Churchill Livingstone. (2003) ISBN:0443071098. Read it at Google Books - Find it at Amazon