Optic pathway gliomas are relatively uncommon tumours, with a variable clinical course and usually seen in the setting of neurofibromatosis type I (NF1). Histologically the majority are pilocytic astrocytomas.
They are characterised by imaging by an enlarged optic nerve seen either on CT or MRI. Usually showing low T1 and a high central T2 signal on MRI images, enhancement is variable.
These tumours have sometimes been divided into optic pathway gliomas and hypothalamic gliomas (not to be confused with hypothalamic hamartomas). In cases where a tumour is confined to the optic nerves (Dodge stage 1 – see below), they can safely be referred to as optic nerve gliomas. Often, however, they are either centred on or extend to involve the chiasm and optic radiations. In such cases, they are difficult to distinguish from hypothalamic gliomas and such a distinction is in most instances artificial. In such more posterior cases, the term hypothalamic-optochiasmatic glioma is perhaps more accurate although it certainly does not roll off the tongue.
As such, generally, the term optic pathway glioma is favoured, recognising that there may be involvement of the hypothalamus.
Optic pathway gliomas typically present in children, accounting for 10-15% of supratentorial tumours in this age group, and are often in the setting of neurofibromatosis type 1 (NF1) (10-63%) 3. In this setting, the tumours are often low-grade and indolent.
Males and females are approximately equally affected.
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 varied depending on the extent and location of the tumour.
Decreased vision (63%) 5 is usually evident and can be documented with visual field examination if the child is old enough. In orbital optic nerve gliomas, eventually, mass effects will also occur with proptosis.
Involvement of the hypothalamus may result in polyuria/polydipsia 4, as well as obesity, sexual precocity and endocrine dysfunction (e.g. short stature). Diencephalic symptoms include a change in alertness and hyperactivity.
In large intracranial tumours symptoms of raised intracranial pressure, focal neurological deficits and hydrocephalus from distortion of the midbrain may also be encountered.
Most optic pathway gliomas are pilocytic astrocytomas (WHO grade I), although their imaging characteristics are not specific with regard to their histologic features. Varying degrees of cystic change and enhancement are demonstrated. The tumours may appear smooth, fusiform, eccentric, or lobulated.
The most widely accepted classification of optic pathway gliomas is the Dodge classification that was first proposed by Dodge et al. in 1958 8. The Dodge classification divides these tumours into just three groups based on anatomical localisation:
- stage 1: optic nerves only
- stage 2: chiasm involved (with or without optic nerve involvement)
- stage 3: hypothalamic involvement and/or other adjacent structures
A more recent modification of the Dodge classification has been proposed which further subdivides each stage 9.
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 a tumour is not confined to the orbit. Additional findings of neurofibromatosis type 1 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.
MR imaging is optimal for showing the relationship of the mass to the hypothalamus, optic chiasm, and infundibulum as well as the intraorbital and intercanalicular components of the mass. Large tumours are typically heterogeneous with cystic and solid components.
- T1: enlargement, often iso to hypointense compared to the contralateral side
- T1 C+ (Gd): enhancement is variable
- hyperintense centrally
- thin 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 a 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 a 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 a tumour is located at the chiasm, the differential should include pituitary region masses.
- 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
- 7. Peter C. Burger, Bernd W. Scheithauer. Tumors of the Central Nervous System. ISBN: 9781933477015
- 8. Dodge HW, Love JG, Craig WM, Dockerty MB, Kearns TP, Holman CB, Hayles AB. Gliomas of the optic nerves. A.M.A. archives of neurology and psychiatry. 79 (6): 607-21. Pubmed
- 9. Taylor T, Jaspan T, Milano G, Gregson R, Parker T, Ritzmann T, Benson C, Walker D. Radiological classification of optic pathway gliomas: experience of a modified functional classification system. The British journal of radiology. 81 (970): 761-6. doi:10.1259/bjr/65246351 - Pubmed
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