OPTIC GLIOMA TUMOURS
Although rare, glioma is the commonest optic nerve Tumours in childhood. Optic glioma is associated with neurofibromatosis type 1 (NF1) in a third of cases. Approximately 15 % of patients with NF1 develop an optic glioma (which may be bilateral) though the frequency of symptomatic optic glioma is about 5 % (Lewis et al. 1984; Huson et al. 1988; Singhal et al. 2002). McGaughran et al. (1999) estimated an actuarial risk of optic glioma in NF1 patients of 3.7 % at age 10 years and 6.2 % at age 25 years. A potential association between mutations at the 5′ end of the NF1 gene and the development of optic nerve gliomas has been reported (Sharif et al. 2011).
All patients with optic glioma, and their families should be assessed for evidence of NF1. Histological appearance is of a low-grade (pilocytic) astrocytoma, spontaneous regression may occur, and many consider these Tumours to be congenital hamartomas rather than acquired neoplasms (Riccardi and Eichner 1986). Optic gliomas usually originate in the optic nerves or chiasm, and presentation is usually with visual impairment and/or painless proptosis. Most NF1-associated optic gliomas are orbital.
Computerized tomography (CT) or magnetic resonance image (MRI) scanning will demonstrate optic glioma and differentiate from optic nerve meningioma. The natural history of optic glioma is not well defined. Most are nonprogressive and conservative management is usually preferred. Treatment (surgery or radiotherapy) of optic nerve glioma is indicated for progressive visual loss associated with proptosis. Treatment of chiasmal lesions is more difficult, but again, most are nonprogressive and conservative management is pursued.