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An overview of Optic nerve glioma

Optic nerve gliomas (OPGs) are rare and account for 1-5% of all central nervous system (CNS) tumors in children [1]. They are predominantly seen in childhood as benign tumors, however, the malignant form is occasionally seen in adults. Optic nerve gliomas may be either sporadic or may be associated with Neurofibromatosis1 [2]. The prevalent sporadic type of optic nerve gliomas is usually slow growing, benign (non-cancerous), and occurs in children. The sporadic malignant (cancerous) optic nerve glioma is mostly seen in adults with an aggressive nature and is often fatal despite treatment. The peak age of occurrence of optic nerve gliomas is between 2 and 6 years. Gliomas arise from astrocytes (star-shaped glial cells in the brain and spinal cord) of the optic nerve and visual pathway.


Global scenario


Optic nerve glioma

The prevalence of optic nerve gliomas in the general population has been estimated to be about 1/100,000 [1]. OPGs are relatively rare neoplasms, comprising <1% of all CNS neoplasms in the general population and about 5% of central nervous system tumors in children. The mean age at diagnosis ranges between 2.7 and 5.4 years and the majority (80%–90%) of all patients belong to the first two decades of life. OPG outcome is generally favorable in terms of survival, but not so in terms of vision.


Indian perspective


According to an Indian study, the overall 3-year survival rate was 85.71% and the recurrence rate is 55% with tumor progression on MRI. Indian literature on this topic is limited and in the absence of large series a uniform standard of care treatment guideline is yet to be established.


Signs and symptoms


The clinical features of sporadic optic nerve gliomas of childhood typically comprise slow, unilateral loss of vision, proptosis, decreased color vision, optic disc swelling or atrophy, (decrease in size/loss of tissue) a relative afferent pupillary defect or strabismus [3]. Children will often not complain of loss of vision, but overall, 85% of patients with optic glioma will lose some vision over time whereas approximately 25% will retain vision. Ocular pain (pain in the eye) is not usually a presenting feature. Other symptoms include involuntary eye movements, memory impairment, and daytime sleepiness. Loss of appetite and growth delays may also be present. Patients with optic nerve gliomas may occasionally develop a central retinal vein occlusion, venous stasis retinopathy, iris rubeosis with neovascular glaucoma or ocular ischemic syndrome which are more commonly associated with malignant optic nerve gliomas of adulthood. Based on the origin and clinical presentation, sporadic gliomas confined to the optic nerve may be either intraorbital or intracranial.


Diagnosis


The diagnosis of optic nerve gliomas is based on clinical presentation, ophthalmologic/visual assessment, and radiological imaging which forms the cornerstone in diagnosis followed by confirmation of the histopathological features of the tumor. Ophthalmologic/visual assessment includes extraocular examination followed by assessment of different visual parameters such as visual acuity, visual fields, and fundoscopy [4]. Along with visual assessment, imaging is critical in the diagnosis and management of optic nerve gliomas. Magnetic resonance imaging (MRI) is the preferred method of imaging for optic nerve gliomas, although tumors may also be readily apparent with computed tomography (CT) scans. However, MRI is the preferred method for the definitive evaluation of optic nerve gliomas.


Management


Optic nerve gliomas are usually low-grade tumors although their presentation and clinical course are highly variable and unpredictable. The management of optic nerve gliomas is a highly individualized approach. The goal of all treatment strategies is to preserve vision for as long as possible. Hence, it requires a multidisciplinary approach with a team of specialists including a Pediatrician, Ophthalmologist, Radiologist, Pathologist, Neurosurgeon, Neuro Oncologist, Radiation Oncologist, Dietician, and Psychologist. This multifaceted care underlines the complexity of the disease [5]. The major factor is the timing and sequencing of the modalities of treatment. Most contemporaneous reports focus on the role of observation, chemotherapy, and radiotherapy with less focus on surgery.


Chemotherapy has emerged as the preferred first-line treatment for all optic nerve gliomas, primarily to avoid radiation toxicity. The current standard chemotherapy for optic gliomas consists of vincristine and carboplatin (commonly termed the ‘‘Packer regimen’’). Other chemotherapeutic agents used in treating optic gliomas include temozolomide, thioguanine, procarbazine, and lomustine. Radiotherapy has proved to be the most effective treatment modality in achieving functional improvement in patients with progressive disease or deteriorating functional visual loss, but it is known to have serious side effects. Other than the conventional external beam radiotherapy, new techniques of delivering radiation, including fractionated stereotactic radiotherapy, proton beam radiotherapy and more recently stereotactic radiosurgery have been used in the treatment of optic nerve glioma in the hope of minimizing the risk of radiation induced side-effects. Treatment of optic nerve gliomas with surgical resection is controversial, since, gliomas tend to infiltrate the surrounding structures, and, in most cases, only a limited number of resections can be accomplished. The location of these tumors necessitates surgical resection to involve the visual pathway fibres, which can lead to visual impairment. Therefore, surgical resection is usually limited to tumors confined to one optic nerve or those causing progressive blindness or disfiguring proptosis (bulging eye). Published guidelines recommend reservation of surgery for carefully selected cases where biopsy or debulking can be achieved with limited patient risk. However, concurrent therapy, a combination of chemotherapy followed by radiotherapy is suggested as the treatment of choice considering various factors associated with age, location of the tumor, and tumor progression along with other perpetuating factors [6]. The critical factor is the timing and sequencing of the various modalities of treatment in the management of optic nerve gliomas. In addition to the regular standard care of either single or combined/concurrent therapies such as chemotherapy, surgery and radiotherapy the role of integrative approaches such as diet modification, psychological assessment and treatment for conditions such as depression, anxiety, posttraumatic stress, social withdrawal, and enrolement with interactions in support groups may have a cumulative effect in improving the quality of life of the patients. Additional research will lead to improvements in the visual outcome and increase our understanding of optic nerve gliomas.


Quality of life


For patients with optic nerve glioma, who have a relatively high long term survival rate, preservation of visual function is the primary treatment goal. Patients with optic nerve gliomas frequently experience vision loss from their tumors which impacts the quality of life (QoL). In children, vision loss can significantly affect the development of academic and social abilities, in addition to their acquisition of skills related to self-care, mobility, and independent function. Also, vision loss in children likely contributes to the additional risk for poor school performance and social functioning in a group with a higher risk for cognitive and learning difficulties. Loss of vision during adulthood may have a profound impact on QoL, mortality and employment. Thus, future research with multi-center collaborative studies to better determine the influence of clinical factors on vision specific QoL measures for optic nerve gliomas, is needed.


References


1. Radiation Therapy in Optic Gliomas: A Case Report and a Review of Literature,” J Nucl Med Radiat Ther, Vol 3, Issue 4, 2012, DOI: 10.4172/2155-9619.1000134

2. A. G. Nair, R. S. Pathak, Veena R. Iyer and R. A. Gandhi, Optic nerve glioma: an update Int Ophthalmol, Vol 34, pp999-1005, 2014, DOI 10.1007/s10792-014-9942-8

3. J Goodden et al, The role of surgery in optic pathway/hypothalamic gliomas in children, J Neurosurg Pediatrics, Vol 13, pp1–12, 2014.

4. Iris F, Uri T, Tarik T, Arun R & Eric B, Optic pathway gliomas: a review, CNS Oncol, Vol 2(2), page 143–159, 2013.

5. LM Kaufman and O Doroftel, Optic glioma warranting treatment in children,” Eye, Vol 20, page 1149–1164, 2006.

6. J. Shapey, H.V. Danesh- Meyer and A.H. Kaye, Diagnosis and management of optic nerve glioma,” Journal of Clinical Neuroscience, Vol 18, page 1585–1591, 2011.

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