Optic nerve glioma overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]
Overview
Optic nerve glioma is common tumor of the optic nerve. Majority of these tumors are benign but malignant gliomas of the optic nerve can occur. Optic nerve glioma is a slow-growing brain tumor that arises in or around the optic nerves. As the tumor progresses, it can press on the optic nerve and worsen a child's vision.
Classification
Optic pathway gliomas are classified under the WHO’s classification of a grade I pilocytic astrocytoma, usually Juvenile Pilocytic Astrocytomas (JPA). Occasionally pathology is positive for grade II fibrillary astrocytoma. Optic nerve gliomas may be classified into two subtypes based on anatomic location, and whether or not they are associated with neurofibromatosis type 1. Optic nerve gliomas may be classified according to anatomic location into two subtypes: anterior tumors and posterior tumors.
Pathophysiology
Genes involved in the pathogenesis of optic nerve glioma include BRAF-KIAA, tumor suppressor genes and chromosomes 7q34 and 17q. On gross pathology, smooth and fusiform intradural lesion is characteristic findings of optic nerve glioma. On microscopic histopathological analysis, low grade spindle shaped pilocytic astrocytes & glial filaments, with the presence of numerous Rosenthal’s fibers are characteristic findings of optic nerve gliomas.
Causes
There is no established cause for optic nerve glioma.
Differential Diagnosis
Optic nerve glioma must be differentiated from other diseases that cause optic nerve enlargement and tumors located at optic chiasm, such as optic nerve meningioma, orbital pseudotumor, optic neuritis, orbital lymphomas, metastasis, fibrous dysplasia, paranasal mucocele, Lymphoma, rhabdomyosarcoma, neurofibromatosis, perioptic haemorrhage, erdheim-Chester disease, juvenile xanthogranuloma, medulloepithelioma, retinoblastoma, krabbe disease, optic nerve and chiasm glioma such as germinoma and sarcoidosis, and optic chiasm glioma extending into the hypothalamus such as pituitary adenoma, craniopharyngioma, malignant astrocytoma, dermoid cyst, chordoma, colloid cyst, fibrous dyplasia, sarcoidosis, histiocytosis X, tuberculous granuloma, and hemangloendothelioma.[1]
Epidemiology and Demographics
The prevalence of optic nerve glioma is estimated to be 1 per 100, 000 patients presenting with eye complaints. Optic nerve gliomas affects girls and boys equally. There is no racial predilection to the optic nerve glioma.[2]
Risk Factors
There are no established risk factors for optic nerve gliomas.
Screening
According to the United States Preventive Services Task Force, screening for optic nerve glioma is not recommended. It is recommended that all children with NF-1 have their vision checked every year by an ophthalmologist.
Natural History, Complications and Prognosis
If left untreated, less than 5 percentage of patients with optic nerve gliomas may progress to develop blindness. Common complications of optic nerve glioma include decreased vision, blindness, growth hormone deficiency, precocious puberty, and hydrocephalus. Prognosis is generally good in most patients with optic pathway gliomas. Most optic nerve gliomas are benign and produce slowly progressive visual loss associated with variable proptosis and anterior or posterior optic neuropathy.
History and Symptoms
Symptoms of optic nerve glioma include proptosis, unilaterl or bilateral visual impairment, nystagmus, squinting, obstructive hydrocephalus and diencephalic syndrome.
Physical Examination
Common physical examination findings of optic nerve glioma include nystagmus, strabismus, proptosis, visual impairment, afferent pupillary defect, edema and/or pallor of optic disc, torticollis and deficits of cranial nerve II.
Laboratory Findings
There are no diagnostic lab findings associated with optic nerve glioma.
Electrocardiogram
There are no electrocardiogram findings associated with optic nerve glioma.
Chest X Ray
There are no chest x ray findings associated with optic nerve glioma.
CT Scan
On Head and neck CT, optic nerve glioma is characterized by variably enlarged and elongated optic nerve with kinking or buckling.
MRI Scan
On Head and neck MRI, optic nerve glioma is characterized by isointense to hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI.
Echocardiography
There are no echocardiography findings associated with optic nerve glioma.
Other Imaging Findings
Other imaging studies for optic nerve glioma include cerebral angiography, which may show a space-occupying mass.
Other Diagnostic Studies
Other diagnostic studies for optic nerve glioma include visual field tests, biopsy, and cerebral angiography.
Medical Therapy
The mainstay of therapy for optic nerve glioma is chemotherapy, radiation therapy, and hormone replacement therapy.
Surgery
Surgery is not the first-line treatment option for patients with optic nerve glioma. Surgical excision is usually reserved for patients with either progressive proptosis, blindness, exophytic chiasm tumor causing mass effect, hydrocephalus, or with increased intracranial pressure.
Primary Prevention
Effective measures for the primary prevention of optic nerve glioma include regular eye exams in patients with neurofibromatosis type 1.
Secondary prevention
Secondary prevention strategies following optic nerve glioma include lifelong follow-up care which further includes a visit to a clinic every year for screening of tumor recurrence, management of disease complications, and management of side-effects of treatment.