Optic Nerve Glioma
Optic nerve glioma is a slow-growing tumor, which typically affects children. 30% of patients have associated NF1 & those have better prognosis.
Malignant gliomas (glioblastoma) are rare & almost always occur in adult males with a very poor prognosis & almost certain death within one year. Optic-nerve gliomas Comprise about 1% of all intracranial tumors.
About 10% of optic pathway tumors are located within an optic nerve. One third of the tumors involve both optic nerve and chiasm, a further third involve predominantly the chiasm itself, and one fourth is predominantly in the hypothalamus. 5 5% gliomas are multicentric.
Gross pathology of resected tumors reveals a smooth, fusiform intradural lesion. Macroscopically, these tumors may be solid, gelatinous or cystic. Although having certain gross similarities with oligodendrocytes, closer microscopic, ultrastructural and immunostaining techniques have confirmed their low grade spindle shaped pilocytic (hair like) astrocytes & glial filaments, with the presence of numerous Rosenthal’s fibers. Other histologic findings include arachnoid hyperplasia & mucus-substance. The tumor may start in the anterior end of the optic nerve and proceed backwards intracranially or may arise originally from the optic nerve-chiasmal junction. Occasionally, a glioma from the optic tract or the anterior third ventricle region may involve the chiasma and the optic nerve secondarily. About 40% of optic pathway astrocytomas are fibrillary and 60% are pilocytic. Hypothalamic tumors which have invaded the optic chiasm behave differently, showing evidence of local invasion and histologically are not pilocytic in nature but are similar to other cerebral hemisphere gliomas.
Patients with optic pathway gliomas most frequently present in the first decade with a median age of 6.5 years, with slowly progressive visual loss, followed later by proptosis (although this sequence may occasionally be reversed). Acute visual loss due to hemorrhage into the tumor is uncommon. Initial signs and symptoms of malignant gliomas include severe retro-orbital pain, unilateral or bilateral vision loss, and, typically, massive swelling and hemorrhage of the optic nerve head (although disc pallor may also be observed with posterior lesions).
Gradual, painless, unilateral proptosis associated with loss of vision and an afferent pupillary defect is a common presentation. Proptosis often is non-axial, with temporal or inferior dystopia. The optic nerve head is swollen initially but subsequently becomes atrophic. Optociliary collaterals & Central Retinal Vein Occlusion are occasionally seen. Intracranial spread to the chiasm or hypothalamus is rare.
The chiasm is involved in roughly half of cases of optic nerve glioma. Intracranial involvement may be associated with intracranial hypertension as well as decreased function of the hypothalamus and pituitary gland.
Computer Tomography (CT) scans
Bone window setting on CT often reveals widening of the optic canal. In patients with associated NF1, there is typically a fusiform enlargement of the optic nerve with a clear cut margin produced by intact dural sheath. In patients without NF1 the nerve may be more irregular and have some low-density areas.
Magnetic resonance imaging (MRI) scans
MRI often reveals enlargement, kinking, and buckling of the optic nerve. The nerve becomes enlarged and fusiform in shape because of attachment of the investing dura to the periosteum of the optic canal. On T2-weighted images, optic-nerve glioma is hyperintense to cerebral cortex and may appear heterogeneous secondary to cystic degeneration. Gliomas enhance variably and a complete lack of enhancement can also occur. MRI may show cystic degeneration if present.
MRI is useful in showing intracranial extension. It is more sensitive for displaying chiasmatic/ hypothalamic tumors than CT. These tumors are usually hypointense on T1-weighted images and hyperintense on T2 as mentioned and almost always, enhance with gadolinium. On T2, high intensity signal may be seen extending to the lateral geniculate bodies.
The major differential diagnostic considerations when an enlarged optic nerve is identified on imaging are inflammatory (neuritis, infection, or pseudotumor), neoplastic, or the result of increased intracranial pressure. Distinguishing inflammatory from neoplastic processes of the nerves is difficult because both may demonstrate optic-nerve enlargement with or without contrast enhancement. Clinical history can then be used to determine the underlying cause. Unilateral involvement, no pain on extraocular movement, no systemic inflammatory signs at around the onset of visual loss, no additional white-matter abnormality or recurrent visual symptoms during follow-up period might support a diagnosis of optic-nerve glioma rather than optic neuritis in childhood. Other tumorous conditions such as lymphoma or inflammatory pseudotumor may be ruled in the absence of a history of painful ophthalmoplegia or a rapid deterioration of symptoms during follow-up.
Optic nerve glioma
- Hemangioma, Lymphoma, Rhabdomyosarcoma, Metastases (Neuroblastoma,
- Leukamia, Ewing’s sarcoma), Fibrous dysplasia, Paranasal mucocoele, Meningioma, Neurofibromatosis
Optic nerve and chiasm glioma
- Germinoma, Sarcoidosis
Optic chiasm glioma extending into the hypothalamus
- Pituitary adenoma, Craniopharyngioma, Malignant astrocytoma
- Dermoid cyst, Chordoma, Colloid cyst, Fibrous dyplasia, Sarcoidosis, Histiocytosis X, Tuberculous granuloma, Hemangloendothelioma
Optic glioma associated with neurofibromatosis type 1
Neurofibromatosis type 1 (NF1) is an autosomal dominantly inherited disorder with an approximate incidence of 1:4,000. Optic glioma, one of the most significant complications of NF1 in childhood, developed with an approximate prevalence of 15% (range, 1.5–24%). The period of greatest risk for the development of symptomatic optic gliomas in NF1 is during the first 6 years of life.
The treatment of optic nerve gliomas is controversial. No treatment may be required in patients with no growth, good vision & no cosmetic deformity.
In case of malignant gliomas (glioblastomas) despite treatment, including high-dose radiotherapy and chemotherapy, these tumors usually result in death within 6-12 months.
There are rare reports of spontaneous regression of optic nerve and visual pathway gliomas. Cystic enlargement of the lesions associated with sudden visual loss can occur even without true cellular growth. A treatment plan must be carefully individualized for each patient.
The following options may be considered:
- Observation only in presumed optic nerve glioma, particularly with good vision on the involved side; with careful follow up if the radiographic evidence is characteristic of this type of tumor and if the glioma is confined to the orbit. Follow-up examinations and appropriate radiographic studies, preferably MRI, must be performed at regular intervals. Many patients maintain good vision and never require surgery.
- Surgical excision in case of rapid intraorbital tumor growth to isolate the tumor from the optic chiasm and thus prevent chiasmal invasion. The surgeon should use an intracranial approach to obtain tumor-free surgical margins. Additional surgical indications may include tumors confined to the orbit with corneal exposure and compromised cosmesis unacceptable to the patient. Removal through an intracranial approach may also be indicated at the time of initial diagnosis or after a short period of observation if the tumor involves the prechiasmal intracranial portion of the optic nerve. Complete excision is possible if the tumor ends 2-3 mm anterior to the chiasm. Excision may also be required if the glioma causes an increase in intracranial pressure. Excision is rarely utilized in cases where there is residual vision.
- Radiation therapy as the sole treatment is considered if the tumor cannot be resected (usually chiasmal or optic tract lesions) and if symptoms (particularly neurological) progress. Postoperative radiation of the chiasm and optic tract may also be considered if good radiographic studies document subsequent growth of the tumor within the chiasm or if chiasmal and optic tract involvement is extensive.
- Because of debilitating side effects (including mental retardation, growth retardation, optic neuropathy or retinopathy, and secondary tumors within the radiation field), radiation is generally held as a last resort for children who have not completed growth and development.
- Combination chemotherapy using actinomycin D, vincristine, etoposide, bevacizumab and other agents has also been reported to be effective in patients with progressive chiasmal/hypothalamic gliomas. Chemotherapy may delay the need for radiation therapy and thus enhance long-term intellectual development and preservation of endocrine function in children. However, chemotherapy may also carry long-term risks of blood-borne cancers.
- Regression of optic gliomas has been reported after partial resection, chemotherapy, radiotherapy, or biopsy, and sometimes without any treatment. Other variables such as genetic, hormonal, or vascular factors seem to have more influence on tumor behavior. Most spontaneous regressions of optic glioma have been reported in those with NF1.
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