Optic Nerve Glioma
Optic nerve glioma is the most common primary neoplasm of the optic nerve causing decreased visual sharpness in the affected eye. Benign optic glioma occurs most often in children, more females with an average age of five years. Another form, aggressive glioma, which is unusual is most common in adults, more males with a median age of fifty-two years; it is often terminal, even with treatment. .
From 10-38% of children with optic nerve glioma is also known to have neurofibromatosis type 1 (NF-1) or, in some cases, the more recently described hybrid phakomatosis. In 66% of NF-1 patients with optic nerve glioma, the growth involves the intraorbital optic nerve. In 10-20%, the tumor is confined to the orbit, with the remainder of these patients showing involvement of the intracranial compartment.
Optic nerve gliomas represent 4% of orbital tumors, 4% of intracranial gliomas, and 2% of intracranial tumors. They also include two thirds of all primary optic nerve tumors.
Benign optic glioma develops gradually, if at all. Yet, some lesions can grow, causing visual impairment, so follow-up is recommended.
Twenty percent of optic gliomas that extend to the optic chiasm or outside, into the optic radiations, exhibit a more aggressive path.
In the absence of NF-1, the optic chiasm is most usually involved, as is, less often, the intraorbital optic nerve. Optic nerve glioma may involve different sections of the retrobulbar visual pathway, including the optic nerve, chiasm, tracts, and radiations. Malignant lesions can occupy the hypothalamus, basal ganglia, and internal capsule directly, or they may extend to the leptomeninges or subpial surfaces.
In most young patients with optic glioma, the symptom is painless proptosis. Optic atrophy is common, as is reduced visual sharpness, (which may be a late symptom). A large lesion may compress the optic chiasm, causing nystagmus. Hypothalamic symptoms, such as changes in appetite or sleep, also may occur. Massive lesions may compress the third ventricle, resulting in obstructive hydrocephalus accompanied by headache, nausea, and vomiting.
In adult patients, bilateral vision loss is a common early finding because most lesions involve the optic chiasm.
Contrasted computed tomography (CT) scanning can be used to differentiate confined involvement of optic nerve glioma within the orbit and the presence of an intraconal mass. CT scanning can distinguish a faint attrition or growth of the optic canal. In addition, fine calcification, which may help to identify a lesion as a meningioma rather than a glioma, is visualized best through CT scanning.
Findings:
In children, unenhanced CT scans normally reveal an evident, diffuse growth of the optic nerve, with typical twisting. The enlargement may be tubular, fusiform, or excrescent.
Areas of lucency may result from mucinous or cystic changes.
Approximately 50% of the lesions reveal enhancement; this characteristic is more common with intracranial (especially retrochiasmatic) extension.
Calcifications are unusual.
Improper examination techniques, including failure to administer contrast or obtain thin sections, can lead to a false-negative diagnosis.
Magnetic Resonance Imaging (MRI), however, is the preferred method for definitive evaluation of optic nerve glioma. Both the intraorbital lesion and its intracranial degree can be effectively differentiated through MRI. When evaluating the orbit, gadolinium-enhanced T1-weighted images with fat saturation can define the degree of aggressive glioma. Intracranially, MRI allows better evaluation of the optic nerve, chiasm, tracts, geniculate body, and optic radiations and shows even slight lesions of the optic nerve than does CT.
Findings:
On T1-weighted images, optic nerve gliomas are usually isointense to the cortex and hypointense to white matter.
Invariably, the lesions are hypointense to orbital fat.
On T2-weighted images, lesions show a varied appearance that is isointense to hyperintense relative to white matter and the cortex.
Following contrast administration, intense enhancement is common.
A diagnosis of NF-1 may be supported by several findings including the following:
Bilateral optic nerve gliomas.
Spongiform changes (hyperintensity on T2-weighted images) in the cerebellum, brain stem, basal ganglia, thalamus, periventricular white matter, and corpus callosum
Adult lesions may involve the orbital, intracanalicular, or prechiasmal portions of the optic nerve, resulting in enlargement; they may exhibit retrochiasmatic extension as well).
Usually, the lesions are hypointense to isointense relative to the optic nerve on T1-weighted images and are hyperintense to it on T2-weighted images. Enhancement is homogeneous and intense.
Patients without NF-1 show cystic components more commonly at T2 -weighted imaging.
The diagnosis may be made with a high level of confidence when the lesion involves the optic chiasm and retrochiasmatic optic pathway.
When limited entirely to the orbit, the lesion may imitate optic neuritis, pseudotumor, lymphoma, or optic nerve meningioma. Characteristically, meningioma, the main differential diagnostic consideration, is distinguished by the "tram-track" sign, with enhancement of the periphery of the nerve–optic sheath unit. Conversely, enhancement in optic nerve glioma is more uniform. Isolated growth of the optic nerve sheath also may present diagnostic complexity; however, this enlargement can generally be distinguished by its signal characteristics, which follow fluid signal on all MRI pulse sequences.
In most occasions, the diagnosis can be made with greater assurance using MRI than it can with CT scanning.
A false-positive diagnosis can occur as an effect of unilateral optic nerve enhancement or other unilateral disorders, such as optic meningioma, vascular lesions, neuritis, pseudotumor, lymphoma, and sarcoidosis. In addition, subtle nerve enhancement occasionally may develop in normal individuals.
Improper examination procedures, including failure to administer contrast, use fat saturation, or obtain thin sections, can result in a false-negative diagnosis.
Local surgical therapy for large lesions may cause significant morbidity, including hypothalamic dysfunction. Stereotactic radiation or gamma-knife therapy also can produce complications, including decreased visual perception, radiation-induced optic neuritis, and ophthalmic artery vasculopathy.
Despite aggressive radiation, chemotherapeutic, or surgical treatment, aggressive glioma is an almost uniformly fatal disease.
Information By: Emory University School of Medicine.org
Optic nerve glioma is the most common primary neoplasm of the optic nerve causing decreased visual sharpness in the affected eye. Benign optic glioma occurs most often in children, more females with an average age of five years. Another form, aggressive glioma, which is unusual is most common in adults, more males with a median age of fifty-two years; it is often terminal, even with treatment. .
From 10-38% of children with optic nerve glioma is also known to have neurofibromatosis type 1 (NF-1) or, in some cases, the more recently described hybrid phakomatosis. In 66% of NF-1 patients with optic nerve glioma, the growth involves the intraorbital optic nerve. In 10-20%, the tumor is confined to the orbit, with the remainder of these patients showing involvement of the intracranial compartment.
Optic nerve gliomas represent 4% of orbital tumors, 4% of intracranial gliomas, and 2% of intracranial tumors. They also include two thirds of all primary optic nerve tumors.
Benign optic glioma develops gradually, if at all. Yet, some lesions can grow, causing visual impairment, so follow-up is recommended.
Twenty percent of optic gliomas that extend to the optic chiasm or outside, into the optic radiations, exhibit a more aggressive path.
In the absence of NF-1, the optic chiasm is most usually involved, as is, less often, the intraorbital optic nerve. Optic nerve glioma may involve different sections of the retrobulbar visual pathway, including the optic nerve, chiasm, tracts, and radiations. Malignant lesions can occupy the hypothalamus, basal ganglia, and internal capsule directly, or they may extend to the leptomeninges or subpial surfaces.
In most young patients with optic glioma, the symptom is painless proptosis. Optic atrophy is common, as is reduced visual sharpness, (which may be a late symptom). A large lesion may compress the optic chiasm, causing nystagmus. Hypothalamic symptoms, such as changes in appetite or sleep, also may occur. Massive lesions may compress the third ventricle, resulting in obstructive hydrocephalus accompanied by headache, nausea, and vomiting.
In adult patients, bilateral vision loss is a common early finding because most lesions involve the optic chiasm.
Contrasted computed tomography (CT) scanning can be used to differentiate confined involvement of optic nerve glioma within the orbit and the presence of an intraconal mass. CT scanning can distinguish a faint attrition or growth of the optic canal. In addition, fine calcification, which may help to identify a lesion as a meningioma rather than a glioma, is visualized best through CT scanning.
Findings:
In children, unenhanced CT scans normally reveal an evident, diffuse growth of the optic nerve, with typical twisting. The enlargement may be tubular, fusiform, or excrescent.
Areas of lucency may result from mucinous or cystic changes.
Approximately 50% of the lesions reveal enhancement; this characteristic is more common with intracranial (especially retrochiasmatic) extension.
Calcifications are unusual.
Improper examination techniques, including failure to administer contrast or obtain thin sections, can lead to a false-negative diagnosis.
Magnetic Resonance Imaging (MRI), however, is the preferred method for definitive evaluation of optic nerve glioma. Both the intraorbital lesion and its intracranial degree can be effectively differentiated through MRI. When evaluating the orbit, gadolinium-enhanced T1-weighted images with fat saturation can define the degree of aggressive glioma. Intracranially, MRI allows better evaluation of the optic nerve, chiasm, tracts, geniculate body, and optic radiations and shows even slight lesions of the optic nerve than does CT.
Findings:
On T1-weighted images, optic nerve gliomas are usually isointense to the cortex and hypointense to white matter.
Invariably, the lesions are hypointense to orbital fat.
On T2-weighted images, lesions show a varied appearance that is isointense to hyperintense relative to white matter and the cortex.
Following contrast administration, intense enhancement is common.
A diagnosis of NF-1 may be supported by several findings including the following:
Bilateral optic nerve gliomas.
Spongiform changes (hyperintensity on T2-weighted images) in the cerebellum, brain stem, basal ganglia, thalamus, periventricular white matter, and corpus callosum
Adult lesions may involve the orbital, intracanalicular, or prechiasmal portions of the optic nerve, resulting in enlargement; they may exhibit retrochiasmatic extension as well).
Usually, the lesions are hypointense to isointense relative to the optic nerve on T1-weighted images and are hyperintense to it on T2-weighted images. Enhancement is homogeneous and intense.
Patients without NF-1 show cystic components more commonly at T2 -weighted imaging.
The diagnosis may be made with a high level of confidence when the lesion involves the optic chiasm and retrochiasmatic optic pathway.
When limited entirely to the orbit, the lesion may imitate optic neuritis, pseudotumor, lymphoma, or optic nerve meningioma. Characteristically, meningioma, the main differential diagnostic consideration, is distinguished by the "tram-track" sign, with enhancement of the periphery of the nerve–optic sheath unit. Conversely, enhancement in optic nerve glioma is more uniform. Isolated growth of the optic nerve sheath also may present diagnostic complexity; however, this enlargement can generally be distinguished by its signal characteristics, which follow fluid signal on all MRI pulse sequences.
In most occasions, the diagnosis can be made with greater assurance using MRI than it can with CT scanning.
A false-positive diagnosis can occur as an effect of unilateral optic nerve enhancement or other unilateral disorders, such as optic meningioma, vascular lesions, neuritis, pseudotumor, lymphoma, and sarcoidosis. In addition, subtle nerve enhancement occasionally may develop in normal individuals.
Improper examination procedures, including failure to administer contrast, use fat saturation, or obtain thin sections, can result in a false-negative diagnosis.
Local surgical therapy for large lesions may cause significant morbidity, including hypothalamic dysfunction. Stereotactic radiation or gamma-knife therapy also can produce complications, including decreased visual perception, radiation-induced optic neuritis, and ophthalmic artery vasculopathy.
Despite aggressive radiation, chemotherapeutic, or surgical treatment, aggressive glioma is an almost uniformly fatal disease.
Information By: Emory University School of Medicine.org
