eMedicine Specialties > Radiology > Head/Neck

Optic Nerve Glioma

Richard J Woodcock Jr, MD, Consulting Radiologist, Atlanta Radiology Consultants, LLC; Consulting Radiologist and MRI Director, St Joseph's Hospital

Updated: Jun 10, 2009

Introduction

Background

Optic nerve glioma (also known as optic pathway glioma) is the most common primary neoplasm of the optic nerve. Along with reducing visual acuity in the affected eye, the tumor sometimes produces additional symptoms as it grows. A low-grade form of this neoplasm, benign optic glioma, occurs most often in pediatric patients. Another form, aggressive glioma, is most common in adults; it is frequently fatal, even with treatment.¹

Coronal noncontrast T1-weighted MRI reveals a large intraorbital mass (arrow) centered on the optic nerve.

Axial T2-weighted MRI in a 46-year-old man demonstrates a mass in the lateral geniculate nucleus of the thalamus resulting from contiguous extension of the patient's known optic nerve glioma.

Contrasted computed tomography (CT) scanning can be used to characterize local involvement of optic nerve glioma within the orbit. However, magnetic resonance imaging (MRI) better demonstrates the extent of the lesion's intracranial growth.^2,3

Many children with optic nerve glioma are also known to have neurofibromatosis type 1 (NF-1) or, in some cases, hybrid phakomatosis.⁴

Pathophysiology

The World Health Organization classifies optic nerve gliomas as grade I astrocytomas (pilocytic astrocytomas) because they are slow growing and tend not to metastasize. Development of optic nerve gliomas occurs in stages, from generalized hyperplasia of glial cells in the nerve to complete disorganization with loss of neural landmarks in the nerve and nerve sheath. A reactive meningeal hyperplasia may be incited, making optic nerve glioma difficult to distinguish from a perioptic meningioma. It is unclear which glial cells give rise to benign optic glioma.

From 10 to 38% of pediatric patients with optic nerve glioma have NF-1; conversely, 15-40% of children with NF-1 have optic nerve glioma. Bilateral optic nerve gliomas are almost pathognomonic for NF-1.⁵

In the aggressive form of the disease, the glioma is either an anaplastic astrocytoma or a glioblastoma multiforme, arising from abnormal astrocytes. Prominent features of this neoplasm include nuclear pleomorphism, numerous mitoses, and vascular endothelial proliferation.

Frequency

United States

Optic nerve gliomas represent 4% of orbital tumors, 4% of intracranial gliomas, and 2% of intracranial tumors. They also constitute two thirds of all primary optic nerve tumors.⁶
Aggressive glioma is rare. According to Millar et al, it is an unusual presentation of a more common adult disease, astrocytoma.⁷

Mortality/Morbidity

Benign optic glioma grows relatively slowly, if at all, over extended periods. However, some lesions can progress, causing visual impairment, so ongoing follow-up has been recommended.⁸

Twenty percent of optic gliomas that extend to the optic chiasm or beyond, into the optic radiations, demonstrate a more aggressive course.

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 acuity, radiation-induced optic neuritis, and ophthalmic artery vasculopathy.

Despite aggressive radiation, chemotherapeutic, or surgical treatment, aggressive glioma is an almost uniformly fatal disease.

Race

There is no distinct racial predilection to sporadic optic nerve glioma. Benign optic glioma has the same distribution as NF-1.

Sex

In pediatric patients, there is a slight female predominance, whereas in adult patients, the opposite is true.⁶

Age

In the pediatric population, the median patient age is 5 years, with 80% of patients presenting before age 15.⁶

In adult patients, the age ranges from 22-79 years, with a mean age of 52 years.⁷

Anatomy

The optic nerve is divided into 4 parts: (1) intraocular, (2) intraorbital, (3) intracanalicular, and (4) intracranial. Within the orbit, the nerve usually is approximately 5 mm in diameter and is surrounded by fat. The intracanalicular portion passes through the lesser wing of the sphenoid and is surrounded by a muscular cone. The cerebrospinal fluid (CSF) of the subarachnoid space surrounding the nerve is contiguous with the CSF of the intracranial compartment.

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. In the absence of NF-1, the optic chiasm is most commonly involved, as is, less often, the intraorbital optic nerve.⁹ Optic nerve glioma may involve various portions of the retrobulbar visual pathway, including the optic nerve, chiasm, tracts, and radiations. Malignant lesions can invade the hypothalamus, basal ganglia, and internal capsule directly, or they may spread to the leptomeninges or subpial surfaces.

Presentation

In most young patients with optic glioma, the presenting symptom is painless proptosis. Optic atrophy is common, as is reduced visual acuity, although the latter may be a late symptom. A large lesion may compress the optic chiasm, causing nystagmus or other symptoms. 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.^10,11

In adult patients, bilateral vision loss is a common early finding because most lesions involve the optic chiasm.

Preferred Examination

When the diagnosis is in question, the presence of an intraconal mass can often be detected through CT scanning.

MRI, however, is the preferred method for definitive evaluation of optic nerve glioma. Both the intraorbital lesion and its intracranial extent can be effectively characterized through MRI. When evaluating the orbit, gadolinium-enhanced T1-weighted images with fat saturation can define the extent of aggressive glioma. Intracranially, MRI allows better evaluation of the optic nerve, chiasm, tracts, geniculate body, and optic radiations than does CT.^12,13,14

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.

NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

Limitations of Techniques

Although MRI may reveal even subtle lesions of the optic nerve, CT scanning can detect a subtle erosion or expansion 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.

Differential Diagnoses

Optic Neuritis
Retinoblastoma

Computed Tomography

Findings

In children, unenhanced CT scans typically reveal a marked, diffuse enlargement of the optic nerve, with characteristic kinking or bending. The enlargement may be tubular, fusiform, or excrescent.
Areas of lucency may result from mucinous or cystic changes.
Approximately 50% of the lesions demonstrate enhancement; this characteristic is more common with intracranial (especially retrochiasmatic) extension.
Calcifications are rare.

Degree of Confidence

The diagnosis may be made with a high degree of confidence when the lesion involves the optic chiasm and retrochiasmatic optic pathway.

When confined exclusively to the orbit, the lesion may mimic optic neuritis or optic nerve meningioma; in this setting and in most instances, MRI is a better diagnostic tool than is CT scanning.

CT scanning is the better modality for identifying uncommon meningioma with flecks of calcification, which are rare in optic nerve glioma.

False Positives/Negatives

False-positive results can occur because of unilateral optic nerve enhancement or other unilateral disorders, such as optic meningioma, vascular lesions, neuritis, pseudotumor, and sarcoidosis. In addition, subtle nerve enhancement occasionally may develop in normal individuals.

Improper examination techniques, including failure to administer contrast or obtain thin sections, can lead to a false-negative diagnosis.

Magnetic Resonance Imaging

Coronal noncontrast T1-weighted MRI reveals a large intraorbital mass (arrow) centered on the optic nerve.

Coronal postgadolinium T1-weighted MRI with fat saturation (same patient as in Image above) reveals diffuse, intense enhancement of the intraorbital mass (arrow).

Axial postgadolinium T1-weighted MRI with fat saturation (same patient as in Images above) reveals diffuse, intense enhancement of the intraorbital mass. The lesion is confined to the orbit.

Axial postgadolinium T1-weighted MRI with fat saturation in a 6-year-old girl demonstrates enhancement of the intracranial optic nerve (arrow), which is slightly expanded.

Axial noncontrast T1-weighted MRI reveals bilateral, fusiform enlargement of the optic nerves (arrows) in a 14-year-old patient with neurofibromatosis type 1, consistent with bilateral optic nerve gliomas.

Axial noncontrast T1-weighted MRI in a 46-year-old man demonstrates enlargement of both optic tracts (arrowheads) and the optic chiasm (arrow).

Axial T2-weighted MRI in a 46-year-old man demonstrates a mass in the lateral geniculate nucleus of the thalamus resulting from contiguous extension of the patient's known optic nerve glioma.