Figures 1 and 2: Axial FLAIR images demonstrate expansion of the optic chiasm and the contiguous
intracranial optic nerves and left intra-orbital optic nerves. There is signal abnormality coursing posteriorly through the deep white matter tracts and into the left periventricular white matter.
Signal abnormality can also be seen in the lentiform nucleus.

Movie 1: Coronal T2-weighted STIR images again demonstrate an enlarged optic chiasm and signal
abnormalities extending posteriorly through the deep white matter tracts and into the left periventricular white matter.

Optic glioma.

Neurofibromatosis (NF) is one of the phakomatoses or congenital neuroectodermal dysplasias. It consists of several distinct diseases including Neurofibromatosis Type I (NF-1;Von Recklinhausen disease) and Neurofibromatosis Type II (NF-2: central neurofibromatosis). NF-1 is an autosomal dominant disease associated with a defect in chromosome number 17. It has an incidence of one in three to four thousand births. Expressivity is variable and the spontaneous mutation rate is 50%. Criteria for diagnosing NF-1 are met if an individual has 2 or more of the following:

1. Six or more café au lait spots (5 mm greatest diameter pre-pubertal or 15 mm post-pubertal)
2. Two or more neurofibromas or one plexiform neurofibroma
3. Freckling in the axillary or inguinal regions
4. Optic glioma (The most common CNS manifestation of NF-1)
5. Two or more Lisch nodules
6. Distinctive osseous lesions such as sphenoid dysplasia, anterior tibial bowing or pseudoarthrosis
7. First degree relative with NF-1 by the above criteria

Other than optic glioma additional intracranial abnormalities can include hydrocephalus, occlusions or stenoses of the proximal cerebral vasculature, sphenoid wing dysplasia with secondary herniation of the temporal lobe into the orbit and pulsatile exophthalmos, and plexiform craniofacial neurofibromas involving the cavernous sinus, orbit, or facial soft tissues.

Optic glioma (grade I astrocytoma) is the most common primary neoplasm of the optic nerve. Optic glioma represents approximately 5% of all brain tumors and 10-15% of all supratentorial tumors in children . It can be divided into the two groups: benign optic glioma in children and aggressive glioma in adults. In most cases, optic gliomas arise in children with a typical age of diagnosis between two and six years of age (median age of 5 years) with 75-80% of patients presenting before age 15. These lesions have a slight female predominance. Of pediatric patients with optic glioma, 10-38% have NF-1, while 15-40% of children with NF-1 have optic glioma. Bilateral optic gliomas are virtually pathognomonic for Neurofibromatosis type I.

In the pediatric form of the disease the cell of origin for optic gliomas is unknown. Optic gliomas are generally well-differentiated, low grade, slow growing astrocytomas, which can infiltrate along the optic tracts or nerves. They do not tend to metastasize. Ten to twenty percent of optic pathway gliomas are confined to the orbit either unilaterally or bilaterally, however, these lesions can arise anywhere along the optic pathway including the optic nerve, optic chiasm, optic tracts, optic radiation, and occipital cortex. In the case of optic gliomas that extend to the optic chiasm, 20% of patients demonstrate a more aggressive course. When malignant, optic gliomas may extend to invade the hypothalamus, basal ganglia, and internal capsule directly, or they my spread to the leptomeninges or subpial surfaces.

In most pediatric patients with optic glioma the presenting symptoms include painless proptosis and progressive, nonpulsatile exopthalmus with decreased eye movement and optic atrophy. However depending on size of the lesion other symptoms can include reduction in visual acuity, which can be unilateral or bilateral and is common but late symptom; nystagmus; hypothalamic symptoms (e.g. change in sleep or appetite); headache, nausea, and vomiting associated with obstructive hydrocephalus; and neurologic deficits.

MRI is the preferred method for evaluating optic gliomas. MR images allow for effective characterization of both the intraorbital lesions and clearly shows the intracanalicular and prechiasmatic intracranial nerve without artifact from nearby bony structures. MR is also ideal for demonstrating intracranial extension (optic nerve, chiasm, tracts, geniculate body and optic radiations). MR imaging generally demonstrates the optic glioma lesions to be isointense to the cortex and hypointense to white matter on T1-weighted images. On T2-weighted images optic gliomas demonstrate a hyperintense appearance to white matter and cortex. On post-contrast images, enhancement is variable, but usually moderate to marked.

There are no specific clinical, histologic, or neuroimaging features to differentiate aggressive from indolent optic gliomas. However, the prognosis is reportedly much better in children with optic gliomas and NF than those with optic gliomas without NF. Treatment consists of surgery, chemotherapy, and irradiation. Local therapy for large lesions with surgery may result in significant morbidity, including hypothalamic dysfunction.

References:

1. Atlas, Scott W. Magnetic Resonance Imaging of the Brain and Spine, 3rd Ed. Philadelphia: Lippincott Williams & Wilkins, c2002. pp. 1043-1046.
2. Hollander MD, FitzPatrick M, O’Connor SG, et al. Optic Gliomas. Radiologic Clinics of North America. 1999; 11(4): 749-54.
3. Kornreich L, Blaser S, Schwarz, et al. Optic Pathway Glioma: Correlation of Imaging Findings with the Presence of Neurofibromatosis. American Journal of Neuroradiology. 2001; 22: 1963-1969.
4. Chateil J-F, Soussotte C, et al. MRI and Clinical Differences Between Optic Pathway Tumors in Children With and Without Neurofibromatosis. The British Journal of Radiology. 2001; 74: 24-31.