best delineates the tumor margins. Contrast enhancement with gadolinium can be homogenous or heterogeneous, and contrast-enhanced T1or T2-weighted images are the best for visualizing posterior extension into the tracts. In patients with NF1 there is almost always a fusiform enlargement of the optic nerve with a clear-cut margin produced by the intact dural sheath. In patients with sporadic optic nerve gliomas the nerve is more irregular and tends to show both kinking and buckling as well as low-density areas within the nerve [7].

31.1.4 Differential Diagnosis

In a patient with neurofibromatosis and optic nerve or chiasmal enlargement on MRI, the diagnosis is straightforward. However, in patients without NF1 the differential diagnosis of vision loss and optic nerve or chiasmal and hypothalamic enlargement includes malignant optic glioma of adulthood and optic nerve meningioma. In cases where there is chiasmal/hypothalamic presentation, the differential diagnosis includes chiasmal glioma, craniopharyngioma, dysgerminoma, sarcoidosis, and others.

31.1.5 Management

Because of the low incidence of OPG in the general population, its highly variable growth rate, and the variety of treatment plans proposed by different groups, optimal treatment plans are controversial. As these lesions are low grade and generally do not undergo malignant transformation and are often considered as hamartomas, some suggest that treatment of these tumors has no better outcome than the natural history of these lesions. Additionally, documented cases of tumor regression without treatment and with or without improvement in visual function occur. Therefore, treatment considerations are dependent on a number of variables including age at diagnosis, tumor location, severity of the neuroendocrine deficit, and the rate of disease progression as well as the presence or absence of NF1 [9]. When tumor is confined to the optic nerve, chiasm, or optic tracts, prognosis for life is excellent.

Anteriorly placed tumors within the orbit need to be treated if they produce unsightly proptosis, particularly if vision is significantly compromised [2]. While tumor remains confined to the optic nerve, treatment by complete surgical excision with clear margins of resection is curative. However, many of these children may retain useful vision for some time, and conservative management with close observation is reasonable. Such patients should be followed with serial MRI scans for evidence of posterior extension since visual stability or even improvement is not a reliable indicator of nonprogression.

In cases of tumor progression when surgery is not primarily indicated, the choice of therapy differs depending on if the case involves sporadic or syndromic

OPGs. Radiotherapy has been used as primary or postsurgical adjuvant therapy for both syndromic and sporadic OPGs in patients older than 5 years. However, complications were more prevalent in patients with NF1 and included cerebrovascular occlusion in a phenomenon known as moyamoya syndrome (characterized by stenosis or occlusion of the internal carotid artery and/or the proximal portion of the anterior cerebral or middle cerebral arteries, resulting in cerebral infarction and associated with radiotherapy to the brain early in life) and poorer intellectual function.

Once tumor extends to the optic chiasm the eventual threat to life from hypothalamic or third ventricle involvement rises to 28%. Surgical intervention at this point does not improve survival and is associated with significant visual morbidity and patient mortality. Similarly treatment with radiotherapy does not appear to alter the ultimate prognosis for life, but in some cases it may lead to temporary improvement in vision. However, the central nervous system complications of radiotherapy especially in very young children, should not be overlooked.

Once chiasmal tumors invade adjacent hypothalamus and/or third ventricle, the prognosis for life changes markedly with a 15-year mortality rate of more than 50%. Radiotherapy does not alter the final outcome but may possibly prolong life for several years and therefore be justified in such advanced cases. Surgical intervention is recommended only for control of hydrocephalus [7].

Chemotherapy has typically been reserved for children younger than 5 years of age requiring treatment. Chemotherapy is considered first-line therapy for OPGs that are symptomatic, such as with vision loss, pituitary dysfunction, and hypothalamic dysfunction. It can treat tumors that have gone beyond the observation age, even in young children, without the long-term cognitive and neuroendocrine sequelae seen with surgery and radiation therapy [1].

Given the data surrounding the unacceptable risks of radiotherapy in patients with NF1, chemotherapy is now regarded as the primary modality in those with progressive, nonsurgical NF1-associated OPGs. Nevertheless, such treatment carries its own risk of neuropsychological complications. The most common regimen is carboplatin/vincristine combination therapy. Other antineoplastic drugs such as temozolamide alone or lomustine are active against these tumors, but such alkylating agents have induced secondary malignancy in NF1 mouse models and thus have contraindications. The use of these agents in sporadic OPGs may be an effective alternative in individuals who cannot tolerate carboplatin and vincristine or whose tumors are resistant to them [1].

31.1.6 Prognosis

The natural history of OPGs is highly variable and is based on the anatomical location, histological findings, presence or absence of NF1, and also differences in each patient. Overall OPGs tend to be low grade and slow growing with long patient survival. The presence of NF1 and an anterior location is associated with a more