These tumors are defined as low-grade astrocytomas that occur within the optic pathways. Various components of the optic pathways can be involved: optic nerves, optic chiasm, optic tracts and/or hypothalamus. Only 10% of optic-pathway tumors are restricted to the optic nerves. Thirty percent are bilateral and more than half involve the chiasm or hypothalamus (Chapter 2, Fig. 28). Tumors involving the optic nerves present with visual loss and/or proptosis. Patients with chiasmatic/hypothalamic gliomas are usually younger than 5 years of age at diagnosis. They present with signs and symptoms of hypothalamic dysfunction, visual impairment, obstructive hydrocephalus, or an active endocrinopathy. Other signs and symptoms may include the diencephalic syndrome, diabetes insipidus, anorexia, obesity, hypersom-nia, precocious puberty, nystagmus, macrocephaly, hemiparesis and seizures. Approximately one third of patients with neurofibromatosis type 1 (NF1) will develop an optic-pathway glioma. The evaluation should include high-resolution MRI scans, a complete visual examination and an assessment of endocrine function.
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