Childhood visual pathway and hypothalamic gliomas are usually low-grade (grades 1 and 2) astrocytomas. Both pilocytic astrocytomas and fibrillary astrocytomas may occur. The pilomyxoid variant of pilocytic astrocytoma occurs in the visual pathway and may be a more aggressive variant and more likely to disseminate.[1] Visual pathway gliomas include astrocytic tumors of the optic nerve, optic chiasm, and optic tract. Because of the infiltrative nature of such lesions, separation of visual pathway and hypothalamic gliomas from thalamic tumors is often difficult and arbitrary. Malignant gliomas of the visual pathway are rare. Visual pathway gliomas occur at an increased incidence in patients with neurofibromatosis type 1 (NF-1); approximately 20% of all patients with NF-1 will develop a visual pathway glioma. In these patients, the tumor may be found on screening evaluations when the child is asymptomatic or has apparent static neurologic and/or visual deficits. Pathologic confirmation is frequently not obtained in asymptomatic patients, and when biopsies have been performed, these tumors have been found to be predominantly pilocytic (grade 1) rather than fibrillary (grade 2) astrocytomas.[2,3,4,5]

References:

1. Komotar RJ, Burger PC, Carson BS, et al.: Pilocytic and pilomyxoid hypothalamic/chiasmatic astrocytomas. Neurosurgery 54 (1): 72-9; discussion 79-80, 2004.
2. Kleihues P, Cavenee WK, eds.: Pathology and Genetics of Tumours of the Nervous System. Lyon, France: International Agency for Research on Cancer, 2000.
3. Listernick R, Darling C, Greenwald M, et al.: Optic pathway tumors in children: the effect of neurofibromatosis type 1 on clinical manifestations and natural history. J Pediatr 127 (5): 718-22, 1995.
4. Burger PC, Scheithauer BW: Tumors of the Central Nervous System. Washington, DC: Armed Forces Institute of Pathology,1994.
5. Allen JC: Initial management of children with hypothalamic and thalamic tumors and the modifying role of neurofibromatosis-1. Pediatr Neurosurg 32 (3): 154-62, 2000.