Optic Nerve, Chiasmal, and Hypothalamic Tumors

Gliomas are the most common tumors in the optic nerve, chiasmal, and hypothalamic regions of the central nervous system (CNS). As such, they are the focus of this chapter. For completeness, the less common tumors of these regions—meningiomas and craniopharyngiomas—are also covered. Germ cell tumors can also occur in this region but are discussed in Chapter 7. GLIOMAS Gliomas that affect the optic nerves, chiasm, and hy-pothalamus represent a unique type of tumor with a variable clinical course. Histologically, most other midline astrocytomas of childhood are of the pilo-cytic subtype. These gliomas are among the neo-plasms of the nervous system whose tumor type and prognosis are age related. Except for infants, the prognosis for patients with these tumors is inversely related to age at onset, with older individuals having a poorer prognosis. In infancy, tumors affecting the optic pathways can be malignant in their course, although the reasons for this are not known. Gliomas of the optic nerves and chiasm are strongly associated with neurofibromatosis type 1. Several large series report obvious signs of neurofibromatosis in as many as 54% of affected children Gliomas affecting the hypothalamus and anterior third ventricle are also strongly associated with neurofi-bromatosis and may be found in tuberous sclerosis, another hereditary condition. The pathology of optic pathway gliomas runs the gamut from very benign astrocytomas, considered by some to be hamartomas, to tumors that are glioblas-toma multiforme. The typical histologic picture of a glioma of the optic nerve is one of dense arachnoid proliferation around an infiltrating pilocytic glioma, with thin hair-like tumor cells intermixed among the fibers of the optic nerve itself. The low-grade gliomas that tend to affect the optic chiasm, anterior third ven-tricle, and hypothalamus frequently are characterized as juvenile pilocytic astrocytomas, having few mitoses, no malignant features, or degenerative changes such as Rosenthal fibers. Despite their relatively " benign " histology, these tumors can progress and cause considerable morbidity in young children. Occasionally, anterior third ventricle tumors are discovered in conjunction with tuberous sclerosis; these tumors are generally noninfiltrating, relatively benign subependy-mal giant cell astrocytoma (see Chapter 3). Overall, approximately 4% to 5% of optic pathway tumors are frankly malignant, and those usually have many of the characteristics typical of glioblastoma multiforme. The tumors with malignant histology occur most commonly in adolescents and older individuals. In addition to patient age, anatomic distinctions are extremely important in the evolution and prognosis of …