A glioma (astrocytoma) may arise in any part of the visual pathway, including the ONH and optic nerve. Optic nerve gliomas are frequently associated with neurofibromatosis 1 (NF1). The tumors are low-grade juvenile pilocytic astrocytomas and commonly present in the first decade of life. Histologic examination of juvenile pilocytic astrocytoma shows proliferation of spindle-shaped astrocytes with delicate, hairlike (pilocytic) cytoplasmic processes that expand the optic nerve parenchyma (Fig 15-13). Enlarged, strongly eosinophilic filaments, known as Rosenthal fibers, may be found in these tumors and represent degenerating cell processes (see Fig 15-13C). In addition, calcification and foci of microcystoid degeneration can be seen; the pial septa may be thickened. The meninges show reactive hyperplasia and astrocyte infiltration. Because the dura remains intact, the nerve exhibits fusiform or sausage-shaped enlargement within the sheath.
Figure 15-13 Astrocytoma of the optic nerve. A, The right side of this photomicrograph demonstrates a normal optic nerve (asterisk); the left side shows a pilocytic astrocytoma, which is more cellular in appearance. B, The neoplastic glial cells are elongated to resemble hairs (hence the term pilocytic). C, Degenerating eosinophilic filaments, known as Rosenthal fibers (arrows), may be observed in these tumors.
High-grade tumors (grade IV astrocytomas, also known as glioblastoma multiforme) rarely involve the optic nerve; when involvement of the optic nerve does occur, it usually is due to a primary brain tumor. Primary malignant glioma of the anterior visual pathway is rare and occurs mainly in adults. It is characterized histologically by nuclear pleomorphism, high mitotic activity, necrosis, and hemorrhage.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.