Tumors may affect the ONH (eg, melanocytoma, peripapillary choroidal melanoma, choroidal osteoma, and hemangioma) or the retrobulbar portion of the optic nerve (eg, glioma and meningioma). Invasion of the optic nerve can occur through direct extension of orbital or CNS tumors (eg, leptomeningeal carcinomatosis). Direct infiltration of the optic nerve may occur in hematologic malignancies (eg, leukemia). See BCSC Section 5, Neuro-Ophthalmology, and Section 7, Oculofacial Plastic and Orbital Surgery, for more information on these entities. The discussion in the following sections focuses on the histologic features of the more common optic nerve neoplasms.
Melanocytoma of the ONH is a benign, heavily pigmented (dark-brown to jet-black) melanocytic tumor located eccentrically on the ONH and adjacent choroid (Fig 15-12A; see also Chapter 17). It may be elevated and extend into the adjacent retina or extend posteriorly into the optic nerve. Melanocytomas may grow slowly, but malignant transformation to melanoma is rare. Histologically, melanocytoma is a magnocellular nevus, composed of closely packed, heavily pigmented, plump polyhedral melanocytes. The dense pigment obscures nuclear detail (Fig 15-12B, C), so melanin bleach preparations (Fig 15-12D) are necessary to reveal the bland cytologic features, such as abundant cytoplasm, small nuclei with finely dispersed chromatin, and inconspicuous nucleoli. Necrosis and histiocytic infiltration are sometimes observed within melanocytoma and are not necessarily indicative of aggressive behavior. See also Chapters 12 and 17.
Figure 15-12 Melanocytoma of the optic nerve. A, Fundus photograph shows a dark mass on the inferior edge of the ONH. B, Low-magnification photomicrograph of melanocytoma shows a dome-shaped, jet-black mass involving the prelaminar optic nerve. The tumor also involves the juxtapapillary choroid and retina. C, Higher magnification shows darkly pigmented polyhedral melanocytes with dense intracytoplasmic pigment obscuring nuclear detail. D, Melanin bleach preparation shows the bland nuclear morphology and abundant cytoplasm of melanocytoma cells. Note the area of necrosis within the tumor (arrow).
(Part A courtesy of Robert H. Rosa Jr, MD; parts B–D courtesy of Tatyana Milman, MD.)
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.