Primary malignant melanoma of the optic nerve simulating a melanocytoma

Primary malignant melanoma of the optic nerve head is an extremely rare tumor. We describe a patient with a pigmented optic nerve lesion that simulated a growing melanocytoma. The pigmented tumor slowly infiltrated the optic nerve causing disc edema, retinal venous congestion, progressive visual field loss, and eventually, loss of central acuity. Following enucleation of the eye, and later resections of the optic nerve to the chiasm, histopathologic examination of the optic nerve, disc, and peripapillary region demonstrated a primary malignant melanoma of the optic nerve without choroidal involvement. Involvement of the optic nerve extended 26 mm beyond the lamina cribrosa. Malignant melanoma of the optic nerve is a real entity and may clinically simulate a melanocytoma.