Which of the following is an orbital lesion (not intrinsic to the optic nerve)?

• A. Optic nerve glioma
• B. Optic nerve sheath meningioma
• C. Orbital cavernous hemangioma
• D. Melanocytoma

Answer: (C)

This item tests your ability to distinguish tumors that originate from the optic nerve itself from those that lie in the orbit but do not arise from the nerve tissue. An orbital cavernous hemangioma is a benign vascular tumor that develops within the orbit, typically in the intraconal space and away from the nerve itself. It grows slowly and tends to compress the optic nerve from the outside rather than arising from or replacing nerve tissue, so it is considered not intrinsic to the optic nerve.

In contrast, an optic nerve glioma starts inside the nerve itself, arising from glial cells and causing intrinsic enlargement of the nerve. Melanocytoma involves pigmented cells of the optic nerve head, making it intrinsic to the nerve structure. Optic nerve sheath meningioma arises from the meninges around the optic nerve (the sheath), forming a lesion adjacent to or around the nerve, but not from the nerve substance itself.

Thus, the orbital cavernous hemangioma fits best as an orbital lesion not intrinsic to the optic nerve.