**Core Concept**
Optic nerve sheath meningioma is a type of tumor that arises from the meninges surrounding the optic nerve. It is a slow-growing neoplasm that can compress the optic nerve, leading to visual disturbances and other symptoms.

**Why the Correct Answer is Right**
The ophthalmoscopic sign pathognomonic of optic nerve sheath meningioma is the "sausage-like" or "doughnut-like" appearance of the optic disc. This is due to the compression of the optic nerve by the tumor, which causes the nerve to appear swollen and constricted. The characteristic appearance is often described as a "meniscus sign" or "meniscus shape," where the optic disc appears as a crescent-shaped structure. This sign is specific to optic nerve sheath meningioma and is not typically seen in other conditions that affect the optic nerve.

**Why Each Wrong Option is Incorrect**
**Option A:** This is not a specific ophthalmoscopic sign associated with optic nerve sheath meningioma. While it may be a feature of other conditions, it is not pathognomonic for this particular tumor.
**Option B:** This is a feature of papilledema, which is a different condition altogether. Papilledema is characterized by swelling of the optic disc due to increased intracranial pressure, but it does not have the same "sausage-like" appearance as optic nerve sheath meningioma.

**Clinical Pearl / High-Yield Fact**
When examining patients with suspected optic nerve sheath meningioma, look for the characteristic "sausage-like" appearance of the optic disc, which is a key diagnostic feature of this condition. This sign can help differentiate optic nerve sheath meningioma from other conditions that affect the optic nerve.

**Correct Answer:** C.