**Core Concept**
Intracranial tumors extending to the orbit are a type of complication that can arise from various primary brain tumors. The most common types of intracranial tumors are gliomas, meningiomas, and pituitary adenomas. When these tumors grow and extend into the orbit, they can cause a range of symptoms including proptosis, vision loss, and diplopia.

**Why the Correct Answer is Right**
The most common intracranial tumor that extends to the orbit is a meningioma. Meningiomas arise from the meninges, the protective membranes surrounding the brain and spinal cord. They are often slow-growing and can cause a range of symptoms depending on their location. When a meningioma extends into the orbit, it can compress or invade orbital structures, leading to proptosis and vision loss. The orbital extension of a meningioma is often due to the tumor's tendency to grow along the dural surfaces and the orbital apex, where it can compress the optic nerve and other critical structures.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a common type of intracranial tumor that extends to the orbit. While gliomas are common intracranial tumors, they are less likely to extend to the orbit compared to meningiomas.
* **Option B:** This option is a type of tumor, but it is not the most common type to extend to the orbit. Pituitary adenomas are more likely to cause symptoms related to hormonal imbalances rather than orbital extension.
* **Option C:** This option is not a type of tumor at all, but rather a symptom of orbital extension. While proptosis is a common symptom of orbital extension, it is not a type of tumor.

**Clinical Pearl / High-Yield Fact**
The key to diagnosing orbital extension of a meningioma is to look for symptoms such as proptosis, vision loss, and diplopia in a patient with a known meningioma. A thorough ophthalmological examination and imaging studies such as CT or MRI are essential for confirming the diagnosis.

**Correct Answer: A. Meningioma**