**Core Concept**
The most common intracranial tumor to extend into the orbit is a meningioma arising from the sphenoidal wing of the sphenoid bone, which forms a direct anatomical bridge between the cranial cavity and the orbital cavity.

**Why the Correct Answer is Right**
Sphenoidal wing meningiomas originate from the dura mater of the sphenoid sinus and extend into the orbit through the orbital floor, particularly via the inferior orbital fissure. These tumors are benign, slow-growing, and frequently present with proptosis, diplopia, and visual disturbances due to their location. They are the most common intracranial tumor to directly invade or extend into the orbit, especially in adults over 40 years. Their proximity to the orbital floor and the presence of a dural sheath allow for direct orbital infiltration.

**Why Each Wrong Option is Incorrect**
Option A: Astrocytomas are intracranial gliomas that rarely extend into the orbit and usually grow within the brain parenchyma. They are not known for orbital extension.
Option B: Pituitary adenomas are typically confined to the sella turcica and may cause visual field defects due to optic chiasm compression, but they rarely extend into the orbit.
Option C: Craniopharyngiomas are located in the suprasellar region and may compress the optic chiasm, but they do not commonly extend into the orbit.

**Clinical Pearl / High-Yield Fact**
Meningiomas, especially those from the sphenoidal wing, are the most common cause of orbital extension from intracranial tumors. Always consider this when a patient presents with proptosis and cranial nerve palsies without a history of trauma or metastasis.

✓ Correct Answer: D. Sphenoidal wing meningioma