**Core Concept**
Bitemporal hemianopia is a type of visual field defect characterized by the loss of vision in the outer half of each visual field, resulting from damage to the optic chiasm. This condition occurs due to the compression or destruction of the optic chiasm by a lesion, leading to the interruption of the crossing nasal fibers.

**Why the Correct Answer is Right**
The correct answer is a condition that compresses or destroys the optic chiasm, resulting in the interruption of the crossing nasal fibers. This compression can be caused by a pituitary adenoma, which is a benign tumor that arises from the pituitary gland. The pituitary gland is located near the optic chiasm, and as it grows, it can compress the optic chiasm, leading to bitemporal hemianopia. The optic chiasm contains the crossing nasal fibers from each eye, which carry information from the temporal fields of each eye.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the optic chiasm or the compression of the nasal fibers. It is a distractor and does not accurately describe a condition that would result in bitemporal hemianopia.

**Option B:** This option might seem plausible, but it is not the correct answer. While lesions in the optic nerve can result in visual field defects, they do not typically cause bitemporal hemianopia.

**Option D:** This option is also not the correct answer. While lesions in the occipital lobe can result in visual field defects, they do not typically cause bitemporal hemianopia.

**Clinical Pearl / High-Yield Fact**
A classic exam trap is to remember that lesions compressing the optic chiasm typically result in bitemporal hemianopia, while lesions compressing the optic nerves typically result in monocular visual field defects.

**Correct Answer:** C. A pituitary adenoma compressing the optic chiasm.