**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. This condition is typically caused by a lesion affecting the optic chiasm, which is the location where the optic nerves from each eye cross over.

**Why the Correct Answer is Right**
The optic chiasm is a critical structure in the visual pathway where the optic nerves from each eye cross over, allowing for binocular vision. A lesion in this area can compress or damage the crossing optic nerve fibers, leading to bitemporal hemianopia. This type of lesion often involves the pituitary gland or a pituitary adenoma, which can compress the optic chiasm from below.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because lesions in the optic nerve or optic tract would result in different types of visual field defects, such as unilateral visual loss or homonymous hemianopia.

**Option B:** This option is incorrect because lesions in the occipital lobe would result in visual field defects such as quadrantanopia or homonymous hemianopia.

**Option C:** This option is incorrect because lesions in the optic radiations would result in visual field defects such as quadrantanopia or homonymous hemianopia.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of bitemporal hemianopia is the presence of a central scotoma, which is a small area of vision loss in the center of the visual field. This is due to the compression of the optic chiasm fibers that carry information from the central retina.

**Correct Answer: C. Optic chiasm.