**Core Concept**
Bitemporal hemianopia is a type of visual field defect characterized by blindness in the outer half of each visual field. This condition is related to the **anatomy of the optic chiasm** and the **pathways of the visual system**. The optic chiasm is the point where the optic nerves partially cross, and lesions affecting this area can lead to specific visual field defects.

**Why the Correct Answer is Right**
The correct answer is related to a lesion affecting the optic chiasm, which is typically a **pituitary tumor**. This type of tumor can compress the optic chiasm, leading to bitemporal hemianopia. The **lateral geniculate bodies** and **optic radiations** are not typically involved in this type of visual field defect. The mechanism involves the compression of the crossing nasal fibers from each eye, which carry information from the temporal visual fields.

**Why Each Wrong Option is Incorrect**
**Option A:** Is incorrect because it does not typically cause bitemporal hemianopia.
**Option B:** Is incorrect because it is not characteristically associated with this visual field defect.
**Option D:** Is incorrect because it does not typically involve the optic chiasm.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that bitemporal hemianopia is often associated with **pituitary adenomas**, which can compress the optic chiasm. This is a critical diagnosis to consider in patients presenting with this type of visual field defect.

**Correct Answer:** C. Pituitary tumor.