**Core Concept**
The patient presents with symptoms of visual disturbance, headache, and decreased libido, which are suggestive of a pituitary tumor affecting the hypothalamic-pituitary axis. The presence of bitemporal hemianopia points towards a suprasellar mass compressing the optic chiasm.

**Why the Correct Answer is Right**
The MRI findings likely reveal a suprasellar mass, possibly a pituitary adenoma, which is compressing the optic chiasm, leading to bitemporal hemianopia. This tumor may be secreting prolactin, leading to hyperprolactinemia, which explains the decrease in libido. The mass effect on the optic chiasm results in visual disturbances. The symptoms suggest a microadenoma, which is a small (less than 10 mm) pituitary adenoma.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not provide a clear diagnosis related to the patient's symptoms and MRI findings.
**Option B:** This option is incorrect as it does not specifically relate to the patient's symptoms and MRI findings.
**Option C:** This option is incorrect as it does not provide a clear diagnosis related to the patient's symptoms and MRI findings.

**Clinical Pearl / High-Yield Fact**
Pituitary adenomas can present with a wide range of clinical symptoms depending on their size, location, and hormonal secretions. Bitemporal hemianopia is a classic visual field defect associated with suprasellar masses compressing the optic chiasm.

**Correct Answer:** C. Pituitary Adenoma.