**Core Concept**
Prolactinomas are a type of pituitary adenoma that secrete excess prolactin, leading to various endocrine disorders. The patient's presentation of secondary amenorrhea and galactorrhea suggests hyperprolactinemia, which is often caused by a prolactin-secreting tumor.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with hyperprolactinemia, which is characterized by elevated levels of prolactin in the blood. Prolactinomas are the most common cause of hyperprolactinemia, and they often present with symptoms such as galactorrhea, amenorrhea, and infertility. The pituitary gland produces prolactin, and an overproduction of this hormone can disrupt the normal function of the hypothalamic-pituitary-gonadal axis, leading to the patient's symptoms. The prolactinoma can be a microadenoma (less than 10 mm in diameter) or a macroadenoma (larger than 10 mm in diameter).

**Why Each Wrong Option is Incorrect**
**Option A:** Craniopharyngioma is a type of brain tumor that occurs in the suprasellar region, which can cause visual disturbances, endocrine dysfunction, and other symptoms. However, it is not typically associated with hyperprolactinemia.
**Option C:** Meningioma is a type of tumor that arises from the meninges, the protective membranes surrounding the brain and spinal cord. While it can cause a variety of symptoms, including endocrine dysfunction, it is not typically associated with hyperprolactinemia.
**Option D:** Sub-arachnoid hemorrhage is a type of bleeding that occurs in the space surrounding the brain, and it can cause a variety of symptoms, including headache, nausea, and vomiting. However, it is not typically associated with hyperprolactinemia.

**Clinical Pearl / High-Yield Fact**
A prolactinoma can be treated with dopamine agonists, such as bromocriptine or cabergoline, which can help reduce prolactin levels and alleviate symptoms. It is essential to diagnose and treat prolactinomas promptly to prevent long-term consequences, such as infertility and osteoporosis.

**✓ Correct Answer:** B. **Prolactinoma**