**Core Concept**
Pituitary macroadenomas are benign tumors arising from the pituitary gland that can cause visual disturbances, hormonal imbalances, and other systemic symptoms due to their proximity to critical structures in the sellar region.

**Why the Correct Answer is Right**
The patient's presentation of menstrual irregularity, galactorrhoea, and bitemporal superior quadrantanopia is highly suggestive of a pituitary macroadenoma. These tumors can secrete prolactin, leading to galactorrhoea and menstrual irregularities. The bitemporal superior quadrantanopia is due to compression of the optic chiasm by the tumor, which is a characteristic feature of pituitary macroadenomas. The primary optic atrophy on fundus examination further supports this diagnosis, as prolonged compression of the optic nerves can lead to atrophy.

**Why Each Wrong Option is Incorrect**
**Option A:** Craniopharyngiomas are rare, benign tumors that arise from the remnants of the Rathke's pouch and can cause visual disturbances, hormonal imbalances, and other systemic symptoms. However, they are more common in children and are typically associated with calcifications on imaging.

**Option C:** Ophthalmic ICA aneurysms are a type of cerebral aneurysm that can cause visual disturbances, but they are more commonly associated with sudden, severe vision loss rather than gradual symptoms. Additionally, they are not typically associated with menstrual irregularities or galactorrhoea.

**Option D:** Chiasmal gliomas are rare, slow-growing tumors that arise from the optic chiasm and can cause visual disturbances. However, they are more common in children and are typically associated with a more rapid progression of symptoms.

**Clinical Pearl / High-Yield Fact**
Pituitary macroadenomas are the most common type of pituitary tumor, and they can cause a wide range of systemic symptoms due to their proximity to critical structures in the sellar region. A high index of suspicion is necessary for early diagnosis, as delayed treatment can lead to irreversible visual loss and other complications.

✓ Correct Answer: B. Pituitary macroadenoma