Large pituitary tumour results in
**Core Concept**
A large pituitary tumour can lead to increased intracranial pressure and subsequent damage to surrounding brain structures. This is due to the tumour's mass effect, which is a common complication of pituitary macroadenomas. The sella turcica, a saddle-shaped structure, houses the pituitary gland and provides a confined space for the gland's expansion.
**Why the Correct Answer is Right**
In a large pituitary tumour, the mass effect can lead to the compression of the optic chiasm, resulting in bitemporal hemianopia. The optic chiasm is a critical structure that transmits visual information from the nasal halves of each retina to the contralateral visual cortex. Compression of the optic chiasm by the pituitary tumour can disrupt this transmission, causing visual field defects. The pituitary gland is also located close to the hypothalamus, and large tumours can disrupt the delicate balance of the hypothalamic-pituitary-adrenal axis, leading to hormonal imbalances.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while a large pituitary tumour can lead to increased intracranial pressure, it is not the most direct consequence of a pituitary tumour.
* **Option B:** This option is incorrect because while a pituitary tumour can disrupt the hypothalamic-pituitary-adrenal axis, it is not the most common consequence of a large pituitary tumour.
**Clinical Pearl / High-Yield Fact**
The Bimodal distribution of pituitary tumours is a classic exam trap: most pituitary tumours are microadenomas (10mm) are more likely to cause mass effects and compress surrounding structures.
**Correct Answer:** D.