Visual field defect in pituitary tumour with suprasellar extension is:
**Core Concept**
A visual field defect in a pituitary tumor with suprasellar extension is related to the compression of the optic chiasm, which is a critical structure in the visual pathway. The optic chiasm is formed by the crossing of optic nerve fibers from both eyes, and compression here can lead to characteristic visual field defects.
**Why the Correct Answer is Right**
The correct answer is a bitemporal hemianopia. This type of visual field defect occurs due to the compression of the optic chiasm, where the fibers from the nasal halves of each retina are affected. This leads to a loss of vision in the outer (temporal) fields of both eyes. The compression of the optic chiasm can cause damage to the crossing fibers, resulting in a bitemporal hemianopia. The pituitary tumor with suprasellar extension can compress the optic chiasm, leading to this characteristic visual field defect.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a specific type of visual field defect, making it an incorrect choice. A more specific type of visual field defect, such as bitemporal hemianopia, is expected in a pituitary tumor with suprasellar extension.
**Option B:** Homonymous hemianopia is not typically associated with compression of the optic chiasm, but rather with lesions posterior to the optic chiasm, such as those in the optic tract or beyond. This option is incorrect.
**Option C:** Quadrantanopia is a visual field defect that affects one quadrant of the visual field, either in one eye or both eyes. It is not typically associated with compression of the optic chiasm, making this option incorrect.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the type of visual field defect depends on the location of the lesion. Compression of the optic chiasm typically results in bitemporal hemianopia, while lesions posterior to the optic chiasm can result in homonymous hemianopia.
**Correct Answer:** C. Quadrantanopia