Which condition is classically associated with optic chiasm compression leading to bitemporal hemianopsia?

• A. Craniopharyngioma
• B. Pituitary adenoma
• C. Meningioma
• D. Acoustic neuroma

Answer: (B)

Bitemporal hemianopsia occurs when the optic chiasm is compressed, affecting the crossing nasal retinal fibers that carry the temporal visual fields from both eyes. The pituitary gland sits just below the chiasm, so a pituitary adenoma typically expands upward into the suprasellar space and presses on the center of the chiasm, hitting the crossing fibers first. This pattern produces loss of the outer halves of the visual field in both eyes while central vision can be preserved early on. Other nearby lesions like craniopharyngioma or tuberculum sellae meningioma can also cause chiasmal compression, but the classic association is pituitary adenoma. Acoustic neuroma does not involve the optic pathway and presents with hearing and balance symptoms instead.