A 34-year-old woman visits her physician with a complaint of severe headache for two months. She took several kinds of analgesics with no significant improvement. Her headache is worse in the morning and improved by doing day activities. Imaging studies and laboratory tests confirm the diagnosis of pituitary adenoma.
Which of the following is the most likely effect of this tumor on vision?
A- Homonymous hemianopsia
B- Binasal hemianopsia
C- Bitemporal hemianopsia
D- Superior hemianopsia
Answer and Explanation
The pituitary gland is located just below the optic chiasm, where the nasal (medial) retinal fibers from both eyes cross. A pituitary adenoma can compress the optic chiasm, leading to loss of vision in the temporal (lateral) visual fields of both eyes, a condition known as bitemporal hemianopsia.
Homonymous hemianopsia occurs with lesions posterior to the optic chiasm (e.g., stroke or tumors affecting the optic tract, lateral geniculate body, or occipital lobe). It causes visual loss in the same side of both eyes (e.g., right homonymous hemianopsia = loss of right visual field in both eyes).
Binasal hemianopsia is rare and usually caused by bilateral lateral compression of the optic chiasm (e.g., from calcified carotid arteries). A pituitary adenoma does not typically cause this pattern.
Superior hemianopsia occurs in specific optic radiation lesions, such as temporal lobe lesions affecting Meyer’s loop, leading to a superior quadrantanopia (“pie in the sky” defect). Pituitary adenomas do not cause this type of visual loss.
The correct answer is C
More Repeated USMLE Questions Step 1
Check this Review Book for Step 1