Rosh Internal Medicine Boost Practice Exam

A patient presenting with headache and visual impairment due to a pituitary adenoma is likely compressing which cranial nerve?

1. Abducens nerve

2. Oculomotor nerve

3. Optic nerve

4. Trochlear nerve

The correct answer is: Optic nerve

A pituitary adenoma can lead to headaches and visual disturbances primarily due to the anatomical location of the pituitary gland, which is positioned directly below the optic chiasm. When a pituitary adenoma enlarges, it can exert pressure on adjacent structures, particularly the optic chiasm, resulting in visual impairment. The optic nerve fibers from each eye partially cross at the optic chiasm, and compression here typically causes bitemporal hemianopsia—loss of vision in the outer fields of both eyes. Visual impairment in this context is most directly linked to the optic nerve's involvement. The other cranial nerves listed may play roles in different visual or motor functions but are not primarily affected by the compression from a pituitary tumor. The abducens nerve is mainly responsible for lateral eye movement, the oculomotor nerve controls most eye movements and pupil response, and the trochlear nerve assists with the movement of the eye downward and laterally. None of these functions are as closely related to the visual impairment seen with pituitary adenomas as the optic nerve is. Therefore, understanding the pathophysiology behind the pressure effects of a pituitary tumor clarifies why the optic nerve is most significantly impacted in this scenario.