Pituitary Adenoma

The base of the brain reveals a large pituitary adenoma. Note the relationship of the adenoma to the adjacent structures. The clinical finding is bitemporal hemianopsia. The hemianopsia occurs because the adenoma compresses the optic chiasm, damaging the decussating fibers. The defect is bitemporal because the nasal half of the retina forms the temporal half of the visual field of vision. The nerve fibers from the nasal half of the retina cross over to the opposite hemisphere through the optic chiasm.

A: Olfactory bulb
B: Adenoma
C: Basilar artery