Wed17November0747PM 4

A 53-year-old woman with a pituitary macroadenoma presents for transsphenoidal surgery.

Which one of the following options is the visual field defect most often caused by such lesions?

(Please select 1 option)

Central scotoma

Monocular visual loss

Homonymous hemianopia

Cortical blindness

Bitemporal hemianopia Correct

Explanation

Compression of the optic chiasma by pituitary tumours predominantly affects the neurones that decussate at this site. These neurones emerge from the nasal half of the retina and convey the temporal half of the visual field, so bitemporal hemianopia is classically found.

The optic nerve is formed by the axons of ganglion cells in the retina.

It leaves the orbit via the optic foramen and projects to the lateral geniculate body in the thalamus. En route, the nasal fibres decussate forming the optic chiasma above the sella turcica. From the lateral geniculate body, the optic radiation projects to the occipital cortex.

Lesions at different sites in this pathway will produce characteristic visual field defects:

Scotoma reflect partial retinal or optic nerve damage

Complete optic nerve injury produces monocular visual loss

Bitemporal hemianopia is seen with pathology at the optic chiasma

Homonymous hemianopia with lesions compromising the optic radiation and

Cortical blindness with occipital cortex pathology.

Answer Statistics

1

1%

2

6%

3

94%

Times answered: 247