CRANIAL NERVE LESIONS

Question 1

How can you tell the difference between CSF rhinorrhoea and clear mucus secretion?

Answer 1

Higher glucose concentration in CSF

Question 2

What is the most common neurological cause of anosmia?

Answer 2

Head injury that results in fracture to the cribriform plate

Question 3

Other than head injury, what other neurological causes of anosmia can you name?

Answer 3

Tumours (eg meningioma of the dura in the olfactory groove
Aneurysm of the anterior cerebral or anterior communicating artery
Raised intracranial pressure
Degenerative disorders

Question 4

What types of patients present with hyperosmia (over sensitive sense of smell)?

Answer 4

Anxious patients

Migraine patients often complain of hypersensitivity to light, smell and sound.

Question 5

What types of patients present with olfactory hallucinations?

Answer 5

Complex partial seizures of temporal lobe origin
Alcohol withdrawal
Psychotic illness
Dementia

Question 6

What is the name of the cranial nerve responsible for smell?

Answer 6

Olfactory nerve (I)

Question 7

Which part of the retina does light from the upper visual field fall on?

Answer 7

The inferior retina

Question 8

Which part of the retina does light from the lower visual field fall on?

Answer 8

The superior retina

Question 9

Which part of the retina does light from the nasal visual field fall on?

Answer 9

The temporal retina

Question 10

Which part of the retina does light from the temporal visual field fall on?

Answer 10

The nasal retina

Question 11

What are the two types of photosensitive cells in the eye?

Answer 11

Rods and cones

Question 12

Which photosensitive cells are responsible for movement in the peripheral visual fields?

Answer 12

Rods

Question 13

What are the photosensitive cells called cones responsible for?

Answer 13

Colour

Question 14

What is the macula of the retina?

Answer 14

The part of the retina specialised for perception of detailed images and colour.

Question 15

What does the physiological blind spot correspond to?

Answer 15

The optic disc, where ganglion cells converge

Question 16

Where does the optic chiasm lie in relation to the pituitary stalk?

Answer 16

Anterior to it

Question 17

Where does the optic chiasm lie in relation to the hypothalamus?

Answer 17

Inferior to it

Question 18

A lesion in the optic chiasm will mean that which part of the patient’s visual field will be affected?

Answer 18

Bilateral temporal fields

Question 19

What is the name given to the nerve that carry the optic signal post chiasm?

Answer 19

Optic tract

Question 20

Where does the optic tract end?

Answer 20

Lateral geniculate nucleus

Question 21

Where is the lateral geniculate nucleus?

Answer 21

Posterior thalamus

Question 22

What is the tectal area?

Answer 22

A few fibres leave the optic tract before the lateral geniculate nucleus and pass directly to the tectal area at the back of the upper midbrain. It mediates the light and accommodation reflexes.

Question 23

A lesion in the optic chiasm will mean that which part of the patient’s visual field will be affected?

Answer 23

Both of the temporal fields

Question 24

A lesion in the parietal part of the optic radiations will mean that which part of the patient’s visual field will be affected?

Answer 24

The lower temporal field of the contralateral eye and the lower nasal field of the ipsilateral eye.

Question 25

A lesion in the temporal part of the optic radiations will mean that which part of the patient’s visual field will be affected?

Answer 25

The upper temporal field of the contralateral eye and the upper nasal field of the ipsilateral eye.

Question 26

What are the optic radiations?

Answer 26

They are the nerve tracts carrying optic signal from the lateral geniculate nucleus to the visual cortex. Those that subserve the upper part of the visual field travel in the temporal lobe and those that subserve the lower part of the visual field travel in the parietal portion of the lateral ventricle.

Question 27

What is the calcarine?

Answer 27

This is another name for the primary visual cortex. It is found on the medial surface of the occipital lobe.

Question 28

What is the symptomatic difference between a lesion in the macular of the retina and degenerative retinopathies?

Answer 28

Macular lesions produce central or paracentral defects.

Degenerative retinopathies, such as retinitis pigmentosa, produce progressive constriction of the peripheral fields.

Question 29

When a pituitary tumour puts pressure on the optic chiasm from below which part of the visual field will be affected?

Answer 29

Bitemporal superior quandrantanopia

Question 30

When a tumour of the hypothalamus puts pressure on the optic chiasm from above which part of the visual field will be affected?

Answer 30

Bitemporal inferior quandrantanopia

Question 31

What is the blood supply to the optic chiasm?

Answer 31

Anterior choroidal artery
Internal carotid artery
Anterior communicating artery

Question 32

What is the blood supply to the optic nerve?

Answer 32

Opthalmic artery

Question 33

A unilateral lesion of the posterior cerebral artery which leads to damage of the occipital cortex causes will mean that which part of the visual field will be affected?

Answer 33

Contralateral homonymous heminopia, sparing the fibres that originate from the macula. This is because of the dual blood supply of the pole of the visual cortex which subserves macular function.

Question 34

What is papilloedema?

Answer 34

Swelling of the optic disc due to raised intracranial pressure. It is almost invariably bilateral. It causes fleeting loss of vision. On examinations acuity is normal but the blind spot is enlarged. The disc is swollen, pink and has blurred or absent disc margins.

Question 35

What is optic neuritis?

Answer 35

Inflammation of the optic nerve. Loss of central vision may be mild or severe. Eye movements, especially elevating eyes, are painful. The most common cause is demyelination either confined to the optic nerve or in multiple sclerosis.

Question 36

What are the causes of retinal or optic nerve ischaemia?

Answer 36

Embolism into the central retinal artery
Occlusion of small posterior ciliary arteries by small vessel disease or inflammation such as giant cell arteritis. Visual loss is typically painless.