CRANIAL NERVE LESIONS Flashcards
How can you tell the difference between CSF rhinorrhoea and clear mucus secretion?
Higher glucose concentration in CSF
What is the most common neurological cause of anosmia?
Head injury that results in fracture to the cribriform plate
Other than head injury, what other neurological causes of anosmia can you name?
Tumours (eg meningioma of the dura in the olfactory groove
Aneurysm of the anterior cerebral or anterior communicating artery
Raised intracranial pressure
Degenerative disorders
What types of patients present with hyperosmia (over sensitive sense of smell)?
Anxious patients
Migraine patients often complain of hypersensitivity to light, smell and sound.
What types of patients present with olfactory hallucinations?
Complex partial seizures of temporal lobe origin
Alcohol withdrawal
Psychotic illness
Dementia
What is the name of the cranial nerve responsible for smell?
Olfactory nerve (I)
Which part of the retina does light from the upper visual field fall on?
The inferior retina
Which part of the retina does light from the lower visual field fall on?
The superior retina
Which part of the retina does light from the nasal visual field fall on?
The temporal retina
Which part of the retina does light from the temporal visual field fall on?
The nasal retina
What are the two types of photosensitive cells in the eye?
Rods and cones
Which photosensitive cells are responsible for movement in the peripheral visual fields?
Rods
What are the photosensitive cells called cones responsible for?
Colour
What is the macula of the retina?
The part of the retina specialised for perception of detailed images and colour.
What does the physiological blind spot correspond to?
The optic disc, where ganglion cells converge
Where does the optic chiasm lie in relation to the pituitary stalk?
Anterior to it
Where does the optic chiasm lie in relation to the hypothalamus?
Inferior to it
A lesion in the optic chiasm will mean that which part of the patient’s visual field will be affected?
Bilateral temporal fields
What is the name given to the nerve that carry the optic signal post chiasm?
Optic tract
Where does the optic tract end?
Lateral geniculate nucleus
Where is the lateral geniculate nucleus?
Posterior thalamus
What is the tectal area?
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.
A lesion in the optic chiasm will mean that which part of the patient’s visual field will be affected?
Both of the temporal fields
A lesion in the parietal part of the optic radiations will mean that which part of the patient’s visual field will be affected?
The lower temporal field of the contralateral eye and the lower nasal field of the ipsilateral eye.
A lesion in the temporal part of the optic radiations will mean that which part of the patient’s visual field will be affected?
The upper temporal field of the contralateral eye and the upper nasal field of the ipsilateral eye.
What are the optic radiations?
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.
What is the calcarine?
This is another name for the primary visual cortex. It is found on the medial surface of the occipital lobe.
What is the symptomatic difference between a lesion in the macular of the retina and degenerative retinopathies?
Macular lesions produce central or paracentral defects.
Degenerative retinopathies, such as retinitis pigmentosa, produce progressive constriction of the peripheral fields.
When a pituitary tumour puts pressure on the optic chiasm from below which part of the visual field will be affected?
Bitemporal superior quandrantanopia
When a tumour of the hypothalamus puts pressure on the optic chiasm from above which part of the visual field will be affected?
Bitemporal inferior quandrantanopia
What is the blood supply to the optic chiasm?
Anterior choroidal artery
Internal carotid artery
Anterior communicating artery
What is the blood supply to the optic nerve?
Opthalmic artery
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?
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.
What is papilloedema?
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.
What is optic neuritis?
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.
What are the causes of retinal or optic nerve ischaemia?
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.
