Questions
1. A 63 year old male patient presents with a complete right ptosis and when you raise the eyelid you can see that his eye looks down and out. What cranial nerve palsy would be suspected
An Oculomotor Nerve palsy (IIIrd)
- Dilated pupil
- Complete ptosis
- Eye is down and out
2. What is the difference between a surgical (compression) form of the above cranial nerve palsy
Surgical (compression) cause of IIIrd neve palsy is usally complete with
- Dilated pupil
- Complete ptosis
- Eye is down and out
Non surgical IIIrd neve lesions often have a normal pupil
- Normal pupil
- Complete ptosis
- Eye is down and out
3 Why is the pupil normal with a medical IIIrd nerve palsy
4. A patient came in after a head injury whilst skiing. The patient is initially GCS 15 but in the past 1 hr the patient now has a GCS of 6 and the right pupil is fixed and dilated. Can you explain
I suspect there may be an extradural haematoma with compression of the brain and herniation of the right temporal uncus which is compressing the right Oculomotor nerve. It is an ominous signs. Urgent CT head and neurosurgical intervention is needed.
5. A patient presents with a complete IIIrd nerve palsy which has worsened over 2 days and now a sudden thunderclap headache. CT shows a SAH. What can you say about the cause ?
This sounds like an enlarging berry (saccular) aneurysm on the posterior communicating artery which is very close to the IIIrd nerve. The aneurysm gradually grows and compresses the nerve. It may also be seen with a a superior cerebellar artery aneurysm but this is much less common. This is a neurosurgical emergency and needs urgent CT and ITU / neurosurgical referal
6. Can you list the functions of the IIIrd Cranial nerve
- Motor (moves the eye) to superior, inferior and medial rectus, and the inferior oblique (all except lateral rectus and superior oblique).
- Parasympathetic (constricts the pupil) innervation to the eye.
- Eyelid: It also lifts the eyelid as it innervates levator palpabrae superioris.
7. You see a patient who presents with a sudden right IIIrd nerve palsy and weakness down the right arm and leg. The CT looks normal
This sounds like Weber's syndrome which is an infarct in the midrain around the cerebral peduncle.
8. Which eye muscles does the Oculomotor nerve supply and what is their effect
- Medial Rectus: YES : pulls eye medially
- Lateral rectus: NO this is abducent VIth nerve
- Superior rectus: YES: pulls eye down
- Inferior rectus: YES: pulls eye up
- Inferior oblique: YES: Pulls eye down
- Superior oblique: NO this is trochlear IVth nerve : Pulls eye up and out
9. Where is the 3rd and 4th Nerve Nucleus
They ae both found in the dorsal midbrain near the midline
10. Question
- Formed in the Midbrain and passes out through anteriorly between cerebral peduncles
- Passes anteriorly, below closs to the posterior ocmmunicating artery and the superior cerebellar artery
- The nerve pierces the dura mater and enters the lateral aspect of the cavernous sinus.
- The nerve leaves the cranial cavity via the superior orbital fissure.
- Then it divides into superior and inferior branches.
- Superior branch: supplies SR and LPS. Sympathetic fibres run with the superior branch to innervate the superior tarsal muscle.
- Inferior branch: supppies inferior rectus, medial rectus and inferior oblique.
- Parasympathetic fibres to the ciliary ganglion, which ultimately innervates the sphincter pupillae and ciliary muscles.
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