Third cranial nerve palsy

Question 1

What are the causes of a medical third cranial nerve palsy?

Answer 1

diabetes
atherosclerosis
hypertension
vasculitis

Question 2

what are the causes of a surgical third cranial nerve palsy?

Answer 2

posterior communicating artery aneurysms

cavernous sinus lesions i.e. infection, tumour, thrombosis

Question 3

what is difference in the presentation between a medical and surgical third cranial nerve palsy?

Answer 3

medical:
- miosis
- down and out gaze

surgical:

• pupillary dilatation
• down and out gaze

Question 4

what is the difference in the pathophysiology of surgical and medical third cranial nerve palsy?

Answer 4

medical

• damage to the nerve occurs from the blood supply and therefore affects inner fibres
• parasympathetic fibres responsible for constriction run on the outside so aren’t affected

surgical
- external compression affects fibres on the outside too therefore affecting the parasympathetic fibres = pupillary dilatation

Question 5

what muscles does the third cranial nerve supply?

Answer 5

superior levator palpebras (elevated eyelid)
constrictor papillae
extra-ocular eye muscles except lateral rectus (CN VI) and superior oblique (CN IV)